Experience gained from the space nuclear rocket program (rover)
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LA-10062-H
History
- .
.
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1.
.
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Experience Gained from the
Space Nuclear Rocket Program (Rorer)
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For Reference
Not to be taken from this room
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Los Alamos National L:at>oratory
LosAlamos,Newtv1ex1CO 87545
An Affirmative'Action/Equal Opportunity Employer
This work was supported by the Air Force Weapons Laboratory, Kirtland Air Force
Base, Kirtland, New Mexico.
�-
DISCLAIMER
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LA-10062-H
History
UC-33
Issued: May 1986
Experience Gained from the
Space Nuclear Rocket Program (Rover)
Daniel R. Koenig
L
r.
n 'Q' � f& n0lf"n'hlt(5\ � LosAlamos National Laboratory
��� �Li@U Li Li�� LosAlamos,NewMexico87545
CONTENTS
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
I.
OVERV I EW
1
II.
H I STORICAL PERSPECT I VES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
REACTOR DEVE LOPME NT.
7
III.
IV.
Ki w i - A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
B.
Ki wi-B and NRX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
C.
Phoeb u s
D.
Pewee
E.
Hucl ear Furnace , NF - 1 . ••••••••••••••••••••••. •••••••••••••••••••• 1 2
F.
Fuel Devel opment
• • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • . • •
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• • • . • • • • • • • • • • • • • • • . • • . • • • • • . • • • • • • • • • • • • • • • • • • • • • •
A.
E ng i ne Tests
B.
E ngi ne Des i gn Improvements .
C.
NERVA a nd Smal l E ng i ne De s i gn s
D.
Component Devel opment
E.
Testi ng Fa c i l i ti es
•
• • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
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• • • . • • . • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
A.
F l i ght Engi ne
B.
Space Power Generati o n
C.
Dual -Mode Reactors
SUMMARY.
• • • • • •
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
FUTURE D EVE LOPMENTS
•
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
A.
ENGI NE D EVE LOPMENT
V.
VI
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10
11
13
16
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17
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21
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VI I .
ACK NOWL E DGME NTS
VII I .
SUPPLEMENTAL B I BL IOGRAPH Y ••••••••••••••••••••••••••. ••••••••••••••••• 24
REFERENC ES
TAB LES
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • •
• . . . • • . . • . . • . .
FI GURES
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
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. . • . • •
24
26
30
32
v
E XPERIENCE GAINED FROM THE SPACE NUCLEAR ROCK ET PROGRAM ( ROVER )
by
Dan i e l R . Koe n i g
AB STRACT
In 1955 the U n i ted States i ni ti ated Proj ect Rover to deve l o p a nucl ear rocke t
e ngi ne for use i n defense systems and space expl oration.
As part of that proj ect,
Lo s Al amos devel oped a seri e s of reactor des i gns and hi gh-temperature fuel s . Three
h i gh-power reactor seri es c u l mi nated in P hoebu s , the most powerful reactor ever bui l t ,
wi th a peak power l evel o f 4080 MW . Two l ow-power reac tors served as tes t beds for
e val uation of hi gh- temperature fuel s and other components for ful l - s i ze nucl ear rocket
reactor s . Lo s Al amo s devel oped a nd tested several fuel s , i ncl udi ng a fuel con s i sti ng
o f highly enriched uc2 particles, coated wi th pyrolyti c graph i te , and i mbedded in a
graph i te ma tri x and a compos i te fuel that formed a conti nuous web of uran i um zi rconi um
carbi de th roughou t the graphi te matri x . The program produced the desi gn of the Smal l
Engi ne , wi th a possi bl e l i fetime of several hours i n space .
The Astronucl ear Laboratory of the Westi nghouse E l ectr i c Corporati o n , havi ng re
spons i b i l i ty for devel op i ng a pro totype reactor based on the L o s Al amos des i gn, con
ducted an extens i ve and succe s sful test seri e s that c u l mi nated wi th the NRX-6 reactor
test that ran conti nuously for 60 mi nutes at des i gn power.
Aeroj et-General Corporati on ,
prime contractor for devel opment of a compl ete
rocket engine , developed two engi ne test seri e s , the NRX/EST and the XE ' , to eval uate
startu p , fu l l -power, and shutdown cond i ti o n s i n a vari ety of a l t i tude and space simu
l ati o n s .
The Un i ted States termi nated Proj ect Rover i n J a nuary 1 9 7 3 a t the poi nt of fl i ght
engi ne devel opment, but testi ng had i ndi cated no technol og i cal barriers to a succes s
ful fl i ght system. Conceptual stud i e s al so i ndicated that nucl ear rocket eng i ne tech
nol ogy coul d be appl i ed to the generati on of el ectri c power i n spac e .
I.
OVERVIEW
fi nal ma s s
In 1 955 the Un i ted States embarked on a pro
gram to devel op a
nucl ear rocket eng i n e .
The
program , k nown as Proj ect Rover, wa s i ni ti ated a t
Lo s
Al amos
Nati onal
Laboratory ,
then
cal l ed
Lo s Al amos Sc i enti f i c Laborato ry .
The concept to
be
hy drogen-c ool ed
pursued
was
a
sol i d-c ore ,
at
earth-e scape veloc i ty , a s exempli
fied i n Fi g . 1 .
In J anuary 197 3 , after a total
e xpendi ture of approximately one and a hal f bi l
l ion
dol l ar s ,
tec h n i cal
the
succe s s )
program
wa s
eng i ne s changed several
of the pro gram .
space .
The
because
a
of
The expec ted appl i cati on for nucl ear rocket
a
in
termi nated
j udged
changi ng national pri ori ti e s .
reactor i n which the ex i ti ng gas expanded through
rocket nozzl e and d i sch a rged
( al though
times duri ng the course
At f i r s t , nucl ear rockets were
moti vati o n for the devel opment of such a rocket
consi dered a potenti al back-up for i nterconti nen
engi ne was that it coul d pro v i de about twice the
l)
spec i fic
impul se (
of
the
best
chemical
tal
rockets and , corre spondi ngly ,
fl i ght .
factor of 5 i n
a reducti on
by
a
the rati o of ta ke-off ma s s to
bal l i sti c m i s si l e ( ICBM)
propul s i o n .
Later
they were menti oned a s a second stage for l u nar
A more durabl e possi bi l i ty wa s the i r use
in manned Ma rs fli ght s .
After pl a n s for manned
Mar s fl i ghts were abandoned as too amb i ti ou s , the
La boratory of the Westi nghouse E l ectri c Corpora
fi nal
t i on
pos s i bi l i ty advocated for nuc l ear e ng i ne s
wa s ea rth orb i t-to-orbi t tran sfer.
( WA NL ) ,
the
pri nc i pal
s ubcontractor
to
devel op the NERVA nucl ear reac tor.
When anal y s i s showed chemical rockets to be
A seri e s of reactors and engi nes was tes ted
more economical for orbi t-to-orb i t mi s s i o n s , the
at the Nucl ear Rocket Devel opment Stati on ( NRDS )
need for a nuc l ear engi n e for rocket vehi c l e ap
i n the test si te at J ackas s Fl ats i n Nevada where
p l i cation ( NERVA ) evaporate d , and the program was
maj or testi ng fac i l i ti es were bui l t for the Rover
cancel ed before achi evement of a fl i ght demo n
program ( Fi g . 4 ) .
s trati on.
The des i gn and the objecti ves of the
NERVA are shown i n Fi g .
2.
Most o f the des i gn
objecti ves were met or exceeded duri ng the course
NERVA
s l i ghtly
D u ri ng
d i sas sembly faci l i ty and two testi ng faci l i ti e s
for the resea rch a n d engi ne reacto r s .
in
Fi g .
pressurized,
operation,
2
is
attached
l i qu i d
the
hydrogen
hydrogen
engi n e by a turbopump .
to
is
fed
a
tan k .
to
the
The hi gh-pressure fl ui d
fi rst regenerati vel y cool s
the
nozzl e
and
the
The tes t
nuc 1 ear rocket reactors i s
; ng program for the
summari zed i n Fi g .
o f the pro gram .
The
These i ncl uded an a ssemb l y and
5.
It was i ni ti ated wi th a
fami ly of research reactors named K i wi
fl i ghtl e s s
b i rd of New Zeal and) .
( for the
The
program
obj ecti ves were fi rst to demon s trate the proof of
pri nc i p l e ,
then to establ i sh
technol ogy
and
devel op
the bas i c
sound
desi gn
reactor
c oncept s .
reactor refl ector as shown i n Fi g . 3, then passes
These reactors were the fi rst t o demon s trate the
through the reactor core .
u se of h i gh- temperature fuel s and to operate wi th
No t shown in Fi g . 3 i s
a paral l el cool ant c i rc u i t to cool the c o re - s u p
l i qu i d hydroge n .
p ort
is
nated wi th the K i wi -B4E reactor, which operated
heated suffi ci entl y to dri ve the turbopump befo re
for 1 1 . 3 mi n at a cool ant exi t temperature above
the cool ant rej o i n s the ma i n fl ow at the reactor
1 890 K and for 95 s at 2005 K and a power l evel
t i e rods ;
i nl et .
in
the
c i rc u i t the
The core conta i ns
sol id
together
by
cool ant
hexagonal
1 ateral
fuel
e l ements
banded
support
spri n g s .
Long i tudinal hol e s i n the fuel el ements
provi de cool ant channel s for the hy drogen propel
of
940 MW .
The K i wi testi ng seri e s cul m i
These
tests
l ed
to
the
Nuc l ea r
Reactor Experi ment ( NRX) seri e s o f devel opmental
reacto r s .
The i r goal was to demons trate a spe
c i f i c i mpul se of 760 s ( 7450 m/ s ) for 60 mi n at a
l an t , whi ch i s heated to 2400-2 700 K and fi nal l y
thrust l evel of 245 kN ( 5 5 000 l b ) i n a 1 100-MW
expanded through a thru st nozzl e .
reactor.
in
the
Rotati ng drums
These objecti ves were exceeded i n the
refl ector
contai n i ng
neutron
absorber
l ast tes t of
provi de
reacti v i ty
control
of
the
whi ch operated f o r 62 m i n at 1 100 MW a n d a tem
neutron energy
perature o f 2200 K , wi th only an $0 . 1 1 reacti v i ty
materi al
reacto r, wh i ch has an epi therma l
spectrum.
The
aim
des i gn i ng
of
the
Rover
a nd demonstrati ng
program ,
a
rocket
seri e s ,
the
NRX-6
reactor ,
1 oss.
A nother s e r i e s of research reacto r s , cal l ed
be s i d e s
practi cal
that
P h oebu s ,
was
devel oped wi th
obj ecti ves
i mpul se to 825 s ,
to
i n
engi ne , wa s to achi eve the hi ghest-po s s i bl e pro
crea se the spec i f i c
i ncrea s e
p el l ant temperature ( s p ec i fic i mpul se i s propor
t h e power den s i ty by 50%, a n d i ncrease t h e power
tional to the square root of the temperatu re) for
l evel to the range of 4000-5000 MW .
the
b i l i ti e s were demo nstrated i n the P hoebus-lB and
durati o n
hour s ) .
of
Thi s goal
potenti a 1
mi s s i on s
( severa 1
i mp l i ed a s trong technol ogy
Phoebu s-2A reactor s .
These capa
The l atter , the most power
ful reactor ever bui l t , ran for 12 m i n at 4000 MW
devel opment program i n reactor fuel s .
Lo s Al amos Nati onal Laboratory was gi ven the
and reached a peak power of 4080 MW .
The 1 as t
rol e of e stabl i shi ng a b a s i c reactor des i g n and
two fami l i e s of re searc h reactors , Pewee a nd the
o f l eadi ng the fuel s devel opment effort .
Nucl ea r Furnace ( NF ) , were tested only once each .
Other
k ey p l ayers were the Aerojet-General Corp orati on,
They
the
comp l ete
respecti vel y , des i gned primari l y a s test beds to
Astronucl ear
d emonstrate the capabi l i ti e s of hi gher- temperature
prime
rocket
2
contractor
eng i ne
to
system,
devel op
and
the
the
were
l ower-power reactors,
500
and
44 MW
fuel el ements .
and
NF-1
Pewe e-1 ran for 40 mi n at 2555 K ,
operated
for
109 mi n
at
an
average
For
compari son,
reactors
is
the
pl otted
mass
versus
of
several
power
in
Rover
l evel
in
F i g . 10 .
cool ant exi t temperature of 24 50 K .
I t was al s o recogn i zed that the design of a
A n eng i ne devel opment test program was p a rt
I ts objecti ves
nucl ear rocket eng i ne coul d be al tered so as to
were to tes t nonnucl ear system component s , deter
provi de conti nuous statio n-keep i ng power for the
m i ne system characteri s t i c s duri ng startup , ful l
mi s s i o n s .
power , and shutdown condi ti on s , eval uate control
rocket systems were i ni ti ated i n
concept s , and qual i fy the engi ne test- s tand oper
one
of the technol ogy demon s trati o n .
ati o n s
in
a
downwa rd- f i ri ng
confi gurat i o n wi th
s i mul ated al ti tu de and space cond i ti on s .
These
D e s i gn
mode
was
second ,
a
(4•5l
stud i e s
the
normal
c l osed-l oop ,
for
s uch
dual -mode
1 9 7 1 -72 where
propul s i on
l ow-power
and
the
el ectrical
mod e .
The Rover program was termi nated i n J a nuary
obj ecti ve s were met o r exceeded in the Nucl ear
Reactor Experi ment/Engi ne System Test
(N RX/EST )
1973 at the poi nt of fl i ght engi ne devel opment .
a nd Ex peri mental Eng i ne ( XE ) programs.
A proto
For a fl i ght sys tem ,
i t woul d be
necessary
to
type fl i ght e ngi n e system, X E , consi sti ng o f a
veri fy the fl i ght reactor and e ng i ne des i gn and
f l i ght- type reactor wi th nonnucl ear fl i ght compo
to perform l i fe and reproduc i bi l i ty testi ng .
nen t s , was tested i n a space-si mul ated envi ro n
there a re no apparent barri ers to a succes sful
ment , performi ng some 28 s tarts a n d re start s .
n ucl ear rocket.
A chronol ogy o f the maj o r tests conducted
duri ng the Ro ver program i s s h own i n F i g . 6 .
The
technol ogy
But
devel oped duri ng the Rover
program i s d i rectly appl i cabl e to the generati on
The maj o r emph as i s of the reactor devel op
of el ectri cal
power i n
space ,
e spec i al l y
l a rge
ment program was to i ncrease the reactor cool ant
( m ul timegawatt) bursts of el ectr i c a l power.
exi t temperature because the spec i f i c impul se i s
an open-l oop converter system , one wou l d s i mpl y
proport i onal to the square root o f that tempera
repl ace the rocket nozzl e wi th a power conver s i on
ture and to i ncrea se the operati ng time of the
sy stem .
reactor.
wou l d be i nvo 1 ved because
The success of th i s part of the program
i s i l l us trated i n F i g . 7 .
Cool ant exi t tempera
Some
redes i gn
of
the
core
For
parameters
the power converter,
unl e s s it were a magnetohydrodynami c ( MHD )
sy s
tures above 2 50 0 K and operati ng time over 2 h
tem , coul d not operate at the h i gh temperature of
were demon s trated .
the Rover reacto r s .
The cumul ati ve time-a t-power
The s ta rtup time for such a
for the e nti re Rover program i s shown i n Fi g . 8 .
power pl ant woul d
be
The maj o r performance s ach i eved du ri ng the pro
al l owabl e
reactor
gram are s ummari zed i n F i g . 9 .
about 83 K/s .
The Rover program was termi nated befo re a l 1
rate
of
l i mi ted
in
part
temperature
by
the
change ,
However, a more severe 1 i m i tati on
i s in the propel l ant feed system , w h i ch requ i re s
60
s
of the NERVA objecti ves coul d be demonstrated , i n
approxi mately
parti cul a r , before showi ng that a n e ngi ne coul d
before chi 1 1 - down and to chi l l vari o u s pa rts of
be operated for
10
h
wi th
up
to 60
s tart i ng
cyc l e s wi th a rel i abi l i ty of 0 . 99 5 .
bei ng pl aced on smal l e r engi nes for the orbi ta l
A comprehensi ve de s i gn study
wa s don e on a 367-MW , 7 2 - kN
the
so-cal l ed
Smal l
( 1 6 000-1 b) e ngi ne ,
( 2 •3)
The total
Engi n e .
mas s o f thi s e ng i ne was 2550 kg , and i ts overal l
l ength was 3 . 1
fol ded
pos i ti o n .
m wi th
the
nozzl e
The engi ne ,
In
addi tion,
pump cavi tati on
there woul d b e time
1 i mi tati o n s i mp osed by the power conve r s i o n sy s
Toward the end o f the program, emphasi s was
transfer mi s s i on.
the e ng i ne .
t o overcome
ski rt
together
tem.
A cl osed- 1 oop sys tem woul d re qui re further
rede s i gn to i ncorp o rate the gas c i rc u l ators, and
the core des i gn woul d have to be adj usted for the
h i gher i nl et temperatures .
A s concerns dual
el ectri cal - power modes ( a
in
a
c onti nuo u s ,
wi th
a
hi gh-power mode ) much of the technol ogy and many
l ow-power
mode
and
a
short-tenn,
hy drogen tank c ontai n i ng nearly 13 000 kg of pro
s tud i es
pel l an t , coul d be carri ed on the space shuttl e .
appl i c abl e i f th e h i gh-power converter i s to be a
devel oped
under the Rover
program
a re
gas system .
3
I I.
H I STORICAL PERSPECT I VES
�-
Thi s chapter summari zes the maj o r events i n
the h i story o f the Rover
program.
for the tes t s ummari e s wa s
I nformati on
obtai ned
primari l y
1 945-1954
U SAF
Sci enti f i c
Adv i s o ry
Boa rd
s tudied the u se o f n ucl ear propul s i on for rocket
systems .
The fi rst reactor test, K i wi - A , i s
s uccessfu l l y
at
the
Nevada
Test
The reactor operated for 5 min
i nformati o n .
In 194 5 , at the suggesti o n of Theodore von
the
conducted
(7 , 8 )
S't
i e.
at
70 MW and provi ded i mportant design and materi al s
from Ref s . 6-8 .
Karma n ,
1 959
However, because o f a l ack of a c l ea r
The fuel was hot enough ( 2683 K ) to
mel t carbi de fuel
e l ements.
The
uo 2
l oaded , p l ate-type fuel e l ements and was cool ed
w i th
abl e materi al s , and the techni cal di ffi cul t i e s o f
tai ned a central
devel o p i n g s uch a
amount
was recommende d .
no acti o n
Neverthel e s s , paper stud i e s o f
nucl ear rocket systems were pe rformed duri ng th i s
( 9 , 10 l
ga seou s
of
hy drogen .
The
u ncoated ,
reactor
core
con
i sl and of
D o to reduce
2
material
req u i red
fi s s i onabl e
cri tical i ty .
Control
the
for
rods were l ocated i n th i s
i sl and .
period .
1 960
�-
1954
Von Karman aga i n suggests tha t , i n v i ew o f
Vi brati ons i n the
damage i n the graph i te
reactor empl oyed
need for s uch systems , the shortage o f fi s s i on
propul s i on system ,
part i c l e s .
core produced s tructural
Ki wi - A ' i s tested for nearly 6 m i n
a t 8 5 M W to demonstrate a n i mproved fuel -el ement
the need f o r I CBMs and t h e good s upp l y o f fi s
desi g n .
s i onabl e materi al , the S c i enti fic Adv i sory Board
uo - l oaded fuel e l ements c ontai ned i n graph i te
2
modul e s . The fuel el ement had four ax i al cool ant
recons i de r nucl ear propul s i o n .
1 955
October 1 8 .
In a fi nal
report , an ad hoc
mends that because of the potenti al l y h i gh spe
i mpulses
wi th i n
the
rea l m
of
i mmedi ate
achi evement from the nuclear rocket , substanti a l
devel opment work s houl d b e started on t h e nucl ear
No vember 2 .
is
L o s Al amos
The n ucl ear rocket propul s i o n
established
and
Laboratori e s .
u sed
as
Lawrence
Projec t
L i vermore
Several conceptual
desi g n s al ready had been
at
Rover
Sci enti f i c
nucl ear rocke t
under study . (ll)
s h o rt ,
by a
cyl i n dri cal ,
chemi cal
vapor
depo s i t i on ( C VD ) proces s .
August 2 9 .
A Memorandum o f U nderstand i ng
defi ni ng NASA and AEC respon s i bi l i ti e s and e s tab1
i shi ng a j o i nt nucl ear program offi ce , the S pace
Nucl ear Propul s i o n O ffice, is s i gned .
Oc tober 1 0 .
Kiwi - A3 reactor i s operated i n
exc e s s o f 5 m i n at 100 MW .
rocket system.
program
reactor
c h annel s coated w i th NbC
c onvni ttee of the Sci enti f i c Adv i sory Board recom
c i fi c
The
The fuel wa s s i mi l a r
to that u sed i n the pre v i ous tes t .
earli e r
tests,
As wi th the
c o re structural damage occurred ,
i ndicati ng
that
tensi l e
s tructures
shoul d
be
l oads
avoi ded .
on
graph i te
Th i s
experi ment
But
was the th i rd and l ast i n the K i wi - A seri e s of
the concep t chosen to be pursued was a sol i d
proo f-of-pri nc i p l e tests conducted by Los Al amo s .
core , hydrogen- c ool ed reactor that woul d expand
The test seri e s demonstrated that thi s type o f
hi gh-power-dens i ty
gas through a rocket nozzl e .
March
18.
The
Atom i c
Energy
gram as a resul t o f budget restri c ti o n s and
a
Department of Defense reconvnendati on for a more
of
support .
cou l d
be
control l ed
1961
Commi s s i o n
( AEC) dec i de s t o phase Li vermore o u t o f the pro
moderate l evel
reactor
and coul d heat hy drogen gas to high temperatures .
1957
The l atter stenvned
J u ne-J u l y .
General
for
I n du s tri al contractors , Aerojet
the rocket engi ne and Westi nghouse
E l ec tri c Corp orati o n
l ected to p e rform
for the reactor,
the
nucl ear
rocket
are
se
devel o p
from the earl i e r- th an-a nti c i pated avai l abi l i ty of
ment phase.
chemical
program wa s i niti ate d at the Lockheed Corporati o n .
I CB M s ,
wh i ch
reduced the
devel opment o f n ucl ear propul s i o n .
4
u rgency
for
The reactor i n- f l i ght tests ( RI FT )
December 7 .
new
seri e s ,
reactors
were
refl ector
nozzl e .
Kiwi - B lA reactor ,
is
tested
by
desi gned
control
and
Los
for
a
fi rst o f a
Al amo s .
1 100 MW
K iw i -B
and
regenerati vel y
used
cool ed
Thi s test was the l ast to be run wi th
gaseous hydrogen cool ant.
After 30 s of opera
and fi nd sol utions for the severe s tructural dam
age that was
tests .
no power.
The p l anned maxi mum power of 300 MW was
a s l i mi ted by the capabi l i ty of
the
nozzl e wi th ga seous hy drogen cool ant.
The
core
consi sted
of
l oaded fuel
el ement s ,
seven
cool ant channel s
axial
tube- c l addi ng
The
cyl i ndri cal
NbC
fuel
coated
uo 2
havi ng
by
These tests were performed wi th gas
n i trogen ,
were compl etel y
f i rst to operate wi th l i qui d hydrogen.
�·
The test
n ated
Fol l ow i ng
a
smooth ,
stabl e
start , the run was termi nated after a few seconds
were ejected from the reactor.
The core empl oyed
Thi s was al so t h e fi r s t time
K i wi-B4A ,
prototype
tubes
s
The tes t was term i
a t ful l
ruptured .
power when
The core
several
consi sted
of
c l add i ng process .
August 2 8 .
K i wi
reactor,
K i wi -B4E , the e i ghth and fi nal
is
tested
by
Los
Al amos .
The
reactor wa s operated for more than 12 mi n ,
the same type of fuel as Kiw i -BlA.
teste d .
the fi rst test at ful l
uo -l oade d ,
1 9-hol e ,
hexagonal
2
fuel el ements wi th bores NbC coated by the tube
at 900 MW when p o rti ons of several fuel el ements
30 .
Based o n resul t s
i s c arri ed out wi th no i nd i cati o n
after 60
ful l - l ength,
a
they
i n el imi nati ng core
a nuc l ear rocket reacto r .
abi l i ty o f the sy stem to s tart up and run u s i ng
as
s uccessful
K i wi -B4D ,
desi gn power,
nozzl e
November
and
vi brations were made.
met i ts primary objecti ve o f demonstrati ng the
i ntended
hydroge n ,
a comp l etel y automati c start was accompl rshed for
Kiwi - B lB reactor tes t i s the
hy droge n .
and
due to fl ow- i nduced v i brati on s .
of core vi brati o n .
1 962
l i qu i d
hel i um ,
demonstrated that the structural core damage was
a
el ements were
conta i ne d i n graph i te modul e s .
September l .
to
o f these tes ts a n d analyses, d e s i g n c h anges that
about 66 cm l ong ,
proces s .
reactor
referred
t i cal to the power reactors except that they had
eous
run.
desi gnati on
no fi s s i onabl e materi al a n d , therefore , produced
sure vessel
ach i eved ,
col d-fl ow
reactor te sts that contai ned fuel e l ements i den
t i o n , a hydrogen l eak i n the nozzl e a nd the pre s
i nterface forced termi nati o n of the
observed i n the previ ous
The
the
fl i ght
fi r st
desi gn
reactor,
is
The power run was termi nated at about
w h i ch
at
nearly
ful l
power.
reactor operati on wa s
8 mi n
were
smooth
a nd
s tabl e .
duration
by
wa s
l i mi ted
the
avai l ab l e
of
The
Its
l i qu i d
the 50% l evel when bri ght fl a shes in the exhaust
hydrogen storage capac i ty .
O n September 10 , the
( c au sed by ejection of core materi al )
reactor was
ran
wi th i ncreasi ng frequency .
occurred
Subsequentl y , i nten
s i ve analyses and component testi ng
were
con
power for 2 . 5 mi n .
age .
The core consi sted for the fi rst time of
el ements,
channel s
extruded ,
l oaded
sti l l
1 9-hol e ,
hexagonal
wi th
were NbC coated
uo •
2
by the
The
fue l
cool ant
at
nearly
Thi s was the f i r s t demon stra
hexagonal
fuel
el ements,
time wi th
uc
p a rti c l e s .
l oaded for
The
the
bore s
2
coated by the tube- c l addi ng process.
September.
December.
The
RIFT
positi oned
program
is
cancel l ed .
there
is
fi rst
were
N bC
Measurements , at zero power, of
the neutroni c i nterac ti on of two Kiwi
1 963
ful l
The core consi sted of ful l -l ength , 1 9-hol e ,
tube-cl addi ng
proce s s .
and
t i o n of the reactor' s abi l i ty to re start .
ducted to determi ne the cause of the core dam
ful l -l ength ,
re s tarted
reactors
adj acent to each other veri fy
l i ttl e
i nteraction
and
tha t ,
that
from
a
I t was deci ded to rev i se the nucl ear rocket pro
n ucl ear standpoi n t , nuc l ear rocket eng i ne s may be
gram to p l ace empha s i s
operated i n c l u sters s i mi l a r to chemi cal e ngi ne s .
on
the
devel opment
of
ground- b ased sys tems and defer the devel opment o f
fl i ght systems .
reactor
col d-fl ow
tests
NRX-A2
i s the
fi rst
NERVA
tested at ful l power by Westi nghou s e
7)
T h e reactor operated i n the range
E l ec tri c . (
1 963-1 964
Several
September 24.
of
Kiw i - B-type
reactors a re carried o ut to determi ne the cause
of hal f to ful l power ( 1 100 MW) for about 5 m i n ,
a
time
l i mi ted
by
the
avai l abl e
hydrogen
gas
5
supp l y .
The tes t was succes sful and demons trated
an equi val ent vacuum speci f i c i mpul se of 760 s.
The
reactor
wa s
successful l y
restarted
on
October 15 to i nvesti gate the margin of control
i n the l ow-fl ow, l ow-power regime .
January
12.
agai n
at
ful l
power
(-1100 MW )
J u ne 2 3 for 1 4 . 5 mi n to bri ng the total operati ng
time at ful l power to hal f an hour.
The l i qu i d
hydrogen capac i ty of the test faci l i ty w a s not
tion at de s i g n power .
Kiwi -TNT
( Tran s i ent
Nuc l ea r
1 967
i s succes sfu l l y compl eted by L o s Al amo s .
I n th i s fl i gh t safety tes t , a K i wi -B- type reactor
wa s del i beratel y destroyed by pl aci ng
it o n
a
23.
February
Phoebus-lB
is
operated
were
at desi gn power of 1 500 MW .
The
prima ry
p u rp ose of
of
h i gher-power operati on affected the reacto r .
the reactor behav i or du ri ng a power excu r
( 12, 13)
sion.
23.
N RX-A3 reactor i s operated for
a bout 8 m i n w i th
about 3 . 5 m i n at ful l
power.
the test was
The reactor was
res ta rted o n May 20 and operated at fu l l
for
over
13 m i n.
It
was
restarted
power
aga i n
on
to
detenni ne
how the
The
fuel was the same as that u sed i n Phoebus-lA .
December 1 5 .
N RX-A6 tes t exceeds the NERVA
des i gn goal of 60 mi n at 1 100 MW i n a si ng l e run.
1 968
The tes t was termi nated by a spuri o u s tri p from
the turb i ne overspeed c i rc u i t.
for
45 mi n of wh ich 30 mi n , the maxi mum t i me p l anned ,
fast excursion to confi rm the analytical model s
Apri l
on
s uffi c i ent to permi t 30 m i n of conti nuous opera
1 965
Test )
operated
J u ne
nucl ear
26.
rocket
Phoebu s-2A ,
reactor
the
ever
1 2 . 5 m i n above 4000 MW .
most
bui l t ,
powerful
runs
for
The durati on o f the tes t
i n the l ow- to
w a s determi ned b y the avai l abl e cool ant supp l y .
medi um-power range to expl ore the l i mi ts of the
Desi gned for 5000 MW , the te st was l i mi ted to 80%
reactor operati ng map .
of ful l
May 28 and operated for 45 mi n
The total operati ng time
power beca u se the al umi num segments o f
of the reactor was 66 m i n wi th over 16 . 5 m i n at
t h e pre s s ure vessel
ful l power .
maturely .
J une 2 5 .
T h e a i ms of Ph oebus-lA , the fi rst
tes t of a new c l a s s of reacto r s , were to i ncreas e
the speci f i c i mpul se ,
the power den s i ty i n the
c l amp b a n d overheated pre
The reactor was res ta rted on J u l y 1 8
a nd operated at i ntermedi ate power l evel s .
December 4 .
c e s sful l y
Pewee reactor testi ng i s suc
comp l ete d .
Pewee,
des i gned
to
be
a
The tes t i s run suc
smal l tes t-bed reacto r , set records i n power den
c e s sful l y at ful l power ( 1 090 MW ) and core exit
s i ty and temperature by operati ng at 503 MW for
temperature ( 2370 K)
40 mi n at a cool ant ex i t temperature of 2550 K
3
and a core average power densi ty of 2340 MW/m •
core , and the power l evel .
was
subsequentl y
l i quid
for 10 . 5 mi n .
damaged
hydrogen
supply
when
wa s
The reactor
the
fac i l i ty's
exhau sted .
Thi s
Thi s power densi ty was 50 % greater than that re
course of events was i n no way rel ated to a ny
qui red for the 1 500-MW N E RVA reactor .
defect i n
power den s i ty i n the fuel
the
ful l - l ength ,
reactor .
1 9- ho l e ,
The core cons i sted
hexagonal
fuel
of
e l ements
l oaded wi th coated uc
parti c l e s .
The bores
2
were NbC c l ad by the chemi cal vapor depo s i t i o n
The N RX/EST ,
f i r s t N ERVA breadboard power pl ant,
the
i s operated
du ri ng 5 di fferent days for a total o f 1 h and
of
which
( 1 100-1 200 MW ) .
greatest
achi eved
28 mi n
These
by
were
time s
a
at
were
s i ng l e
ful l
by
nucl ear
power
ful l
6
X E ' , the fi rst down-fi ri ng prototype
at 1 100 MW .
i s succe s sful l y operated
The reactor was operated at vari o u s
power 1 evel s on di fferent days f o r a total
of
1 1 5 mi n o f power operati on that i ncl uded 28 re
s tarts .
Indi vi dual
times were 1 i mi ted by
test
the fac i l i ty ' s water storage system , whi ch coul d
rocket
not support operations l o nger than about 10 m i n
a t ful l
N RX -A5 i s operated successfu l l y at
power for 1 5 . 5 mi n .
The core conta i ned
the
far
reactor as of that date .
J u ne 8 .
spec i f i c i mpul se o f 845 s.
the same type of fuel el ements a s Phoebus-lA .
n ucl ear rocket eng i ne ,
1966
February 3 to March 2 5 .
50 m i n ,
c ool ant exi t temperature corresponds to a vacuum
Ma rc h .
(CVD) proces s .
The peak
3
was 5200 MW/m .
The
I t was resta rted and
reactor power .
s i gni ficant
mi 1 es tone
Thi s te st seri e s was a
in
the
nuc l ear
rocket
program and demonstrated the feas i bi l i ty of the
engi ne l ongev i ty ( i n i ti al l y 1 h,
NERVA concept .
was necessary to mi nimi ze hydrogen corro s i on of
In th i s yea r , the producti on of the chemi cal
rocket Saturn V
was
s u spende d .
It
woul d
have
O n l y a few materi al s ,
(ll)
a n d graph
t i ona l and thermal stre s s .
the
refractory
metal s
i te , a re s u i tabl e for u se in reactors desi gned to
1972
NF - 1
and breakage of the core from vi bra
i ncl udi ng
been the pri me l au nch vehi c l e for N E RVA .
June 1.
the fuel
then 10 h ) , i t
tes t i s
succes sful l y accom
run
at
h i gh
temperatures
( up
to
2700- 2 800 K ) .
pl i shed .
The reactor was operated for 109 mi n at
Graph i te was sel ected because i n contra st to the
the
desi gn
metal s , it i s not a strong neutron absorbe r , and
ful l
power of
44 MW,
demonstrati ng
fuel performance at a cool ant ex i t temperatu re to
it does moderate neutrons l eadi ng to a reactor
250 0 K and a near- record peak power den s i ty i n
3
the foe l o f 4500-5000 MW/m . N F - 1 was des i gned
w i th a
smal l er cri ti cal
n i um .
Graph i te
wi th a remotel y repl aceabl e core i n a reusabl e
strength , but i ts great di sadvantage i s that i t
test bed , i ntended as an i nexpen s i ve approach to
reacts wi th hot hydrogen to form gaseous hydro
mul ti pl e testi ng of advanced fuel materi al s and
carbo n s and , unl e s s i t i s protecte d , i t rapi dl y
structures.
Another speci al feature of th i s test
erode s .
seri e s
eval uati o n
wa s
c l eanup system.
in
removi ng
of
a
reactor
effl uent
The sy stem performed a s expected
radi oacti ve
contami nants
from
the
and the pure ( U , Zr ) C carbi de fuel ,
were tested i n NF - 1 .
1 enges
J anua ry .
succe s s ,
It
was
changi ng
j udged
a
nati onal
technical
pri o ri ti e s
res u l ted i n the deci s i o n t o cancel the program .
As shown
consi sts
of
turbopump
a
to
rocket
of
program
adequate
was
to
l i fetime
in
had to cons i de r many factors such a s neutro n i c
and
heat-removal
requi rements ;
h i gh
mech ani cal
schematical l y i n Fi g . 1 1 ,
c ryogen i c
feed
the
pro pel l ant
propel l ant
tank ,
th rough
it
a
the
To perm i t prel i m
i na ry eval uati on of the neutro n i c cal cul ati o n s , a
mockup or cri tical a s sembly of each reactor type,
k nown
a s Honeycom b ,
(l4,l5l
It
Fig. 12.
l ate
REACTOR DEVE LOPMENT
The concept of a nucl ear rocket eng i ne i s
s i mpl e .
nucl ear
e l ements
hi gh-pre s s u re hot hydroge n .
s l ab s ,
III.
the
fuel
control , shutdown, and safety .
The Rover nuc l ear rocket program
but
of
l oadi ngs ; and the comp l ex probl ems of sta rtup ,
1973
termi nated .
h i gh- temperature
The desi gners o f the nucl ear rocket e ng i ne
Two typ e s o f fuel el ement s , ( UC - Z rC )C "com
is
excel l en t
u ra
Con sequentl y , one o f the greatest chal -
devel op
e ffl uent reactor gas.
p os i te" fuel
has
mass of enri ched
was
bui l t
consi sted
as
shown
of
in
graph i te
enriched u ran i um foi l s , pl astic to s i mu
the
b l oc k s .
propel l an t ,
Later,
and
beryl l i um-refl ector
du ring constructi on of each new
type of reactor, a more exact mockup of the f i na l
reactor,
k nown a s Zepo ( Zero Power) , w a s bui l t
( Fi g . 1 3 ) u s i ng actual fuel el ements to dete rmi n e
system, a nuclear reactor to heat the pro pel l ant
t h e sy stem ' s neutroni c s .
to the h i ghest temperature poss i bl e , and a th ru s t
were bui l t at Los Al amos and WAN L .
nozzl e through wh i ch
reactor and engi ne te sts were carried out at the
the h o t g a s
is
expanded .
The propel l ant i s hydrogen becau se a gas wi th the
l owest- p o s s i bl e
mol ecul ar
wei ght
is
chal l enge
reactor
presented a real
desi gn
and
materi al s
devel opmen t .
The c o re exi t temperatu re of the
cool ant
to
had
h i ghest- possi bl e
power
NRDS .
A.
in
den s i ty
be
maximi zed
spec i fi c
al so
had
m i n imize reactor ma s s .
to
achi eve
i mpul se.
to
be
The
maxi mi zed
The actual
most
desi rabl e .
T h e reactor des i gn goal s
Such testi ng faci l i ti es
the
core
to
To ach i eve a practical
Ki wi - A
The
fi rst
reactor
tested
program wa s named K i wi - A .
bui l t by Los Al amo s
seri e s of reacto r s .
u nder
the
Ro ver
It was desi gned and
as were
al l
of
the Kiwi
( l6 l
as
The reactor des i gn ,
s hown i n F i g . 1 4 , was i ntended to produce about
100 MW of powe r .
5 m i n at 70 MW .
It wa s ,
i n fac t ,
tested for
The Kiwi-A core consi sted of an
7
annul a r stack of four axi al l ayers of fl a t-pl ate ,
shattered and wa s ej ected out of the nozzle a l ong
graph i te fuel el ements
w i th the graph i te wool between the center i sl and
ri ched
uo
reta i ned
l oaded wi th
h i ghly
en
parti c l e s .
The fuel el ements were
2
and supported i n graphi te struc tures
cal l ed whi m s .
The whi m s , shown in F i g . 1 5 , were
a nd the core .
to conta i n
The functions o f th i s p l ate were
the c a rbon
wool
i n sulation
and
to
serve as a gas seal that prevented gas from by
wheel l i k e structures wi th 12 wedge-shaped boxes
passi ng
the
o f fuel p l ates fi tted between thei r spok e s , each
reg i o n .
F a i l ure of the c l o sure p l ate all owed a
box conta i n i ng 20 fuel p l ate s .
l ot of gas to fl ow radi al ly i nward through sl ots
A fi fth wh i m con
annular
core
i nto
tai ned u n l oaded fuel p l ates and served a s an end
i n the i n s i de wal l of the wh i ms
refl ector for the outlet end of the core .
i nto the central
The
the
central
(Fig. 15)
and
p a rt of the core , thereby by
i nl et a nd radi al refl ectors consi sted of several
passi ng the power-produc i ng regi on of the core .
conti nuous graph i te cyli nder s .
Th i s bypassed gas was not heated to ful l tempera
Power flatteni ng
was ach i eved by vary i ng the fuel
l oadi n g .
The
ture .
Because
the
pre scri bed
The hole i n the center o f
fol l ows that the gas that d i d pass through the
the core conta i n e d a "o o i sl and , " the functi o n
2
wh i ch wa s t o moderate neutron s , thereby
235
reduc i ng the critical mas s of
u, a nd al so to
acti ve co re had to be heated to a h i gher tempera
prov i de a l ow-temperature , low-pressure contai ner
ture .
The h i gh fuel
outl e t
temperatu re ,
a
carbon wool
of
gas
demanded
core was separated from the radi al refl ector by a
reg i o n .
average
test condi tions
it
temperatures that resulted
l ed to mel ti ng of the uc
2
of the graphi te fuel pl ate s .
fuel and h i gh e ro s i on
reactor control rods that were cooled by
F o r the next two reactors, the K i wi -A core
ci rcul ating o o .
The enti re reactor was e n
2
c ased i n a n alumi num pre s sure shell t o w h i c h a
des i gn was modi fied to replace the whims and fuel
for the
li ght-water-cool ed
n i ckel
nozzl e
wa s
attached .
pl ates wi th graphi te modu l e s contai ni ng cyli ndri
1 18)
cal fuel elements
a s s hown i n F i gs. 1 6 and
The nozzl e was desi gned for choked- fl ow outl et
17.
condi tions for the core cool ant ( that i s , son i c
i n the fuel fabri cati on proc e s s from pressi ng and
fl ow at the th roat of the nozzle).
mol di ng to a new graphi te extru s i on proces s .
The
hydrogen
cool ant
reactor i s a s follows .
fl ow
through
the
Coolant is deli vered to
fuel
Thi s modi fi cati on e ntai l ed a compl ete change
cyl i nders we re segmented
in
The
short l ength s
and s i x of them were stacked on top of each other
the plenum near the top of the pressu re ves se l .
in each hol e of the graphi te modu l e s to make up a
The gas then fl ows a x i al l y downward through h o l e s
compl ete fuel modul e .
The fuel
cyl i nders con
i n the refl ector segments a nd i nto the p l enum a t
tai ned four ax i a l cool ant channel hol e s tha t were
the bottom o f the pre ssure ve ssel where the fl ow
c oated by a CVO process wi th N bC to reduce hydro
reverse s ,
passi ng
i nl et refl ector.
upward
th rou gh
hol es
in
the
The gas now conti nues upward
between the fuel p l ates of each wh i m , th rough the
unl oaded p l ate s of the top whi m , and out th rough
of
Kiwi-A
6 mi n
experiment
was
a
fi rst
step
test s ,
temperature , gas-cooled reactor for nuc l ear pro
though
severe corro s i on .
as
such
it
provi ded
reactor des i gn and materi als i nformati o n .
i mportant
1 8 •1 7 )
Much h i ghe r fuel temperatu res ( up t o 2 900 K )
plate ,
anti c i pated were
8
l ocated
modi f i e d
for
5
but the general appearance of the
pul s i o n ,
than
Th i s
twi ce
to
i n the p ower range 85- 100 MW i n the
20
l g)
and K i w i - A3 ( l tests .
Fracture
elements
because early
graphi te .
Kiwi - A ' (
toward demonstrati ng the fea s i b i l i ty o f a h i gh
and
the
of fuel modules was experi enced i n both o f these
the n ozzle .
The
gen corro s i o n
core confi guration w a s tested
in
reached duri ng
the run the graph i te
j u st
above
the
o o
2
the
test
The
a fter each test was
several
K i wi -A
elements
seri es
qui te
showed
of
bl i steri ng
tests
fuel
good even
121l
and
demon
strated that hydrogen gas could be heated i n a
n ucl ear reactor to the temperatures requi red for
cl osu re
space propul s i o n and that such a reactor coul d
i sl and,
i ndeed be control l ed .
B.
cool ant channel ,
K i w i - B and N RX
Bui l t
Kiwi-A
on
the
reacto r s ,
experi ence
a
gai ned
new reactor
wi th
des i gn
the
evol ved
s i zed to provi de approxi mate l y
t h e same exi t gas temperature f o r al l c h annel s .
The
core ,
wh i ch
c ontai ned
1 82 k g
of
u ran i um
that more nearl y resembl ed what wou l d be needed
( enri chment 0 . 9 3 15 ) , wa s su rrounded by a graph i te
for a fl i ght e ng i n e .
cyl i nder
about
46 mm th i ck
refl ector
1 1 4 mm
th i c k .
i n i ti ated
wi th
the
The Kiwi -B test series wa s
22 }
Kiwi -BlA (
test
in
December 196 1 and c u l mi nated 2 yea rs and 8 months
1 ocated
l ater w i th the successful
boron
p l i shed i n August 1 96 4 .
i mprovements
were
K i wi-B4E
test accom
Duri ng th i s test seri e s ,
made w i th
the
extruded
fuel
and
Twel ve
a
bery l l i um
rotati ng
drums
in the refl ector contai ned segments of
carb i de
neutron
absorber
that
coul d
be
swung toward o r away from the core to provi de
reacti v i ty control
Severe structural damage to the core was experi
ve ssel to which th e exhaust nozzl e was attache d .
enced
The
wi th the second test i n the seri e s
2 3>
when the h o t ends o f seven fuel
modul e s were ejected from the core duri ng
tran s i ent ri se to ful 1
the
ful l -power
tes t s ,
( 24 • 2 5 }
a n d several
pa rti cul a r
col dfl ow
K i w i -B4D ,
pressu re
in
vessel
an
wa s
al umi num
pressure
approximate l y
21
nm
th i ck , 1 . 9 m i n l ength, and 1 . 3 m i n outer di am
eter .
I t took several
in
subsequent
K i w i - B4A,
power.
enca sed
The enti re
reac tor
(
( Kiwi-B1B }
was
of the reactor.
desi gn and the protec ti ve NbC-coati ng technol ogy .
T h e fl ow o f hy drogen cool ant
reactor was as fol l ow s ( F i g . 3 ) :
through
the
l i qu i d hydrogen
entered the aft end of the nozzl e to cool
the
tests to di scover and confi rm that core damage
nozzl e wal l befo re enteri ng the refl ector p l enum .
was
F rom th i s p l enum the
caused
by
demonstrate ,
fl ow- i nduced
afte r
desi gn
v i b rati ons
and
modi fi cati ons
to
were
through
the
hy drogen trave l ed forward
refl ector
and c ontrol
drum s ,
appl i e d , that a stabl e desi gn had been ach i eve d .
c ool i ng the pre ssure ve ssel .
Th i s
agai n before fl owi ng forward through
reactor
successful
confi gu rati o n
( 2 6- 30 l l ed to t h e N RX seri e s ( 6 } o f
( K iw i -B4E )
N E RVA devel opmental
Fig . 3 .
reactors from wh i ch emerged
3 1 •3 2 }
shown earl i e r i n
N RX -6 des i gn (
the fi nal
The reactor wa s desi gned for a nomi nal
p ower o f 1 100 MW .
I t wa s al l graph i te moderated ,
and i t had an epi thermal neutron spectrum.
extruded graph i te
fuel
The
e l ements were hexagonal
and contai ned 19 cool i ng channel s .
The channel
wal l s and the exter i o r surfaces of the fuel el e
re gion of the s i mul ated sh i el d .
reg i o n between the s h i el d and the dome
pressu re vessel .
core
support pl ate .
The t i e rod
Mos t o f the cool ant the n
fl owed through the channel s i n t h e f u e l el ements
where it was heated to a h i gh
smal l
six el ements supported by a tie rod in the cen
Here the fl ow reversed , and the
shi el d , then through a fi ne mesh screen and the
reg i o n
tral l ocati on a s shown in Fi g . 1 8 .
of the
gas fl owed aft through the i nner reg i o n o f the
ros i on .
was a s sembl ed i n c l usters of
the outer
The fl ow d i s
cha rged from the s h i el d and entered the p l enum
ment were coated wi th NbC to reduce hydrogen cor
The fuel
al so
I t entered a pl enum
part
of
between
the
fl ow
the
core
temperature .
A
cool ed
the
peri phery
a nd
the
bery l l i um
refl ector, and some cool ant al so fl owed past the
t i e rods i n the core .
These cool ant fl ows were
wa s attached to an al umi num support pl ate at th e
mixed in the nozzl e chani>er at the reactor exi t
col d
before expul s i on th rough the nozzl e .
end
of
the
reactor.
I rregu l arly
shaped
c l usters were fi tted o n the core peri phery
obta i n
a
cyl i ndri cal
core
confi gurati on.
to
One aim o f the devel opmental seri e s o f tests
The
c onducted by Westi nghouse E l ectri c was to reduce
core dimen s i o n s were 1 . 3 2 m i n l ength and ap prox
the frac tion of coo l ant fl ow that d i d not p a s s
i mately 0 . 89 m in d i ameter.
through the fuel i n order t o obta i n the h i ghest
La teral support fo r
the core wa s obtai ned wi th a spri ng a nd a ri ng
possi b l e gas temperature i n the nozz l e chamber .
seal arrangement a s descri bed i n Fi g . 1 9 .
Thi s a i m was achi eved by applyi ng des i g n mod i f i -
fl atteni ng
l oadi ng ,
was
achi eved
by
vary i ng
the
Power
fuel
and the c ool ant fl ow di stri buti on was
colltrol l ed by orifices i n the i nl et end of each
cati ons
reactors .
descri b ed
bel ow
for
the
Phoebu s
The duration of ful l - p ower runs was
gradual l y i ncreased wi th each N RX reactor unti 1
9
the tes t i n December 1967 i n wh i ch the N RX-A6 ran
The
reactor (
Phoebus-2A
4o-4 2 l
i ncorporated
conti nuous l y for 60 mi n at 1 1 2 5 MW w i th an exit
al l of the features mentioned above .
cool ant temperature at o r above 2280 K,
which
spondi n9 to
7 30 s. ( 33-3 5 l
l evel
a
vacuum
The
spec i fi c
tes t
corre
i mp u l se
durati on
and
exceeded the N ERVA des i gn goal s
of
power
at
that
t i me .
conta i ned about 300 kg
of
The core ,
u ra n i um ,
con
s i sted of 4068 fuel ed el ements p l u s 7 2 1 regenera
ti vely cool ed support el ements.
The active core
dimen s i ons were 1 . 39 m i n di ameter and 1 . 3 2 m i n
l ength .
The 19-hol e fuel e l ements were s i mi l ar
i n geometry a nd h ad the same external dimen s i on s
C.
Phoeb u s
Fo1 1owi ng the successful perf ormance of the
as
those
N RX -A6 ) ,
of
earl i e r
but
the
reactors
( K i wi -B4E
to
di ameter
was
cool ant channel
K i w i -B4E reactor , the Los Al amos Sc i enti f i c Labo
i ncreased from 2 . 54 mm to 2 . 7 9
ratory devoted i ts attenti o n to a new c l a s s of
were coated wi th
reactors s i mi l a r in de si gn to Ki w i -B but havi ng
were overcoated wi th a 1ayer of Mo to
greater cool ant exi t temperature s , power den s i
hy drogen corro s i on o f the graph i te .
ti e s, a n d power l evel s .
the fuel was a ssembl ed i n c l u s ters of seven el e
Power den s i ty w a s to b e
i ncreased mai nl y by enl arg i ng t h e di ameter of the
coo1 ant fl ow channe 1 s i n the fue1 e1 ements from
2 . 54 mm to 2 . 7 9 mm to reduce thermal
core press u re drop .
stre s s and
The temperature i ncrease was
to be obtai ned by some mi nor desi gn modi fications
ments
where
NbC
the
central
graphi te conta i ni ng
a ssembly .
fl ow
Detai l s
paths
for
the
of
the
e l ement
in the fuel el ements b u t mostly by reduc i ng the
i nterface
had
a s sembly
that
an
was
construction
u n l oaded
a l umi num
support
and cool ant
regenerati vely
separated
and
reduce
As before ,
ti e-tube axi a l
tubes are shown i n F i g . 2 1 .
amount o f cool ant f l ow that bypas sed the core .
The channel s
nm.
of tapered th i ckness
cool ed
ti e
The core- refl ector
i nterface
the
cyl i nder
h i gh-pre s su re
The cool ant fl ow a l o ng the core peri phery wa s
refl ector system reg i o n from the 1 ower- pressure
reduced , and the s i ngl e-p a s s cool i ng of the metal
c ore peri phe ry ,
changed
by
ri ng s .
Th i s
These
bypa s s
cool ant.
t i e rods i n the core was reduced and eventua11 y
to
two-pass
regenerati ve
cool i ng
rep l ac i ng the t i e rods wi th t i e tube s .
transmi tted the axial
pressure
drop 1 oad to the nozzl e , and contai ned the sea1
as sembly w a s cool ed
The
refl ector
the core support a nd retu rni ng thi s fl ow to the
rather than 1 2 as used for the earl i e r smal l er
These
el emen t s .
cool ant
fl ow
mod i fi cati ons
reactors.
contai ned
18
refl ector
bery l l i um-
tubes were cool ed by di verti ng 10% o f the fl ow to
mai n core cool ant fl ow at the i nl et o f the fuel
a s sembly
by
203-mm-thi ck
control
drums
The reactor was conta i ned in an a l umi
num pre s s u re vessel
2 . 54
nm
th i c k w i th an out
greatly reduced the mi x i ng of col d cool ant wi th
s i de di ameter of 2 . 07 m and an approx imate l ength
the core exi t gas i n the nozzl e chamber.
( exc l udi ng the nozzl e )
p ower l evel
The
was i ncreased s i mp l y by i ncreas i ng
i ncl udi ng
the
pre s s u re
vessel
9300 kg .
The
Fi g . 22 .
fi rst two
for
adj usti ng two b a s i c parameters, namely , the c oo l
tests were
experiments
l eadi ng
e s senti al l y
to
the
veh i cl e s
Phoeb u s-2A
des i g n .
Reactor
reactor
A
and - 2A , were carri ed out i n th i s s e ri e s .
neutron i c
the
was
two-dimensi onal
in
of
Reactor mas s
the n umber of fuel el ements i n the core .
3 6l
( 3 7-39 l
Three
tests ,
Phoebu s - lA , (
- lB ,
u sed
model
o f 2 . 5 m.
cal cul ati ons
control
was
is
that was
s hown
in
obtai ned
by
a n t fl ow rate and the control - drum posi ti o n .
Phoebus-2A ( F i g . 20 ) desi gned for 5000 MW was the
The s uccessful ful l - power test o f Phoebus-2A
mos t powerful nucl ear rocket reactor ever bui l t .
took pl ace i n J ul y 1968 and l as ted for 1 2 . 5 mi n ,
I t was
i ntended o ri gi nal l y
opti mum-thrust
nucl ear
amb i ti ou s p l anetary mi s s i on s .
nomi nal
spec i fi c
thrust of
i mpul s e
1 1 10 kN
of
to
be
840 s ,
a
prototype
a time 1 i mi ted by the avai l abl e hy drogen cool ant
for
supply ( cool a n t , dri ven by two Rocketdyne Mark-25
The reactor had a
turbopumps operati ng in paral l el , fl owed through
propul s i on
engi ne
( 2 50 000 l bf )
correspondi ng
nozzl e chamber temperature of 2500 K .
and
to
a
the reactor at a rate of 1 20 kg/ s l .
a
power l evel reached duri ng the test was 4080 MW .
The maximum
The reactor coul d not be operated up to the
desi g n power l evel o f 5000 MW because part of the
10
al umi num pressu re vessel a ssembly was overheati ng
toward
prematurely as a res ul t of unexpected poor ther
and structural envi ronment for the fuel el ements
mal contact wi th an LH -cool ed cl amp ri ng .
2
maximum fuel -el ement exi t-gas temperature
The
i n a core contai ni ng one- fourth
the number of
a t
el ements
one-tenth
tai ne d was 2 3 10 K , and the maximum nozzl e chamber
temperature ,
nearl y a s
h i g h , was 2260 K .
provi di ng
in
a
these
real i st i c
reactors,
nucl ear ,
and
thermal ,
the
number of el ements i n Phoebus-2A .
Thi s
Mo st of the bas i c des i gn features of Pewee
smal l temperature d i fference i s an i ndi cation of
were s i mi l ar to those of the precedi ng reactors.
the effecti veness of the measures taken to reduce
The fuel
m i x i ng o f col d cool ant wi th the core exit gas.
hel d i n pl ace by s upport e l ements ;
At des i gn power ,
h ave
been
the core power dens i ty woul d
nearly
twi ce
that
of
the
Ki wi -B
The Phoebus-2A test reveal ed some neutro n i c
d i screpanc i e s w h e n c ompared wi th pretest cal cul ations
and
43 ,44 >
zero-power
cri tical i ty
Spec i fi cal l y ,
experi -
the
ful l - scal e
l a rger
a nd they were
the control
drums were i nc o rporated i n the beryl l i um rad i a l
refl ector; a n d l i qu i d hydrogen w a s u s e d a s the
work i ng fl ui d .
reactor s .
ments. (
el ements were simi l a r ,
There were , however , s i gni ficant
d i fferences that d i sti ngui shed Pewee from earl i e r
reacto r s .
T h e core
di ameter w a s
reduced
1 400 mm i n Phoebus-2A to 533 mm to
n umber of fuel
el ements.
from
reduce
the
Suffi c i ent reacti vi ty
col d-to-hot
wi th the smal l er core was obtai ned by i n se rti ng
c h anges i n reacti v i ty than had been predicted .
s l eeves of zi rconi um hy dri de around the t i e rods
The anomal i e s were
in the support el ements a s shown i n Fi g . 2 3 .
reactor
tes t
resul ted
in
eventual l y resol ved and a t
The
l ow
hy drogenous materi al moderated the core neutrons
b e ry l l i um-refl ector temperatures and the pre sence
and reduced the cri tical mass of urani um i n the
o f col d h i gh-den s i ty
core to 36 . 4 kg .
tri buted mai nl y to the comb i ned effect of
hy drogen
in
the
al umi num
The ratio of support el ements
The
to fuel el ements was i ncreased from 1 : 6 to 1 : 3 ,
re sul t was to produce a l arge negati ve change i n
a s i l l u strated i n F i g . 2 4 , to i ncrease the amount
reacti v i ty and a substanti al
of Z rH
i nterface cyl i nder
tro l - drum wo rth .
and
in
the
refl ecto r .
reducti on
i n con
Nei ther o f these effects had
been c orrectly accounted for i n pretest analysi s .
The successful concl u s i o n of the Phoebus- 2A
tests was a m i l es tone i n
nucl ear rocket tech
moderator to the desi red l evel .
Thi s
x
el imi nated the tradi ti onal cl usters-of- seven con
c ept; each fuel e l ement was s upported redundantly
by two pedestal s .
The core contai ned 402 fuel
el ements and 132 s upport el ements.
Because Pewee
nol ogy because of the h i gh-power capabi l i ty tha t
wa s desi gned as a test bed for fuel el eme n t s , n o
t h e test demonstrate d .
a ttempt w a s made t o maximi ze the spec i fi c i mpul se
Some probl ems rema i ne d ,
pa rti cul arly i n the area o f f u e l
temperature capabi l i ty ,
l o ngev i ty and
but the feasi bi l i ty of
by ma i ntai ni ng a h i gh temperature i n the nozzl e
c h amber ;
the
support-el ement
cool ant
was
di s
Th i s
di s
practical nuc l ea r space propu l s i on had been con
cha rged di rec tl y
v i nc i ngly demonstrated by th i s s tage o f the Rover
ch arge
program .
Phoeb u s - 2A was the l as t reactor des i gn
i cantly becau s e the hydri de moderator requi red a
i n d i rect support of the NERVA devel opment that
l arg er amount of cool ant than a graph i te support
wa s tested by Los Al amo s .
el ement
Two smal l er reactor
reduced
wi thout
i nto
the
the chamber .
nozzl e
moderator
temperature
and
because
s i gni f
a
con
designs were s ubsequently tested by Lo s Al amo s ,
servati vel y l ow cool ant di scharge temperature was
but they were prima ri l y te st beds f o r improvi ng
chose n .
the fuel technol ogy .
The
( 205-mm)
D.
Pewee
Pewee
( 45 l
smal l
reactor desi gned to
pl aced
designs.
a nd N RX
The
fuel
general
el ements
des i gn
was
and
other
di rected
th i c k
The
i nner part consi sted o f beryl l i um ri ngs that re
size
components.
s i ze o f Pewee requi red a
two concentri c parts a s shown i n F i g . 2 5 .
was a
serve as a tes t bed for the eval uati on of ful l
Phoebus
smal l
beryl l i um refl ector that w a s bui l t i n
the
i nterface
cyl i nder
of
prev i ou s
The outer part was made from Phoebus-1-
type sectors and contai ned ni ne control
drum s .
11
The mass
of
the
Pewee
reactor ,
i ncl udi ng
the
Pewee
test
seri es
I t was never meant
to be a c andi date concept for a rocket engi ne .
alumi num pressure vessel, was 2 5 70 kg .
The
havi ng a l ow fuel i nventory .
conducted
in
November-December 1 968 wa s succes sfu l , and i t set
several records for nucl ear rocket reacto r s .
The
prima ry objecti ve was to demonstrate the capabi l
The reactor, descri bed i n F i gs. 26 and 2 7 , con
s i sted of two parts :
tion
that
a permanent, reusabl e por
i ncl uded
s tructu re ;
and
a
the
refl ector
tempora ry ,
and
external
removable
p o rt i o n
i ty of th i s new reactor as a fuel -el ement test
that consi sted of t h e core assembly a n d a sso
bed .
ci ated component s .
Pewee ran for a total of 192 min at power
The
A maj or objecti ve o f th i s desi gn w a s t o have
ful l -power test consi sted of two 20-m i n hol d s at
a reusable test devi c e that woul d reduce both the
des i gn power ( 503 MW) and an average fuel -element
t i me between reactor tests and the cost of test
level s
above
1 MW
on
two
separate
exi t-gas temperature of 2550 K.
day s .
Th i s temperatu re
i ng .
After compl eti on of a te st seri e s , the core
was the h i ghest ach i eved i n the Rover program .
a s sembly woul d be removed and d i sassembl ed for
It corresponds to a vacuum spec i f i c impul se o f
exami nati o n ,
8 4 5 s , a l evel i n excess of the de s i gn g o a l s e t
woul d
for the N E RVA .
Actual l y , the N F - 1 was tested only once before
T h e p e a k f u e l temperature al so
reached a record level of 2750 K.
The average
3
power densi ty i n the core wa s 2340 MW/m , al so
be
whereas
re tai ned
termi nat i o n o f
the
for
the
permanent
use
wi th
program ,
s tructure
a
but
new
the
core .
removabl e
feature of the design was demonstrated .
The
a record h i gh and greater than that requi red for
NF -1
core
wa s
a
34-cm-di ameter
by
1 46-cm- l ong al umi num c a n that c onta i ned 49 fuel
the NERVA . The peak power densi ty i n the fuel
3
was 5200 MW/m . The fuel e l ements were s i mi l ar
e l ements as compared to 402 in Pewee.
to those of Phoebu s - lA except for a few elements
was surrounded by a 2 7-cm-th i ck beryl l i um radi a l
CVD-c oated w i th ZrC
re fl ector th at accommodated s i x rotati ng control
coated
fuel
i n stead of NbC .
el ements
p e rformed
The
ZrC
si gni fi cantl y
better.
The reactor performed cl ose to des i gn c ond i
t i ons except for a n
u nexpec ted ,
l a rg e ,
rad i a l
drum s .
The
fuel
u rani um
( 9 3 % enri ched) .
heterogeneous
Each
refl ecto r
p ower .
14%
But
a
greater
the
heat
than
p i ck up
in
the
predi cted
at
ful l
s uccessful performance
Pewee reactor des i gn was
important
of
the
because
it
about
Suffi c i ent
5 kg
of
reacti v i ty
i nventory was obtai ned by des i g n i ng the core a s a
gas
and
was
for critical confi gurati o n wi th such a small fuel
vari ati on o f 2 20-310 K i n the fuel -element exi t
temperature
i nvento ry
Th i s core
fuel
water-moderated
cel l
hexagonal fuel
contai ned
a
thermal
reacto r .
standard
1 9- hol e ,
el ement encased
tube a s descri bed
in
F i g . 28.
in
an
al umi num
The cell tubes
were i n serted i ns i de al umi n um sl eeve s , and water
wi th
fl owed through the c ore i n two passes, fi rst be
the
tween the sl eeves and the eel l tubes to the aft
c ore , coul d be operated i n the configurati on and
end of the core , where the fl ow turned around and
in
went back between
demonstrated
that
smal l
reactors,
l ow-temperature moderati ng materi al s
the
rocket
extreme
eng i n e .
temperature
A
second
i n s i de
envi ronment
test
of
the
of
a
Pewee
c ool a n t ,
after
the el ements.
mak i ng
several
The
pa sses
reactor had been pl anned , but Pewee-2 was never
reflector assembl y , made a
s i ng l e p a s s
b ui l t .
the core wi thi n the fuel cool ant channels.
The hy drogen exhaust gas was
E.
ferently than in pre v i ou s reactors.
Nucl ea r Furnac e , N F - 1
through
a
in
the
through
handl ed di f
I n stead of
T h e l ast reactor test of t h e enti re Rover
46 4 7 )
program wa s that o f the N F - 1 , ( '
a reactor
bei ng
ten time s les s i n des i gn power than Pewe e .
gen was f i r s t cool ed by i nj ecti ng water di rectl y
The
exhausted
hydrogen
convergent- d i vergent
nozzl e d i rec tly to the atmosphere , the hot hy dro
NF-1 was devi sed to pro v i de an i nexpen s i ve means
i nto the exhaust gas stream as shown i n F i g . 2 9 .
of testi ng ful l -si ze nucl ear rocket reactor fuel
T h e resul ti ng mi xtu re of steam and hydrogen g a s
e l ements a nd other core components i n a reactor
was then ducted t o an effl uent cl eanup sys tern to
12
remove
fi s s i o n
products
before
rel ease
of
the
cl eaned gas to the atmo sphere .
The
prima ry
obj ecti ves
of
the
NF - 1
test
seri es were to veri fy the operati ng characteri s
fuel mel ti ng temperature was 2683 K, the mel ti ng
temperature o f the uc - c eutecti c .
2
The fuel p l ates for the ori gi nal
K i wi - A
reactor were mol ded and pre ssed at room tempera
ti cs o f the N F - 1 and associ ated fac i l i ti es and to
ture , then c u red to 2723 K .
operate at ful l power w i th a fuel -el ement exi t
coati ng to protect
gas temperature of 2440 K for at l east 90 mi n .
corrosi on.
Al l
el ements that were extruded and coate d , i ni ti a l l y
p rima ry objecti ves were attai ned duri ng the
test seri e s .
the
dynami c
A weal th o f data was obtai ned on
and
stati c
characteri sti c s
of
the
NF-1 and the faci l i ty , and no maj or NF-1 de s i g n
def i c i enc i e s were found .
of 44 MW and a fue1 -el ement exi t-gas temperatu re
approxi mately 2440 K
for
a
record
time
109 mi n and at or above 2220 K for 1 2 1 mi n .
maxi mum
exi t
2550 K .
Two new types
temperature
tested i n NF-1 .
reached
of
fuel
was
of
The
about
el ements were
( composi te) e l ements that compri sed 47 of the 49
( U , Zr ) C ( carb i de ) el ements.
peak
power
The carb i de el ements
3
of 4500 MW/m
den s i t i e s
but experi enced severe cracki ng .
were smal l
el ements
hol e .
These el ements
( 5 . 5 mm across the fl ats ) , hexagonal
wi th
a
s i ng l e
3-mm-di ameter
cool a nt
Rede s i g n , by reduc i ng the web th i ckness by
reactors
u sed
w i th NbC , t o reduce hydrogen c orro s i on .
fuel
T h e fuel
el ement for the early reactors through K i w i - B lB
were
extruded cyl i nders wi th
tai ned
fi rst
in
fi rst
Kiwi-B
des i gn
four,
then
The cyl i nders were con
graph i te modul es.
K i wi- B4A
i ntended
as
was
a
the
prototyp e
fl i ght reactor; and i t u sed 1 9-hol e , one- p i ece ,
hexagonal fuel el ements , 19
a cros s the fl ats.
mm
Thi s fuel e l ement s hape became the adopted stan
da rd for al l the rema i ni ng reactor desi g n s .
They were the ( U , Zr ) C graph i te
fuel cel l s in the core and two cel l s conta i ni ng
wi thstood
sub sequent
seven cool ant channel s .
The reactor wa s operated at the des i gn power
of
Al l
The p l ates had no
the carbon agai n s t hydrogen
The
K i w i - B4E
test
was
the
fi rst
use
of
coated
uc
p a rti c l e s
in
p l ace
of
uo
2
2
parti c l e s i n the fue l .
The maj or probl em wi th
oxi de-l oaded
fuel
back-reaction.
el ements
wa s
M i c rometer-s i ze
the
so-cal l ed
uc
particl es
2
a re extremel y reacti ve and rev e rt to oxi de in the
pre senc e o f ai r , parti cul arly h umi d a i r .
oxi de-carbi de-oxi de
reactions
Thus,
occurred
duri ng
each heati ng and storage cycl e , i ncl udi ng graphi
2 5 % , woul d substanti al l y decrease the temperatu re
tizi ng , coati ng , a nd reactor operati o n ; and each
gradi ents and reduce the crack i ng .
cycl e caused l o ss of carbon by CO gas e vol ution
The composi te
el ements wi thstood peak power den s i t i e s i n the
3
fuel of 4500-5000 MW/m
and achi eved better
and degraded the el ement.
corro s i on
the uc
viously
performance
in
the
than
wa s
standa rd ,
observed
pre
graphi te-matri x ,
Phoebus-type fuel el ement.
F.
Fuel Devel opmen t (
Dimensi onal
al so were noted i n stored e l ements.
changes
Oxi dation of
l oadi ng materi al caused the el eme nt to
2
swel l a s much a s 4% so that the fi nal d i mensi ons
coul d not be c ontro l l ed .
The sol uti on to th i s probl em was the i ntro
8)
ducti on of u c
T h e maj o r technol ogy
effort o f
the
program was expended on devel opi ng fuel s .
Rover
Al l of
l arger,
parti cl es that were consi derably
2
50- 1 50 µm d i ameter , a nd coated with
-25 µm o f pyrolyti c graph i te .
The fi rst coated
the K i wi reactors except the l a st one, Kiw i - B4E ,
pa rti cl es had a l ow-den s i ty pyrocarbon coat that
u sed
coul d
h i gh l y
enriched
matri x .
uo
2
fuel
in
a
graphi te
not
wi thstand
hi gh
temperature s .
At
The uo partic l e s i ze was 4 µm and the
2
3
p a rti cl e densi ty was about 10 . 9 g/cm . At h i gh
2 273 K , the u c core woul d mi grate through the
2
c oati ng , thus destroy i ng the protecti on agai nst
temperatu res ( 1873-2273 K ) duri ng processi ng , the
the
uo
ti z i ng
reacted wi th the c a rbon surroundi ng i t and
2
was c onverted to uc
wi th evol uti on of CO and
2
con sequent l oss o f carbon from the el ement. The
back-reac ti o n .
2 173 K .
temperature
Thi s
Consequentl y ,
had
to
temperature
be
the
hel d
gradual l y
graph i
l ower
at
i ncreased
w i th improved coated part i c l es to 2573 K .
Coated
13
p a rti c l e s
were
wi thstand
287 3 K
quently
beads
eventual l y devel oped
for 0 . 5 h .
l ed to
u sed
cool ed
the
i n co11111erc i a l
reacto r s .
Thi s
devel opment
that cou l d
work
of
subse
the temperature ( 2623 K ) at which the n i obi um i n
contact wi th c a rbon was converted to NbC .
TR ISO
fuel
Meanwhi l e , duri ng the K i wi - B te sti ng seri e s ,
h i gh-temperature
gas
the CVD technol ogy was i mprovi ng a n d becomi ng a
The coated parti c l e s
in
the
soph i sticated
nucl ear rocket engi ne were not i ntended a s a con
1 3 2 1 -mm- l ong ,
process
i n wh i ch
2 . 4-mm- di ameter
19
ful l - l ength ,
bores
coul d
be
tai nment for f i s s i on products, the pri nci pal re
coated wi th NbC tai l ored i n th i ck ne s s over the
qui rement i n conunerc i a l reacto r s , but to provi de
ful l l ength of the el ement s .
s tabi l i ty
e l ements for the reactors from P hoebus-lA through
duri ng
fuel -el ement
processi ng
and
And so al l the fuel
storage and to el imi nate reacti on wi th h um i d a i r
the l a st one , and i nc l udi ng the N RX
and coati ng gases.
reactors,
Coati ng
technol ogy
the Rover program .
evol ved
As
greatly
menti oned
duri ng
earl i er,
the
were
CVD
coated .
seri e s of
The
earl y
CVD
coati ngs had a u seful 1 i fe o f about 10 mi n , but
by the end o f the program , NbC and ZrC c oati ng s
fuel el ements of al l the reactors tested i n the
had been tested for as l ong as 5 h .
program , except for K iwi-A, were coated w i th NbC
the fi rst nucl ear test to empl oy s ome fuel el e
( or ZrC l ate i n the program) to reduce hydrogen
ments coated w i th ZrC .
corro s i on .
It
had
been
hydrogen and graph i te ,
real i zed
early
that
at the anti c i pated h i gh
temperatures of a rocket e ng i n e , woul d react to
Pewee was
They performed s i gni f
i cantl y better than e 1 ements w i th NbC .
The pro
gre ss i ve improvements achi eved i n fuel
perform
a nce duri ng the NRX and Pewee seri e s of tests a re
form me thane , acety l ene , and other hydrocarbon s .
shown
F u rther,
terms o f mass l os s h a s been normal i zed to one for
sion
the graph i te l os s from hydrogen c orro
duri ng
reactor
operati on
a ffect the reactor neutro n i c s .
coati ng effort was
K i wi -A '
reactor
wou l d
seri ously
So a fuel -el ement
undertaken i n 1 959 for
to
devel op
thi n
the
( 0 . 025- to
0 . 05-mm-th i c k ) NbC o r ZrC coati ngs to act as a
i n Fi g .
30 , where corrosi on measured
the N RX-A2 and -A3 tes t s .
fue l - e l ement
des i g n ,
No maj o r change
fabri cati on
method,
characteri s t i c s occu rred i n the N RX seri e s .
in
in
or
The
e l ements were
al l made from coated uc
beads
2
di spersed i n a graphi te matri x , extruded wi th 1 9
barri er to hydrogen attack for the l ength of ti me
c ool ant channel s i n a hexagonal pri sm , and coated
the reactors were to operate .
wi th N bC .
Ni obi um carbide
The mai n contri bu ti ng factors for the
was sel ected i ni ti al l y because it has a hi gher
i mprovements were the use i n NRX -A6 of a Mo metal
eutec ti c temperature
overcoat over the N bC bore coat i n the fi rst 1 -m
does ZrC
shi fted
( 3 1 23 K ) .
to
graph i te
ZrC
( 3523 K ) wi th carbon than
Much l ater, attention was
because
and was more
it
adhe red
better
to
desi rabl e neutroni cal l y .
l ength of the el ements ( th i s o verc oat reduced the
mi dband corros i o n , wh i ch wi l l be di scussed bel ow ,
by
a
factor
of
10 ) ;
the
use
of
thi nner
NbC
wi th
CVD
coati ng s , wh i ch reduced thei r tendency to crac k ;
tech ni ques for the fuel el ements in Ki wi - A '
and
t i ghter control o f processi ng a n d ti ghter control
2 1 6-mm
of the fuel -el emen t external dimen s i o n s to reduce
The
-A3 .
coati ngs
These fuel
cyl i nders
nel s .
were
app l i ed
i ni ti a l l y
el ements we re
conta i n i ng
four
s h o rt :
axi al
cool ant
chan
The cyl i nders were desi gned to nest i nto
i ntersti ti al
gaps
between
el ements ;
a dj u s tments
i n fl ow ori f i c i ng and fuel l oadi ng to i mprove the
one a nother end to end to bui l d up the total el e
radi al
power and temperature profi l e acros s the
ment
core .
The corrosi on at the end of the N RX seri e s
l ength.
The
Kiwi-B
el ements
were
much
l onger, and CVD depo s i t i o n of NbC on fuel -el ement
was reduced to 30% o f that a t the begi nni ng of
bores had not devel oped to the poi nt where they
the
coul d be coated
Pewee-2 ,
s uccessful l y
and reproduc i b l y .
Consequentl y , a di fferent cl addi ng techni que wa s
N RX
seri e s ,
wh i ch
and
was
i mprovements
never
bui 1 t,
p l anned
for
wou l d
have
reduced th i s to 10% .
th i s
Much of the fuel testi ng was done i n a hot
techni que was to i nsert n i ob i um tubes i nto the
gas te st furnac e , wh i ch s imul ated the operati ng
fuel -el ement bores and heat the l i ned el ements to
condi t i o n s ,
u sed for these
14
reactors.
S i mply
s tate d ,
wi thout
radi ati on,
of
the
nucl ear
reacto r s .
The
hi gh- p ressure
furnace ,
whi ch
is
an attempt t o reduce mi dband corro s i o n . (
4 a , 49l
shown i n F i g . 3 1 , provi ded a reasonabl e simul a
The structure o f the compos i te fuel
tion o f reactor power den si ty ,
to that o f the standard gr a phi te-matri x fuel
temperature and
thermal s tre s s , and the effects of fl owi ng hydro
F i g . 33.
coated { U , Zr ) C particl es i n such a way as to form
mat i o n about radi ati on damage ,
but i t wa s fel t
that the h i gh temperatures and the smal l
in
actual
reactor
rad i ation effects.
operati ons
woul d
burnup
mi n i mi ze
The fuel el ement under tes t
i s made
in
ge n .
These tests provi de d , of course , no i nfor
The compo s i te fuel
is compared
from u n
a conti nuous phase of carb i de , as a web through
out the graphi te matri x .
The s tructu re of the
parti c l e s
2
embedded i n a conti nuous graphi te matri x . When
standard
fuel
shows
coated
uc
The
the carb i de coati ng l i ni ng the cool ant channel s
vol ume heat generati on produced by ohm i c heati ng
cracks i n th i s fue l , carbon i s l ost i ndefi n i tely
was
was
res i sti vel y
not
an
heated
wi th
accurate
de
curren t .
s i mul ati on
of
nucl ear
through the crack s because the graph i te matri x i s
heati ng , and changes i n fue l -el ement composi tion
conti nuou s .
duri ng the test affected the el ectri cal conduc
l ost through
ti v i ty o f the el ement potenti al l y cau s i ng prob
di spersi on phase i s exposed to the crack s , and
l ems.
then carbon stops escap i ng except for a
But
in
general ,
furnace
testi ng
was
val uabl e i n the devel opment o f new fue l -el ement
technol ogies and a 1 so i n qua 1 i ty-contro l sampl i ng
dur i ng manufacture of fuel
el ements for a spe
c i fi c reactor.
amount
W i th the compos i te fuel , carbon i s
coati ng
di ffu s i ng
cracks
through
unti l
the
the
carb i de .
c ar b i de
smal l
As
is
evi dent i n F i g . 3 2 , the compos i te fuel d i d i ndeed
p e rform better than the graphi te fuel .
Howeve r ,
for reasons that have n o t been ful l y determi ned ,
A maj or probl em al l uded to earl i e r through
the mi drange corrosi on
was
sti l l
greater
tha n
out the fuel devel opment program wa s the mi drange
expected .
c orros i o n , a s exemp l i fi e d i n Fi g . 32.
It was the
uted i n part to crack i ng from excessi ve thermal
re g i on about one-th i rd the l ength from the col d
s tre ss that re sul ted from a decrease in thermal
end of
conducti v i ty
the core where corro s i o n wa s
greatest .
Th i s unexpected corro s i on was attri b
duri ng
the
power
run.
Th i s
The i nl et end of the core had l ow corrosi on rates
decrease , which was measured, i s thought to have
becau se
been
the
temperatures
were
l ow.
The
fuel
cau sed
by
fi s s i o n
fragments .
Presumably
operated at much h i gher temperatur�s toward the
s uch an effect woul d not occur in the standard ,
nozzl e chamber end of the core , but the fuel wa s
coate d- parti cl e , matrix fuel because the fi s s i o n
proces sed duri ng fabri cati on to accept the h i gh
fragments do n o t penetrate through t h e part i c l e
end
coati ngs to damage the matri x .
temperature s .
Al so the neutron
hence the power densi ty , was l ow ,
l ow
thermal
crac k i n g .
ca rbon
stresses
There ,
a nd
fl ux ,
and
re sul ti ng i n
consequently
mi n i ma l
mass l oss wa s mo stly d u e to
di ffu s i o n
through
the
carbi de
coati ng .
Pure ( U , Zr ) C c a rb i de fuel s were al so tested
i n NF -1 as another approach to reduci ng corro
s i on .
The fuel el ements were fabri cated as smal l
hexagonal rods wi th one cool ant channel at the i r
Howeve r , i n the mi dra nge , the power densi ty was
center.
h i gh and the temperature wa s now apprec i abl e , yet
but it cracked exten s i vely as a resul t of i ts l ow
The fuel exper i e nced mi n i mal corro s i on ,
1 ow
s ti l l much l ower than that at whi ch the fuel wa s
fracture
processe d ;
ti v i ty .
However,
because of mi smatched expan s i o n coeffi c i ents, and
fracture
ch aracteri sti c s
hi gh mas s l osses woul d occur through the crack s .
rede s i gni ng thei r shape to reduce thei r cross
T h e i mproved performance of the ZrC coati ng
is
secti on and web th i ckness, the performance o f the
cl early shown i n Fi g . 3 2 , a s i s that of a new
carb i de el ements coul d be substanti al l y improve d .
type of fuel cal l ed composi te fuel .
Yet another advanced
the
carbi de
The composi te fuel
e nd
of
the
Rover
coati ngs
woul d
crack
was devel oped near th e
program
and
tested
in
Nucl ear Furnace al o ng wi th pure carb i de fuel
the
as
near
re si stance
the end
of
by
the
and
thermal
i ncreas i ng
fuel
of
the
the
conduc
strai n-to
el ements
was
bei ng
program.
Th i s
and
devel oped
fuel
wa s
s i mi l ar to the standard uc -coated part i c l es i n
2
graphi te-ma tri x fue l , but the graph i te matri x wa s
15
made wi th
matri x
POCO
hav i ng
carbon-fi l l er fl our to y i el d
a
h i gher coeff i c i ent
of
a
thermal
fuel s
NbC or ZrC channel coati n g s .
as
the
hi gh-CTE
Thi s fue l , referred
graphi te-matri x
fabricated i nto fuel
fuel ,
wa s
el eme n t s , and i t exh i b i ted
el ectri cal - p ower
the reactor devel opment.
early
K i wi
seri es
i nteractions.
adequate
But the
Reactor cores
es senti al l y
demonstrate d .
support
Improvements
system
in
system conti nued to be made ,
the program shou l d be seri ously consi dered i n any
s u111na ri zed i n Tabl e I .
future graph i te fuel -el ement devel opme n t .
that
demonstrated
operati ng
performance
of
what
termi nati o n of power.
test,
2400-2 600 K .
mai nl y
Thi s
in
the
performance
from the NRX -A6
and
demon s trated performances
range
was
Pewee
of
obta i ned
tests .
The
o f the advanced com
p os i te a nd pure carb i de fuel s were nearly
2 h
( 109 mi n ) at 24 50 K and at a peak power densi ty
3
i n the fuel of 4 500-5000 MW/m , as obtai ned i n
the N F - 1 tes t .
had
the
been
structural
wi th
the
resu l ts
It shoul d be emphasi zed
structural
the standard graphi te-matri x fuel w a s 1 h at a
temperature
from
anomal i e s
exi sted
were
determi ned after the tests and d i d not cau se a
cool ant
exi t
i n the
apart
By the end o f the K i wi seri e s , a n
s tructural
promi s i ng resul ts obta i ned before cancel l ati on o f
The
fel l
vi brati on s ; these were i nduced the rma l - hy drau l i c
standard fue l .
t h a t , u nfortunate l y , d i d n o t take pl ace .
appl i ca
Fuel structures were al so a maj or probl em i n
better s trai n-to- fai l ure charac teri sti cs than the
It was i ntended for the NF-2 tes t
production
tions.
expans i on ( CTE ) that cl osely matched that of the
to
for
some
crack i ng
At the end of the N RX-A6
in
the
beryl l i um- refl ector
ri n g , support bl ock s , peri phera l compos i te c u p s ,
a nd o n e tungsten cup wa s found .
These
were
of
bel i e ved
to
be
the
resul t
cracks
excess i ve
thermal gradi ents .
IV.
ENGINE DEVE LOPME NT
Based on the extensi ve fuel s work
ach i e ved duri ng the Ro ver program, proj ections of
endurance
l i mi ts
F i g . 34.
These
composite fuel
were
esti mated
proj ections
as
i nd i cate
shown
in
that
the
shoul d be good for 2-6 h i n the
temperature range of 2500- 2800 K .
Simi l ar per
A.
Engi ne Tests
An
engi ne
devel opment
program wa s c arri ed
out as part of the nucl ear reactor researc h and
devel opment
te st
seri e s
of
Phoebus
and
NRX.
Pri me responsi b i l i ty for th i s e ffort rested wi th
formance can be expected at 3000-3200 K for the
the
c arbide fuel s , a s sumi ng that the crack i ng probl em
objecti ve
can be reduced through i mproved desi g n .
extend nuc l ear rocket technol o gy i n preparati on
of operation,
l i mi ted
to
2200-2300 K ,
For 10 h
the graphi te-matri x fuel woul d be
a
cool ant
the
nearly 2 400 K ,
exi t
composi te
and
the
temperature
fuel
p u re
coul d
carb i de
go
to
Aeroj e t- General
of
thi s
Corporati o n .
test
for a fl i ght system.
seri e s
The
pri ma ry
to
further
was
Thi s i nvol ved i ncorporati ng
of
the advances made i n reactor devel opment i n to a n
to
engi ne that compri sed the nonnuc l ear components
about
of
a
compl ete
i nterest
3000 K .
And so the program was termi nated wi th three
s ta rtup ,
were
fl i ght
the
shutdow n ,
system .
Of
pa rti cul a r
i nvesti gati on
and
restart
of
e ng i ne
characteri sti c s
promi s i ng fuel forms at hand , the carbi de-carbon
for di fferent i n i ti a l condi ti ons; the eval uati ng
composi te ,
of
graph i te
the p u re carb i de ,
matri x .
As
and
di scu ssed
the
hi gh-CTE
above,
much
vari ous
control
performance
of
concep t s ;
and
testi ng
nonnucl ear engi ne components
the
in
testi ng wa s performed on these fuel s , but thei r
the nucl ear envi ronment.
corro s i on
test seri es c a n b e categori zed i n th i s program .
( 50 l
These are NRX/EST ,
w h i ch was carri ed out i n
5 1 52)
February-March 1 96 6 , and X E ' , ( •
wh i ch took
stood .
beha v i or
was
not
be
under
Mos t of the wo rk was done i n the tempe ra
ture range o f 2000-2800 K .
to
compl etely
extended
to
l ower
Th i s range woul d have
temperatures
( bel ow
pl ace
in
March
through
Two ful 1-power nuc l ea r
August 1 969.
Both
of
1 500 K ) and testi ng done wi th gases other tha n
these tests empl oyed 1 100-MW N RX -type reacto r s .
hy drogen
I n addi tion, a col d-fl ow test seri es Experi mental
16
to eval uate
the
performance
of
these
Engi ne
Col d
Fl ow
( XECF )
wa s
conducted
in
Febru a ry-Apri l 1968 .
The N RX/EST
di spl ayed
in
Fi g . 35
was
the
fi rst operati o n o f a N ERVA breadboard power p l ant
wi th
eng i ne components
func ti onal
s hutoff val ve i s fi rst opene d , the pump tends to
vapori ze the fl u i d u nti l s uffi c i ent fl u i d p a s se s
connected
rel ati onshi p .
The
in
a
fl i ght
te st demon s trated
th rough i t t o c h i l l
condi tions.
poi nt,
as
are
Therefore ,
down t h e pump t o cry ogenic
The nozzl e al so tends to be a choke
the
core
a certa i n
and
refl ector
amount
of
fl u i d
i nl ets .
mu s t b e
the s tab i l i ty of the power p l ant u nder a number
pa s sed through t h e system to remove t h e stored
of di fferent control modes wh i l e the e ngi ne oper
heat i n the l i ne s , val ve s , and refl ecto r .
ated over a broad area o f i ts performance map .
th i s i s accomp l i shed , the pump can be started and
Once
The endurance capabi l i ty of the reactor and other
wi l l
engi ne components was demonstrated by operati ng
fl u i d fl ow i s nece s sary t o accomp l i sh th i s func
the power p l ant at s i gni ficant power duri ng
ti o n .
5
operate normal l y .
Approximately
1
mi n o f
Duri ng thi s time peri o d , the reactor can
d i fferent days for a total of 1 h and 50 mi n , of
be b rought
whi ch
tests
drums are prograR111e d out rap i dl y , a l mo s t to the
served to demo nstrate the mul ti p l e restart capa
col d cri tical poi nt, and then put on a sl ow tran-
bi l i ti e s o f the engi ne , i nc l udi ng the fea si bi l i ty
s i ent .
of
sensed
28 mi n were
restart i ng
the
at ful l
power .
eng i ne
These
wi thout
an
external
Operati on of the XE '
E ng i ne
( Fi g s . 36 and
Thi s
to
Once
in
swi tched
power sourc e .
up
l ow-power
to
chamber ,
the
c l o sed-l oop
does
not
l evel .
Reactor
temperature
apprec i abl e
the
scheme
a
reactor
is
can
be
contro 1 .
temperature
requi re
ri s e
any
neutron i c
3 7 ) wa s the fi rst te st o f a down-fi ri ng nucl ear
i ns trumentati o n .
rocket e ngi ne wi th components in a fl i ght- type ,
achi eved and the turbopump i s run n i ng , the e ng i ne
cl o s e-coupl ed arrangement.
can
The te st stand p ro
be
When apprec i abl e power h a s bee n
accel erated
at
the
rate
of
83 K / s .
( a bout
Ex peri ence on the NRX/EST a n d XE ' engi ne programs
1 p s i a , o r 60 000 ft al ti tude) around the eng i n e
s howed that the engi n e system can be control l ed
to
i n a predictabl e and safe manner.
v i ded
a
reduced
parti a l l y
atmosph eri c
s i mul ate
sp ace
pre s sure
condi tions.
e ng i ne was successful l y operated at ful l
The
power .
I t r a n at vari ous power l evel s o n di fferent days
for a total
of 1 1 5 m i n of power operation that
i ncl uded
resta rt s .
28
The
bootstrap
startup s
B.
E ngi ne Design Improvements
(SS)
Other goal s of the eng i ne devel opment pro
gram,
bes i de s
demo n s trati ng
e ngi ne
fea s i b i l i ty
( w i thout external power) were accomp l i shed over a
and control , were fi rst of al l to max imi ze spe
range of pump
c i fi c
i n l et sucti on pressu re s and wi th
impul se ,
whi ch
is
proporti onal
to
th e
reactor cond i t i o n s sp anni ng the range that woul d
s quare root of the nozzl e chamber temperature ; to
be encountered i n fl i ght operat i o n s .
Compl etel y
meet vari o u s des i gn thrust l evel s that a re pro
a utomatic
The
startup wa s
demonstrate d .
capa
port i onal to fl ow rate and that demonstrate the
b i l i ty of the engi ne to fol l ow demanded tempera
capabi l i ty
ture ramp rates up to 56 K/ s was demon strated ,
operate at a reduced th rust; to mi n i mi ze e ng i ne
and
ba sed
on
thi s
i nformati on ,
a s surance
wa s
to
throttl e
the
e ngi n e
down
and
s i ze and we i ght; and to i ncrease l ongev i ty from
gai ned that rates up to 83 K / s coul d be achi eved
an i n i ti al
wi thout exposi ng any of the e ngi ne components to
ati ng l i fe i s real l y determi ned by the amount o f
a
transi ent
condi tion
that
woul d
exceed
i ts
des i gn l i mi tati o n s .
1 h to 10 h .
In fac t , system oper
propel l ant that c a n be tran sported t o sp ace i n a
reasonabl e payl oad to perform the mi s s i o n .
F i gure 3 8 shows some of the characteri s t i c s
52-54 l
The
made fi rst of a 1 1 by i mprovi ng the reactor fuel
e ng i ne components must be condi ti oned before hi gh
p e rformance to permi t ra i si ng the operati ng tem
p ower can
be
p erature , as di scussed i n the precedi ng ch apter.
refl ecto r ,
and core i nl et a re al l
o f sta rti ng an eng i ne of th i s sort . (
ope.rate
at
reached .
l ow
The
temperature s .
turbopump ,
nozzl e ,
desi gned
When
the
I nc reases
in
the chamber
to
A number o f des i gn changes
pump
i mprove reactor perf ormance .
temperature were
al s o were made
to
The cores of the
17
early reactors were
ti e
engi ne ( 56 • 5 7 )
The
esti mate s are detai l ed i n Tabl e I I I .
supported axi al l y wi th
rods attached to the col d-end support p l ate .
rods were cool ed by hy drogen that di scharged i nto
a nd Phoebus-2A were tested .
Ma s s
A compari
son of j u st the reactor ma sses was shown earl i e r
the nozzl e chamber, and th i s cool i ng 1 owe red the
in
rocket speci f i c i mpul se because the ti e-rod cool
desi g n s
Fi g . 1 0 .
Both
the
NERVA
and
Smal l
E ng i ne
ant exi t temperature was much 1 ower than that o f
i dea.
advantage of the ful l - fl ow cyc l e
1 58-6 1 )
The NERVA
was desi gned for the
the cool ant exi t i ng the ma i n fuel e l ements.
3 37-kN
( 7 5 000- l b )
In
l ater reactors and i n engi ne sy stems desi gned for
took
thrust l evel
reactor, and the Smal l E ngi ne was desi gned for a
fl i gh t , ti e tubes were substi tuted for tie rods .
7 2-kN thru st l evel
T h e tube s were
equi val ent vacuum spec i fi c
regenerati vely
c oo l ant di scharg i ng i nto
than the core ex i t .
chamber.
was
Thi s
fl ow rate wa s u sed to
temperature .
i nterfac e ,
di scharged
fl ow was
a l most noth i ng
to
the
the core i n l et rather
protect the core-refl ector
f l ow
wi th
Al s o , in the earl y reacto r s ,
a l arge core peri pheral
c oo l er
cool ed
steadi l y
i ncrease
A fi nal
i nto
the
and
the
e ngi ne wa s 7 10 s .
wi th a 367-MW reactor.
E ng i ne .
The
i ncrea s i ng spec i f i c
are refl ecti ons of the chamber temperatures that
went from 2 2 70 K as demonstrated i n the XE ' tes t
to
chamber
to
to a des i gn val ue o f 2 6 9 5 K for the Sma l l Eng i n e .
3l
The
Smal l
Engine( 2 •
dep i c ted
s chemati cal l y in Fi g . 39 real l y re presents a n accumu1 ati o n of al l
n ucl ear rocket program .
T h e engi ne fl o w cycl e w a s al so changed t o
The XE
impul se l evel s
thi s
opti mi zati on woul d be
impul s e .
The
the X E '
Thi s was i mproved to 825 s for
the p eri phery a s semb l y .
sp ec i fi c
of
the NERVA fl i ght e ng i ne and 875 s for the Smal l
emp l oy a regenerati vely cool ed heat exchanger for
i ncrease
i mpul s e
nozzl e
decreased
nozzl e
u s i ng a 1 570-MW
eng i ne
em
propel l an t ,
and
a
of the k nowl edge
gai ned
in
the
It u sed hy drogen as the
the ful l -fl ow engi ne topp i ng cycl e ,
s i ngl e- stage
centri fugal
p ump
wi th
p l oyed the " h o t-bl eed" cycl e to dri ve the cool ant
si ngl e-stage
turbopum p .
cool ed nozzl e and ti e-tube s upport el ements .
I n th i s cycl e ,
some cool ant is ex
tracted from the chamber and mi xed wi th cool a n t
turb i n e .
I t had
a
a
regenerati vel y
A
radi ation s h i e l d of borated z i rconi um hy dri de wa s
from the re fl ector outl et , and tne combi ned cool
i ncorporated above the reactor.
ant i s u sed to dri ve the tu rb i n e .
t o reduce heati ng to the propel l a nt tank above
turb i ne exhaust
coul d not be
stream;
pre s sure
rei n troduced
is
l ow,
i nto
Because the
th i s
cool ant
the mai n
fl ow
i t was di scharged i nto space at a 1 ow
Thi s was ma i nl y
the engi ne , al though it al so provi ded s h i el di ng
for the payl oad and crew.
Reactor control wa s
done wi th s i x actuators for the 1 2 control drums
temperature rel ati ve to the nozz l e chamber cond i
i n the beryl l i um refl ector.
tions,
o n l y fi ve val ves and the i r ac tuators, i ncl udi ng a
thereby
reduc i ng
the
overal l
spec i fi c
impul se of the e ng i n e .
Fi nal
eng i ne
The e ngi n e empl oyed
propel l ant tank shutoff val ve ( PSOV ) 1 ocated a t
de si gns
evol ved t o empl oy
a
the bottom of the propel l ant tank t o provi de a
ful l -fl ow or top p i ng cycl e i n whi c h the turbi n e
ti ght seal
recei ves fl u i d from the tie- tube outl et a n d di s
e ng i ne
charges
cyc l e ,
( NC V ) to adj u s t the fl ow spl i t between the nozzl e
never tested experi mental l y , s i g n i f i cantly ra i se s
c ool ant tubes and the t i e tube s ; a turb i ne seri e s
t h e spec i f i c i mpul se of the e ngi n e .
control
val ve
i nl et temperature i n the ful l - fl ow cycl e i s much
i sol ate
the
l ower than i n the hot-bl eed cycl e .
cool down to remo ve after-heat and to extend the
much
i t i nto
the
greater turb i ne
core
i nl et.
f l ow rates
Thi s
The turb i n e
Consequentl y
and
di scharg e
pressures a re requi red than i n the former cycl e .
is
c ontrol
( T BC V )
agai n s t propel l ant l eakage whe n the
not i n u s e ;
( TSC V )
turbi ne
range;
a
a
nozzl e control
that
coul d
duri ng
turb i ne
N E RVA a n d Sma l l E ngi n e Designs
Des i g n characte r i s ti c s for
rate ;
byp a s s
severa l
e ngi nes
are l i sted i n Tabl e I I . Only the experimental XE '
18
control
to regul ate the amount of
and
re gul ate
a
cool down
hydrogen
fl ow
control
for
used
preconditioni ng
turbi ne and th u s the turbopump
C.
be
val ve
speed and
decay
fol l owi ng engi ne operati on and
heat
and
val ve
fl ow to
val ve
to
( CC V )
the
f l ow
to
removal
together wi th a
smal l pump , to provi de prepressuri zati o n for the
fl at.
tan k .
the overa l l reactor d i ameter wa s 950 mm.
As
A regenerati vely cool ed nozzl e was u sed out
to the area rat i o of 25 : 1 .
u ncool ed
sk i rt
secti o n .
I t was fol l owed by an
Thi s
secti on
extended
the nozzl e out to an area rati o of 100 : 1 .
The
The effective core d i ameter was 570 mm and
shown
Engi ne
wei ght
( m i nus
the
F i g u re 4 2
in
Tab l e I I I ,
was
the
2550 kg ,
shi el d)
w i th
a l most
s u11111a ri zes
the
Smal l
u nc oo l ed nozzl e s k i rt wa s h i nged to faci l i tate
poi nts at des i gn cond i ti on s .
pera tu re was nearly 2 700 K .
The overal l e ngi ne 1 ength
reactor
of
thi s .
E ngi ne
state
The chamber tem
wou l d mate wi th the propel l ant tank so a s to f i t
was 3 . 1 m wi th the s k i rt fo l ded, or 4 . 4 m w i th
w i th i n the space s huttl e .
the ski rt i n p l ac e .
mari zed i n F i g . 43 .
The total mas s of the system
Smal l
A s tudy was made to see how the Smal l Engi ne
ment. provi ded room for a 1 arger propel 1 ant tank
i n the 1 aunch vehi c l e .
the
1 600 kg
packagi ng i n the 1 aunch veh i cl e .
Th i s arrange
overal l
T h e re sul ts are sum
The nucl ear stage w i th the
Smal l E ng i ne woul d we i gh c l ose to 18 000 kg , of
was 2 550 kg .
The reactor core , p i c tured i n Fi g . 40 , wa s
wh i ch a l most 13 000 kg woul d be propel l an t .
If
desi gned to produce about 370 MW .
There were
t
�64 hexagona l ly shaped , ( UC -Z rC ) C composi te fuel
a dd i tional propel l ant modul es were sent u p sepa
el ements contai ni ng a total o f 52 . 4 kg o f urani um
wi th over 2 1 000 kg
( 0 . 93 1 5 enri chment) .
propul s i on .
coo l ant chan nel s .
Each fuel
el ement had 1 9
There were 241
suppo rt el e
ratel y ,
the stage woul d then wei gh
nuc l ea r
of
hydrogen
23 000 kg ,
avai l abl e
s tage
wou l d
operate
for
approxi mately
ments , conta i n i ng z i rc o n i um hydri de , ZrH , a s a
2
neutro n moderator .
The core peri phery i ncl uded
woul d add 2500 s to the operati ng time .
an outer i nsul ator l ayer, a coo l ed i nboa rd s l a t
pos s i b l e l i fetime of several
secti o n , a metal wrapper, a cool ed outboard sl at
performi ng many s i g n i ficant mi s s i o n s .
secti o n , and a n expan s i o n gap .
1 500 s i n space . An addi ti onal propel l ant modul e
The co re was sup
po rted on the col d end by an al uminum al l oy p l ate
D.
Component Devel opment
w i th the support p l ate resti ng on the refl ector
system .
The reactor was contai ned i n an al umi num
press u re
vesse l .
reacti v i ty
A
control
bery l l i um
drums
bar.rel
surrounded
wi th
the
12
core .
for
At a fl ow rate of 8 . 5 kg/ s , a s i ngl e
Th u s , a
hours woul d al l ow
( 60 l
A vi gorous program for the devel opment of
nonnucl ear
eng i ne
components
accompani ed
reactor and engi ne test programs.
the
The pri nc i pal
components were the mai n cool ant turbopump , the
The reactor was desi gned for 83 K/ s temperature
val ves and actuators,
tra n s i ent s .
reactor pre s s u re vessel , radi ati on s h i el di n g , and
F i gure 4 1 provi des more detai l s o n the fuel
modul e s .
The
fuel
provi ded
the
heat
It
consi sted o f a
sol i d
sol uti on
composi te
and carbon.
matrix
The
of
channel s
UC -ZrC
were
the
the contro l s and i ns trumentati o n .
tran sfer
s urface and the energy for heati ng the hydrogen.
the nozzl e a s sembly ,
F i gu re 4 4
is
a
p i c tu re
of
the
turbopump
devel oped for the XE ' eng i ne , i nc l udi ng a l i sti ng
of some key parameters rel ated to the turbopump .
The pump performs
the
functi on of p ressuri z i ng
coated wi th z i rconi um carb i de to protect aga i n s t
the propel l ant for the engi ne feed system .
ti;' drogen
1 ow f l ow rates requi red by the Smal l E ng i ne made
reacti o n s .
The
ti e
tubes
transmi tted
the core axi al pres s u re l oad from the hot end o f
it pos s i b l e to run
the fuel
h i gher rate than for the XE '
e l ements
to the
core
support
pl ate .
The
the shaft speed at a much
eng i ne or NERVA .
They al s o provi ded an energy sou rce for the turbo
The X E ' turbopump was a s i ngl e-stage , rad i al exi t
pump
fl ow,
and
conta i ned
and
cool ed
carbide moderator sl eev e s .
the
z i rc on i um
They consi sted of a
counterfl ow heat exchanger of I nconel 7 1 8 and a
z i rconi um
c ar b i de
hydri de
i nsul ation
moderator
sl eeves .
0 . 89 m l ong and meas u red
wi th
The
z i rconi um
el ements were
1 9 . 1 mm from fl at
to
centri fugal
pel l e r ,
a
power
pump
wi th
transmi s s i on
an
al umi num
that
coup l ed
pro
the
pump to the turbi ne , a nd a two- s tage turb i ne wi th
stai nl e s s steel
roto r s .
On N RX/EST ,
th i s pump
perf ormed e i ght start s and operated 54 . 4 mi n at
h i gh
power.
In
the
XE '
eng i n e ,
it
performed
19
28 sta rts and restart s , i ncl udi ng runs to rated
power.
Poten tial
probl em areas were
wi th
the
shaft system bi ndi ng at the beari ng cool a n t ,
a
s tai nl e s s steel
for the cool ant channel s .
The
graphi te nozzl e extens i on wa s u ncool ed out to an
a rea
ratio of 100 : 1 .
The cool ed section
u sed
di ffi cul ty that was experi enced i n the XE tes t s .
U- tube
The
The maj o r unresol ved probl ems in ach i evi ng a 10-h
sol u ti on w a s t o i ncrease c l e arance a n d to
improve al i gnment.
the
few
nucl ear
Beari ngs are probabl y one of
l i fe- l i mi ti ng
subsystem.
components
in
Resul ts o f l i fe
l i sted i n Tabl e I V .
the
non-
tes ts
a re
The sol uti o n to the beari ng
constructi ons
and
a
di vergent
s ection.
l i fe we re a ssoc i ated wi th some remai ni ng s tress
probl ems
in
the
al umi num
al l oy .
Fabrication
probl ems appear to have been resol ved .
probl em seemed to depend on mai ntai ni ng adequate
F i gure 48
(64)
encl osure .
cool i ng to reduce wear.
the components of the reactor a s sembl y , to form a
to
Vari ous val ves were requi red in the system
( 5 2 • 60- 6 2 )
the hy drogen fl ow.
These
control
dep i cts
Its
pressure shel l
the
pre s sure
f u nctions
were
ves sel
to
and
support
for the hy drogen prope l l an t , and
to tran sm i t thrust to the thrust s tructure .
The
val ves were b i na ry va l ve s , except for the i n-out
desi gn cond i ti o n s ,
control val ves and check val ves , such a s s hown i n
were a maxi mum fl ow rate of 3 7 . 6 kg/ s ,
Fig. 45.
pressure of 8 . 6 6 MPa , temperature ra nge from 20
Val ve
operati ng
experienc e
wi th
a
reactor was obtai ned i n both the NRX/EST and X E '
to
eng i ne
fa i l u re s i n 10
test s .
actuato r
Tabl e V
l i sts
characteri sti c s .
the
T he
val ve
maj o r
and
potenti al
180 K ,
10 h.
as
speci f i ed for the N ERVA ,
maxi mum
rel i abi l i ty of fewer than three
6
fl i gh t s , and a serv i c e l i fe of
Simi l a r desi gns were demonstrated i n the
probl ems appeared to be from seal damage by con
fi ve NRX tests a nd the X E ' eng i n e .
tami nants,
v e s sel wa s constructed of a cyl i nder that had a
erroneous
posi ti on
i ndicator s ,
and
top cl o su re wi th bol ts and seal s .
l eakage from poor l i p-seal tol eranc e s .
T h e number of val ves i n the Smal l Engi ne was
fi v e .
However,
there wa s
some
The pre s su re
des i re
in
the
A one- p i ec e
extruded forg i ng of al umi num al l oy 707 5-773 w a s
u sed ,
wi th
a
su rface
coati ng
of
Al o •
The
2 3
bei ng de si gned we re the best
NERVA fl i ght e ngi ne to i ncrease system rel i abi l
maj or i terns sti l l
i ty by h avi ng
two turbopumps ,
e i ther of wh i ch
ways of as suri ng bul k prel oad and of f i nal i zi ng
coul d
ful l
pre s s u re
the su rface coati ng s .
provi de
f l ow
the
ti on s .
I n o rder to provi de swi tchi ng between the
and
to
redundant val ve
to
systems,
turbopumps
a nd
and
e ng i ne
pro v i de
h i gh
confi gura
rel i abi l i ty
by
A radi ati on shi e l d was l ocated between the
The shi el d
reactor co re and the propel l ant tan k .
was i ntended to prevent neutron heati ng of the
back i ng up each val ve i n case o f a fai l ure , some
propel l an t ,
26
val ves
woul d
be
needed ,
as
seen
in
(6l)
I ndeed i t becomes que sti onabl e
F i g . 46.
s h i e l d i ng for the crew as the tank empti ed o f i ts
and
it
propel l ant.
whether the redundancy gai ned i s worth the added
des i gn prob l em s .
It did
(65)
al so
prov i ded
not present
any
The nozzl e assembly i s u sed to expand the
a rea
of
! 3 5l
devel opment
duri ng
the
heated gas from the reactor i n order to pro vi de
gram .
max i mum
mati c- type actuators were devel oped .
NERVA
thrust.
(63)
The
fl i ght
A
nozzl e
des i gn
e ngi ne
were
is
p i ctured
cond i ti ons
a
thrust
in
For
the
demonstrated on the XE '
l evel
of
degradati on or anomal i e s .
I n strumentati o n wa s
ment .
chamber
di spl aceme n t ,
and
of
cool ant
between 28 and 33 K .
2360 K ,
f l ow
channel
rate
of
temperature
The regenerati vely coo 1 e d
nozzl e part used an al umi num al l oy j acket and
20
Rover
actuators,
pro
pneu
These were
e ng i ne wi thout apparent
al s o a
maj or devel op
Thermocoup 1 es demon strated pe rformance at
10 h, rel i abi l i ty of fewer than four fai l ures i n
4
10
fl i ghts,
chamber
pre s sure
of
3 . 1 MPa ,
temperature
control - drum
for
337 kN , an area rati o of 100 : 1 , a servi ce l i fe of
4 1 . 6 kg/ s ,
d i ffi cul t
Co ntro l s a n d i n struments were another major
system comp l exi ty .
Fig. 47.
b i o l ogical
2 667 K for 1 h wi thout degradati on.
p ressure ,
and
Thermocoup l e
v i brat i o n
sensors
were devel oped for several hours of operati on.
A
1% measurement accuracy wi l l requi re some f u rther
devel opme n t .
Control l og i c reached a h i gh degree of auto
mati on wi th
demo n s trati o n
o f automati c
control
systems i n X E ' for al l operati onal phase s .
Feed
experi mental
spec i f i c
eng i ne , but the h i ghe s t equ i val ent
i mpul se
achi eved was 845 s
in
Pewe e ,
which operated at a peak cool ant exi t temperature
back control l oops and drum posi ti o n , power , tem
of 2550 K and a peak fuel temperature of 2750 K .
perature ,
A
turb i ne
control
val ve
pos i ti o n ,
and
p re s s u re were devel oped .
Testing fac i l i ti e s were another maj or devel
opment i tem .
average power densi ty a s h i gh as
3
2340 MW/m and peak maxi mum fuel power den s i ty
3
of 5200 MW/m were obtai ned as wel l i n Pewe e .
The N F - 1 , which experi enced nearly as h f gh peak
Testi ng Faci l i ti e s
E.
core
Duri ng the nucl ear rocket pro gram ,
p ower dens i ti e s , ran at ful l power a nd a n average
cool a nt exi t temperature of 2445 K for an accumu-
maj or test faci l i ties were devel oped at the NRDS
1 ated
at Jacka s s Fl ats
from
i n Nevada
( Re f . 2 ,
These
i nc l uded
reactor
test
test
fac i l i ti e s ,
and
as sembly
fac i l i ti es
( shown
earl i er
Vo l . I I I ) .
fac i l i ti e s ,
and
in
engi ne
di s a ssembl y
Fi g . 4 ) .
time
of
these
109 mi n.
tests
The
i ndi cate s
experi ence
that
the
gai ned
compos i te
fuel woul d 1 a s t for 6 h under these condf ti ons
t 49 l
before apprec i abl e fuel l os s occu r s .
The
The
nonnucl ear
components
of
the
e ng i ne
reactor test fac i l i ti e s were de s i g ned to te st the
proved to be capabl e of achi evi ng the endurance
reactor i n an upward- fi ri ng posi tion.
requi red
faci l i ty-type
feed
systems
for
The se u sed
prov i d i ng
the
and
for
bootstrap
testi ng .
Ful l y
automatic
control
startup were demonstrated
for
a
hy drogen to cool the reactor and to support the
w i de range of operati ng condi tions i n NRX/EST a nd
reactor tes t s .
XE ' , the l atter experi enci ng 28 eng i ne starts and
The fi rst downwa rd-fi ri ng faci l
i ty , which al so i nc l uded some atmosphere s i mul a
restart s
ti o n ,
56 K/ s , which cou l d be rai sed w i th confidence to
wa s
the eng i ne te s t faci l i ty .
Thi s
wa s
u sed i n the XE col d- fl ow te sts and al so the XE '
temperature
ramp
rates
up
to
83 Kl s .
ful l - power test .
Thi s sec t i o n descri be s the Rover technol ogy
For mai ntenance ,
as sembl i ng ,
and di sassem
bl i ng of the reactor and eng i ne system s ,
were
wi th
there
bui l di ng s cal l ed Ma i ntenance As sembly
and
base.
The program was termi nated at the poi nt of
fl i ght e ng i ne devel opment.
it
wou l d
Di sas sembly ( Ml\D ) , whi c h provi ded the necessary
reactor
fac i l i ti e s ,
testi ng ,
hot cel l s ,
and other equi pment for
be
and
and
necessary
e ngi ne
For a fl i ght system ,
to
veri fy
desi g n ,
veri fy
the
p e rfo rm
fl i ght
durati o n
There
reproduci bi l i ty .
putti ng together and tak i ng apart the reacto r s .
appear to be
The
c on structi on of a successful nucl ear rocke t .
MAD b u i l d i n g s were l i nked ( Fi g . 4 9 ) to the i r
no technol ogical
barri ers to
the
respecti ve test faci l i ti es by ra i l roads that were
u sed to transport the reactors by remote control
i f neces sa ry .
B.
Space Power Generation
The nucl ear rocket e ngi ne technol ogy base i s
d i rectly appl i cabl e to the generation of e l ectr i c
V.
FUTURE DEVELOPMENTS
A.
Fl i ght E ngi n e
power i n spac e , parti cul arly f o r hi gh-power ( so
c al l ed
systems.
The b a s i c research and technol ogy devel op
mul timegawatt ,
10- 1 00 MW ) ,
open-cycl e
(66)
A schemati c drawi g of s uch a
�
p ower pl ant i s shown i n F i g . 50 .
The pl ant i s
ment requi red for a nucl ear rocket fl i ght e ngi ne
s i mi l ar to a rocket e ng i ne i n whi ch the e ng i ne
were e ssenti al l y compl eted duri ng the Rover pro
nozzl e has been repl aced by a turbi ne to ge nerate
gram .
el ectri c i ty .
Power l evel s i n the range of 500-4100 MW
were demonstrated i n the NRX , Phoeb u s , and Pewee
test seri e s .
1 bl
A thru st l evel of 930 kN ( 200 000
was reached
i n Phoebus-2A with a
fl ow rate of 1 20 kg/ s .
A
7 10 s
obtai ned
( 6060 m/s )
was
speci fic
in
hydrogen
impul se
the
The cool ant gas i s then exhau sted
i n such a way as not to produc e any thrust.
core exi t temperatu re
of
the
hy drogen
The
cool ant
wou l d have to be much l ower than that of the
of
rocket engi ne because of materi al
XE
t h e turboa l ternator.
l i m i tations o n
Thi s mea ns t h a t f o r a gi ven
21
