solid core rockets

8/14/2019 solid core rockets

1/9

IEEE TRANSACTIONS ON NUCLEAR SCIENCE

REVIEW OF S O L I D CORE NUCLEAR ROCKETSFrancis C . S c h w e n k , ChiefAdvanced Engines BranchSpace Nuclear Propulsion OfficeU . S . Atomic E n e r g y CommissionWashington, D . C . 2 0 5 4 5

Summary This paper describes briefly th e programsunderway t o develop solid-core reactor t e c h n o l o g yf o r nuclear r o c k e t s . Recent successful KIWI a n dNERVA r e a c t o r s h av e s h o w n g r e a t p r o g r e s s i n t h edevelopment o f g r a p h i t e reactor t e c h n o l o g y a n dp r o v i d e a s o u n d basis f o r t h e ultimate develop-m e n t o f nuclear r o c k e t e n g i n e s f o r a variety o fs p a c e missions. In addition t o t h e reactor w o r k ,t h i s d i s c u s s i o n p r e s e n t s t h e e f f o r t s i n t h eNuclear R o c k e t Program f o r development o f non-r e a c t o r c o m p o n e n t s , s y s t e m s s t u d i e s a n d r e s e a r c h ,a n d f u l l n u c l e a r r o c k e t e n g i n e s y s t e m s t e s t s ( t ob e c o n d u c t e d i n t h e next 2 o r 3 y e a r s ) t o p r o v i d et he o v e r a ll t e c h n o l o g y required f o r applicationo f solid-core nuclear r o c k e t e n g i n e s t o m i s s i o n s .S o l i d core nuclear rocket engines are t h enext major advance i n propulsion t e c h n o l o g y f o ruse i n a c c o m p l i s h i n g d i f f i c u l t missions i n s p a c e .Recent results i n t h e Nuclear R o c k e t Program s h o wt h a t s o l i d c o r e reactors c a n b e developed t op r o v i d e a n uc le ar r oc ke t e n g i n e h a v i n g a h i g hs p e c i f i c i m p u l s e ( o v e r 7 0 0 s e c o n d s ) with a n a p -p r o p r i a t e t h r u s t t o w e i g h t r a t i o a n d t h a t anuclear r o c k e t e n g i n e c a n b e m a d e available f o rmissions t o b e accomplished i n t h e 1 9 7 0 s a n d1 9 8 0 s .T he c ur r e nt program i n o u r c o u n t r y f o r t h edevelopment o f nuclear rocket engines i s i n at e c h n o l o g y p h a s e . T h a t i s , w e a r e conductinga program t h a t includes a l l n e c e s s a r y componentsa n d t e c h n o l o g i e s f o r t h e nuclear r o c k e t e n g i n e t op r o v i d e t h e b a s i c i n f o r m a t i o n , d e s i g n d a t a , a n dpractical e x p e r i e n c e , s o t h a t , w h e n missionsr e q u i r i n g nuclear r o c k e t s are s p e c i f i e d , t h e f u l ldevelopment o f f l i g h t s y s t e m s c a n b e institutedwith a minimum d e l a y .T h e m a j o r effort f o r t h e d e v e l o p m e n t o f s o l i dcore reactor t e c h n o l o g y r e s t s o n graphite a s t h ef u e l m a t e r i a l . T h e n a m e s K I W I , N E R V A , a n dPHOEBUS refer t o t h e p r o g r a m s o r p r o j e c t s con-ducted o n g r a p h i t e s y s t e m s . I n a d d i t i o n , we a r es u p p o r t i n g research a n d d e v e l o p m e n t e f f o r t s t oe x p l o r e t h e f e a s i b i l i t y o f t u n g s t e n a s a materialf o r s o l i d c o r e nuclear r o c k e t s . T h i s articlewill describe t h e g r a p h i t e work f i r s t i n s o m edetail a n d t h e n mention b r i e f l y s o m e o f t h eactivities b e i n g conducted o n t u n g s t e n r e a c t o r s .F i g u r e 1 s h o w s a mockup o f t h e NERVA e n g i n ewhich a s b e e n under development s i n c e 1 9 6 1 a t t h eA e r o j e t - G e n e r a l Corporation ( A G C ) with Westing-h o u s e Astronuclear Laboratory ( W A N L ) a s t h ep r i n c i p a l subcontractor f o r n u c l e a r reactort e c h n o l o g y . Th e engine s t a n d s 2 2 f e e t high fromt h e t o p o f t h e f l a n g e which m a t e s t o t h e h y d r o g e n

propellant t a n k i n t h e r o c k e t v e h i c l e t o t h ee x h a u s t e xit o f t h e j e t n o z z l e . T h e r e a ct o rwhich i s b a s e d o n t h e K I W I design developed a tt h e AE C Los Alamos Scientific Laboratory ( L A S L )i s l o c a t e d within t h e pressure vessel within t h ecentral portion o f t h e engine. T h e l a r g e s p h e r e scontain hydrogen g a s under pressure t o providef o r actuation during engine start-up p e r i o d s .T h e nozzle c o n s i s t s o f a convergent-divergentsection c o o l e d b y t h e main p r o p e l l a n t f lo w a n da n additional divergent s k i r t which increasest h e nozzle e xp an si on r a ti o t o whatever m a y b ed e s i r e d .Figure 2 s h o w s a drawing o f a nuclear r o c k e to n wh ich t h e p r o p e l l a n t f lo w p a t h c a n b e t r a c e d .During operation, l i q u i d hydrogen f l o w s f r o m t h et a n k t h r o u g h t h e t a n k s h u t o f f v a l v e i n t o t h epump suction l i n e which contains a gimble b e a r -i n g f o r thrust-vector a d j u s t m e n t . A centrifugal-f l o w p um p p re ss ur iz es t h e p r o p e l l a n t ; t h e pro-p e l l a n t t h e n enters t h e pump d i s c h a r g e l i n e andf l o w s t o t h e nozzle inlet m a n i f o l d . T h e mainpropellant f l o w passes through t h e nozzle coolingpassages removing heat transferred t o t h e nozzlef r o m t h e main e xh au st s tr ea m a s well a s heatgenerated i n t h e nozzle pressure vessel b ydeposition o f n uc le ar r ad ia ti on ( n e u t r o n andg a m m a ) e n e r g y .

T h e coolant l e a v e s t he nozzle a s a l o w -t e m p e r a t u r e , l o w - d e n s i t y f l u i d a n d d i v i d e s intop a r a l l e l f l o w s t o c o o l t h e p r e s s u r e v e s s e l , t h er e f l e c t o r , a n d t h e c o n t r o l d r u m s . T h e propellante x i t s from t h e reflector region a n d i s directedalong t h e pressure vessel dome t o removeradiation d e p o s i t e d t h e r e . Th e h y d r o g e n flowt h e n cools t h e shield and enters t h e reactorp l e n u m .Th e p r o p e l l a n t i s distributed from t h e inletplenum into s e v e r a l p a r a l l e l p a t h s . T h e b u l k o ft h e flow enters t h e reactor f u e l element coolingp a s s a g e and i s heated t o h i g h t e m p e r a t u r e s . Th e

r e m a i n i n g p r o p e l l a n t i s distributed t o flowp a s s a g e s which cool various reactor structuralcomponents and t o t h e p e r i p h e r a l r e g i o n betweenthe hot reactor core and t h e r e f l e c t o r . Th evarious coolant f l o w s merge at th e r ea ct or e xitplenum which i s also t h e nozzle in t h e c h a m b e r .I t i s e v i d e n t , t h e r e f o r e , t h a t t h e a v e r a g etemperature o f t h e g a s results f r o m a mixture o ft h e ho t g a s e s l e a v i n g t h e f u e l element f l o wc h a n n e l s and the cool g a s e s e x i t i n g from th estructural coolant p a s s a g e s .Th e p r o p e l l a n t i s then e x p a n d e d t h r o u g h t h enozzle t o exhaust v e l o c it i e s g r e a t e r than 2 3 , 0 0 0

1 6 0 F e b r u a r y


2/9

SCHWENK: SOLID CORE NUCLE R R O C K E T Sf e e t p e r s e c o n d , c o r r e s p o n d i n g t o a s p e c i f i cimpulse greater than 700 s e c o n d s which i s t y p i c a lo f s o l i d core nuclear rockets.

T h e turbine drive f l o w i s obtained b y e x-tracting g a s f r o m t h e nozzle chamber t h r o u g h ap o r t i n t h e wall of the nozzle. The hot gas fromt h e r ea ct or e xi t m u s t b e diluted i m m e d i a t e l y withc o l d g a s t o produce t h e d es ir ed t ur b in e -i nl e ttemperature. Gas t h e n f l o w s t h r o u g h th e turbineinlet l i n e p a s s i n g t h r o u g h the turbine p o w e rcontrol valve that r e g u l a t e s turbine flow a n d ,t h e r e f o r e , t h e turbine power and pump s p e e d . Th ef l o w i s e x p a n d e d t h r o u g h t h e turbine w h i c hextracts t h e p o w e r r e q u i r e d t o maintain theturbopump s p e e d a n d t h e o p e r a t i n g p o i n t demandedo f t h e e n g i n e . T h e turbine e x h a u s t i s thene x p a n d e d t h r o u g h th e nozzle t o add a smallcontribution t o t h e engine t h r u s t . This thrustcontribution f r o m g a s at r e l a t i v e l y l o w tempera-tures l o w e r s t h e overall s pe c i f i c i m pu ls e belowt h e s p e c i f i c impulse obtained from t h e main p r o -pellant f l o w which i s , o f course, a t a much h i g rtemperature than t h e turbine ex it g a s . On e useo f t h e turbine exhaust would b e to p r o v i d e c o o l -i n g f o r nozzle s k i r t extension i f r e q u i r e d andt h e n e x h a u s t i n g i t overboard t o p r o v i d e a smallthrust c o n t r i b u t i o n .

T h e major e m p h a s i s in t h e program to date h a sbeen on t h e r e a ct o r component o f t h e nuclearrocket engine s y s t e m . T h e p a s t r e a c t o r work willb e reviewed t o define t h e status of r e a c t o rtechnology wh ich h a s i m p r o v e d i m m e a s u r a b l y i n th el a s t s i x m o n t h s a s i s evident f r o m f o u r h i g h l ysuccessful r e a c t o r tests. T h e m a j o r d e v e l o p m e n tp r o b l e m s i n t h e r e a c t o r component have been t h edevelopment o f h i g h temperature materialstechnology f o r t h e f u e l elements contained i nt h e c o r e , t h e provision o f a d e q u a t e structurals u p p o r t , p r o o f o f control c a p a b i l i t y , andoperation with l i q u i d h y d r o g e n .Substantial progress h a s b e e n made i n t h ed e v e l o p m e n t o f r e a c t o r t e c h n o l o g y since the LosAlamos S c i e n t i f i c L a b o r a t o r y started its researcha n d d e v e l o p m e n t work i n 1 9 5 5 . T h i s e a r l y workl e d t o testing o f t h e KIWI-A series o f r e a c t o r s ,w h i c h , as indicated in F i g u r e 3 gave i m p o r t a n td e s i g n , materials and control and nuclearcharacteristics i n f o r m a t i o n . T h r e e KIWI-Areactor tests w e r e r u n in 1 9 5 9 a n d 1 9 6 0 .I n t h e K I W I - B l series reactor tests ru n i n1 9 6 1 a n d 1 9 6 2 , as i l l u s t r a t e d i n F i g u r e 4 theLASL s h o w e d t h a t t h e s e r e a c t o r s could be ef-f e c t i v e l y controlled b y t h e control drum in t h ereflector o f t h e reactor. I t w as also s h o w nthat t h e s e r e a ct o rs c o u l d b e o p e r a t e d withh y d r o g e n a s a coolant a n d with a l i q u i d h y d r o g e ncooled nozzle as would b e r e q u i r e d in f l i g h tr o c k e t s y s t e m s . D u r i n g t h i s time t h e Los Alamoss c i e nt i st s a n d engineers d e v e l o p e d methods f o rfabricating the u r a n i u m b e a r i n g fuel e l e m e n t swith g r a p h i t e as a structural m a t e r i a l ,inspection t e c h n i q u e s , an u n d e r s t a n d i n g o f t h eeffects o f t h e h i g h temperature on the n u c l e a rcharacteristics of t h e reactor, and a u t o m at ic

start-up o f reactors with l i q u i d hydrogen a s t h ec o o l a n t . S u c h items marked t h e substantialprogress an d advancement made during t h e yearssince t h e program started. Fo ll ow in g these B - 1series of reactors, t h e preferred reactor designand t h e one intended f o r th e NERVA engineapplication, t h e KIWI-B4A r ea ct or , w as tested i nNovember, 1 9 6 2 , with r es u lt in g d am ag e t o t h ereactor core due t o flow induced vibrations.Following t h e discovery o f a structuralproblem i n t h e KIWI-B4A t e s t , a n estensiveeffort w as instituted t o uncover t h e causes oft h e observed structural vibrations and t o designa n d t e s t solutions t o t h e p r o b l e m . Designstudies were instituted, component tests we rep e r f o r m e d , a n d , f i n a l l y , t h e redesigned KIWI-B4reactors were successfully tested i n t h e l a t t e rhalf o f t h i s year ( 1 9 6 4 ) .On e significant t e s t , shown o n Figure 5 , wa st h e KIWI-B4A c o l d f l o w reactor wh ich confirmedseveral important t h e o r i e s . This t e s t occurredi n M a y , 1 9 6 3 . A cold-flow reactor contains n ofissile materials a n d i t i s operated t o study i nd e t a i l , t h e f l o w characteristics within t h ereactor system without heat generation o r nucleareffects. Flow-induced vibrations occurred with-o u t t h e generation o f power i n t e s t s conductedwith gaseous n i tr og e n, h y dr og e n, a n d helium.T h e structural vibrations were induced b y t h ef l o w within t h e core a n d we re n o t due t o nuclearinteractions n o r caused b y unstable flow o r burn-i n g hydrogen within t h e nozzle.F u r t h e r confirmation o f t h e relation betweenf l o w conditions a n d structural v ib ra ti on s w e reo bt ai ne d w i th t h e KIWI-PIE experiment, shown o nFigure 6 a one-sixth segment o f a complete c o r e .T h i s d ev ic e, w hi ch w a s designed f o r flexibilitya n d testing simplicity, has been used a t LASL t os t u d y design improvements. A test-rig havingsimilar c a p a b i l i t i e s h a s been operated a tW e s t i n g h o u s e t o s t u d y flow characteristics i n t h eWANL design o f t h e NERVA reactor.Cold-flow r ea ct or s, b ot h K I W I a nd NE RV A, weretested t o confirm design changes made t o elimi-nate structural vibrations. T h e n , i n M a y , 1 9 6 4 ,t h e KIWI-B4D was tested near rat ed conditions f o ra s h o r t t i m e until a l e a k i n t h e nozzle occurreda n d terminated t h e t e s t . Fortunately, t h e nozzlef a i l u r e did n o t compromise attainment o f t e s to b j e c t i v e s . Causes f o r t h e nozzle failure haveb e e n narrowed down t o one o r t w o p o s s i b i l i t i e s ,wh ich were eliminated through s o m e simplemodifications t o nozzles used i n future reactort e s t s .Another significant event occurred i n Augustwith t h e s u c c e s s f u l t e s t of t h e KIWI-B4E reactor,F i g u r e 7 . T h i s t e s t l a s t e d f o r e i g h t minutes,t h e l e n g t h of t i m e permitted b y t h e l i q u i dhydrogen storage capacity of t h e reactor t e s tc e l l . Th e reactor w a s operated a t t h e plannedh i g h p o w e r a n d temperature conditions i n athoroughly s uc ce ss fu l f as hi on with t h e resultingconclusion t h a t t h e reactor design i s sound a n d

1 9 6 5 1 6 1


3/9

IEEE TRANSACTIONS ON NUCLE R SCIENCEsuitable f o r use in a nuclear rocket e n g i n e .

After a wait of 1 3 d a y s , t h i s KIWI-B4Ereactor was restarted and operated f o r 2 . 5minutes more a t the planned h i g h temperature andpower c o n d i t i o n s . This most vital test showedt h e feasibility o f restarting graphite reactors.A l s o , i n September, t h e NERVA contractorsoperated a NERVA reactor, a version o f t h e KIWIreactors, n e a r r a t e d conditions f o r severalminutes. T h i s reactor was also restarted f o r o p -eration a t l o w p o w e r l ev e l s t o o bt ai n n uc le arcontrol characteristic d a t a .T h e method o f t es ti ng r ea ct or s i s worthmentioning because i t bears o n t h e overallprogress a n d status o f t h e p r o g r a m . F i r s t , t h ereactors a r e started automatically, from s u b -critical conditions t o t h e megawatt power rangei n much l e s s t h a n a m i n u t e . T h e n propellant f l o wi s initiated a n d power a n d f l o w rate a reprogrammed t o increase from t h e low-levels t or a t e d conditions i n time p e r i o d s a l so l e s s t h a n

a minute. T h e reactors are tested with regener-atively cooled nozzles a s would b e done i n a ne n g i n e . T h e l i q u i d - h y d r o g e n i s s u p p l i e d b y ah i g h p e r f o r m a n c e , turbine-driven p u m p . T h u sseveral o f t h e features o f a f u l l e ng in e s ys te mh a v e already been incorporated i n t h e reactort e s t s .T h e s e reactor tests a re major milestones i nt h e Nuclear Rocket Program. A f i r m b a s e f o rf u t u r e development work h a s b e e n e s t a b l i s h e d ;h o w e v e r , additional R D i s r e q u i r e d to make t h ereactors operate f o r l o n g e r p e r i o d s o f t i m e , ath i g h e r temperatures, a n d at h i g h e r p o w e r l e v e l s .In t h e NERVA t e c h n o l o g y p r o j e c t , t h e r e a rem a n y o t h e r activities i n addition t o r e a c t o rd e v e l o p m e n t . A m o n g t h e s e i s t h e w o r k on t h epropellant f e e d system, which consists o f t h eturbopump a s s e m b l y , propellant l i n e s , t h e tank-shut-off v a l v e , and t h e t u r b i n e - p o w e r - c o n t r o lvalve. Its purpose i s t h e d e l i v e r y o f h y d r o g e nat controlled rates o f f l o w a n d pressure to t h eremainder o f t h e engine. T h e t u r bo p u m p a s se m b l y,Figure 8 consists o f a s i n g l e - s t a g e c e n t r i f u g a lpump driven b y a m u l t i - s t a g e , axial-flow t u r b i n e .T h e pump delivers 7 0 l b / s e c o f h y d r o g e n f l o w .Bearings are cooled and lubricated with L H 2 andare r e g a r d e d a s a s i g n i f i c a n t area o f d e v e l o p -m e n t . E x p e r i m e n t a l engine g r o u n d tests will b eo p e r a t e d with such a t u r b o p u m p assembly.Components o f t h e p r o p e l l a n t f e e d system h a v eb ee n u nd er development since t h e NERVA p r o j e c tb e g a n . Characteristics of the turbopump-assemblyhave been determined experimentally using bothcold and h o t turbine drive g a s e s . Th e b e a r i n g shave been tested under simulated l o a d s in l i q u i dhydrogen f o r several h o u r s . Bearings have alsob e e n t e s t e d under l o a d , in l i q u i d h y d r o g e n , andi n a n u c l e a r r ad i at io n field at t h e NuclearAerospace Reactor Facility ( N A R F ) wh ich G e n e r a lDynamics/Fort W o r t h , T e x a s , operates f o r the Ai rForce. Encouraging r e s u l t s have be en obtained

i n t h e 15-20 m in ut e t es ts run t o d a t e . Longerruns are s c h e d u l e d . T h e turbopump c on tr ol v al veh a s also been tested t o prove satisfactoryo pe ra ti on w it h h ot -g as f l o w .T h e t hr us t c ha mb er assembly c on si st s o f t h ethrust structure, t h e pressure v e s s e l , a n d t h enozzle. Nozzles h av e p ro ve n t h e m o s t difficultd ev e lo p me n t p r ob le m i n t h e Nuclear Rocket P r o g r a m .Nozzle development i s proceeding with a signifi-cant amount o f e f f o r t devoted t o i t . Th eRocketdyne n o z z l e , Figure 9 , was employed o n t h eK I W I tests a n d will b e used o n s o m e Phoebusreactor t e s t s . T h e tubes wh ich f o r m t h e c o o l e d,convergent-divergent f l o w passage f o r gasesleaving t h e reactor a re c le ar ly v i s i b l e . T h erugged nozzle pressure vessel required t o with-s t a n d the static pressure l o a d s i s also s h o w n .Figure 1 0 i s a p h o t o o f a n Aerojet-General NERVAnozzle rigged with a n adapter a n d c he mi ca l r oc ke tinjector t o p e r m i t simulation t e s t s t o b e p e r -f o r m e d with a c he mi ca l r oc ke t f i r i n g . A n y nozzledesign m u s t consider f u l l y :a ) t h e high h e a t t ra ns fe r r at es from t h e mainexhaust stream t o t h e nozzle coolant tubesdue t o h i g h h e a t conductivity o f hydrogen;b ) t h e use o f hydrogen a s propellant, wh ichrequires exclusion o f air f r o m t h e nozzlea nd p re ve nt io n o f any hydrogen l e a k a g e ;c t h e l a r g e contraction ratio i n t h e c o n -vergent section t o provide a transitionfrom t h e reactor outlet diameter t o t h et h r e a d d i a m e - t e r . T h i s high r a t i o ,peculiar t o nuclear r o c k e t s , results i nl a r g e tangential and longitudinal stresseswhich must b e contained b y t h e nozzlepressure s h e l l .

O u r current e f f o r t s in nozzle d e s i g n a n d develop-ment include:a ) efforts t o estimate, more accurately, heattransfer characteristics f r o m t h e h o te x h a u s t t o t h e nozzle coolant leading t odetermination o f temperatures a n d stressesin n oz zl e c oo la nt t u b e s ;b ) investigation o f alternative designs andmaterials to provide added marginsbetween o p e ra t in g t e mp e r at u re s a n dmaterials c a p a b i l i t i e s ;c ) determination o f energy deposition ratei n pressure s h e l l a n d a s s u r a n c e o fadequate c oo li ng p r ov is io ns t o maintainthe pressure s h e l l at a n acceptabletemperature; andd ) investigation of fabrication and qualitya s s u r a n c e t e c h n i q u e s wh ich a l l o w fabri-c at io n a nd a s s u r a n c e t h a t nozzles a rebuilt a s r e q u i r e d to withstand alloperating conditions. This p r a c t i c a la r e a represents our major problem area.A s part of this problem, t h e difficulty

1 6 2 F e b r u a r y


4/9

SCHWENK: SOLID CORE NUCLEAR ROCKETSof simulating operating conditions s h o u l db e pointed o u t h e r e .

Nozzle development f o r t h e nuclear rocket i sproceeding with a significant amount of effortdevoted t o i t . However, we h a v e not a s yetobtained a nozzle design with sufficient demon-strated reliability t o meet all of the r e a ct o rand engine t e s t requirements including reason-able f l i g h t type operating capabilities.

Testing o f a complete nuclear rocket enginesystem i s extremely vital to t h e d e v e l o p m e n t o fnuclear rocket t e c h n o l o g y . Three types o fsystems tests ar e p l a n n e d f o r N E R V A . A c o l d f l o wversion o f a complete nuclear rocket engine willb e tested i n t h e H-area t e s t complex at Aerojet-General s h o w n i n Figure 1 1 . T h i s c o m p l e x h a sseveral test positions f o r nozzle and t u r b o p u m pcomponent testing a s well a s system test capa-b i l i t y . T h e system t e s t position i s underneaththe l a r g e l i q u i d hydrogen run t a n k . Testingunderway a t t h e Lewis Research Center of NASA i salso p r o v i d i n g information a b o u t t ra n s i e ntcharacteristics of g e n e r a l i z e d nuclear rockete n g i n e .T h e s e c o n d engine system i s b ei n g d e s i g n ed toinvestigate engine systems characteristics b ym o d i f y i n g t h e reactor c o n f i g u r a t i o n s tested int h e reactor t e s t c e l l s . We p l a n to install aturbopump an d h o t bleed nozzle on a test car inconjunction w i t h a NERVA reactor test. T h eassembly i s t h e n an engine system e x p e r i m e n t ;h o w e v e r , t h e engine f i r e s u p w a r d with t h e nozzleexhausting into t h e a t m o s p h e r e . T h e s t a r ttransients are obtained under h i g h backpressureconditions. T h i s test system will a l l o w us t os t u d y startup characteristics a n d obtain oper-ating data i n p a r t s o f t h e s t e a d y state e n g i n eoperating m a p .T h e t h i r d system test will b e conducted i nETS-1 ( F i g u r e 1 2 ) which can test a nuclear rocketengine i n t h e d o w n w a r d f i r i n g p o s i t i o n with a l lcomponents i n their proper location. A 7 0 , 0 0 0g a l l o n LH2 run t a n k is l o c a t e d above t h e e n g i n ec h a m b e r . An e x h a u s t duct i s c o n t a i n e d in t h echamber below t h e engine c h a m b e r .T h e a d v a n c e d g r a p h i t e r e a c t o r program( P h o e b u s ) i s conducted b y t h e LASL with t h eo b j e c t i v e s o f d e v e l o p i n g r e a c t o r t e c h n o l o g y t oprovide l o n g operating t i m e s , h i g h s p e c i f i ci m p u l s e , restart c a p a b i l i t y , a n d h i g h p o w e rl e v e l s . T h e r e a r e p l a n s to test a 5 0 0 0 M W , al a r g e diameter r e a ct o r ( P h o e b u s - 2 ) i n s e v e r a lyears. T h i s d e s i g n power l e v e l was s e l e c t e d ont h e basis o f mission s t u d i e s , reactor t e c h n o l o g y ,facility p r o b l e m s , and component a v a i l a b i l i t y .Consideration was also given t o clustering in t h esize-selection. A s p a c e - c r a f t p o w e r e d b y acluster o f f o u r nuclear r o c k e t engines is i l l u s -strated in F i g u r e 1 3 . C l u s t e r i n g affords greatf l e x i b i l i t y i n the application of a s i n g l e engine

t o several p h a s e s o f o n e m i s s io n and to differentmissions. 2

Research o n clustering i s , t h e r e f o r e , a vitalportion o f t h e Phoebus p r o g r a m . Analyses o fnuclear interaction have been made a n d , recently,LASL h a s completed a significant s e r i e s o fcritical experiments Figure 1 4 ) i n which t w or ea ct or s w er e t e s t e d a t l o w p o w e r l e v e l s i n closeproximity t o each o t h e r .

T h e Phoebus program involves design s t u d i e s ,component t e s t s , materials r e s e a r c h , a n d reactorp h y s i c s s t u d i e s . I n addition, LASL w i l l conducts e v e r a l P h o e b u s - l reactor tests w hi ch u ti li zeKIWI hardware. These experiments w i l l permitaccumulation o f important design data a t a n earlyt i m e a n d with minimum c o s t . First o n e scheduledf o r early n e xt y e a r .T h e Phoebus reactor design i s based o n t h eKIWI technology; however, a great number ofdesign improvements are p l a n n e d f o r Phoebus-2reactors. T h e engine t o b e developed from t h el a r g e Phoebus-2 reactor w i l l benefit greatlyf r o m t h e NERVA d eve lop m e nt . A s a consequence,we h a v e great confidence i n o u r capability t odevelop t h e h i g h - p o w e r nuclear rocket enginesrequired f o r space missions.T h e h i g h melting p o i n t a n d s t r e n g t h proper-t i e s o f tungsten encourage consideration of t h i smaterial a s a candidate f o r nuclear rocketreactors. Another consequence, we are conducting

a research program t o e s t a b l i s h t h e performancepotential o f reactors using tungsten a s a f u e lelement. Most o f t h e work i s on f u e l materialsr e s e a r c h a n d f a b r i c a t i o n t e c h n o l o g y , because i fa tungsten f u e l element cannot b e p r o v i d e d atungsten reactor cannot b e d e v e l o p e d . T h e out-s t a n d i n g p e r f o r m a n c e f e a t u r e s which motivateinterest i n tungsten reactors f r o m an applicationss t a n d p o i n t are t h e p o t e n t i a l f o r very l o n g oper-ating durations a n d t h e possibility o f developinga s m a l l , l i g h t - w e i g h t engine f o r l o w t h r u s tl e v e l s ( a p p r o x i m a t e l y 1 0 , 0 0 0 l b s ) .

T h e program o n tungsten reactors f o r nuclearrockets i s c e n t e r e d on two r e ac t or c o nc ep t s.T h e Argonne N a t i o n a l Laboratory o f t h e AEC i sexploring a f a s t concept. T h e NASA LewisResearch Center i s conducting a program t o e x -plore t h e f e a s i b i l i t y o f a t h e r m a l , water-moderated tungsten reactor. T h e m o s t significantdifference between t h e s e two reactor concepts i si n t h e area o f uranium l o a d i n g i n t h e f u e lelements; i . e . , t h e percentage o f uranium dioxidewhich must b e p l a c e d i n t h e s t r u c t u r a l material,t u n g s t e n , t o m e e t criticality requirements. Th ef a s t reactor requires h i g h f u e l l o a d i n g s i n t h erange o f 5 0 v ol um e p er ce nt o f U02 and above.T h e t h e r m a l reactor, h o w e v e r , ma y require f u e ll o a d i n g s below 3 5 volume p e r c e n t . T h i s differ-e o c e i n f u e l l o a d i n g may b e critical i f t h i sparameter becomes t h e m o s t significant factor i nestablishing f u e l properties and determiningwhether a feasible f u e l fabrication process c a nb e developed.

In order to achieve criticality with very lowf u e l loadings, t h e thermal reactor must b e made

1 9 6 5 1 6 3


5/9

IEEE TRANSACTIONS ON NUCLEAR SCIENCEwith t u n g s t e n enriched i n the l o w cross-sectioni s o t o p e , tungsten 1 8 4 . T h e requirement f o r l o wn e u t r o n absorbing cross-section also eliminatest h e p o s s i b i l i t y o f u t i l i z i n g m a n y o f t h e k n o w na l l o y i n g elements w h i c h t e n d t o alleviate t h eb r i t t l e nature o f t u n g s t e n . F o r e x a m p l e , rheniuma n d t a n t a l l u m , which a r e often u s e d a s a l l o y i n gagents i n t u n g s t e n , a r e barred from considerationo f t h e t h e r m a l r e a c t o r b u t c a n b e e m p l o y e d i n af a s t reactor because o f t h e i r high t h e r m a ln e u t r o n c r o s s - s e c t i o n . O n t h e o t h e r h a n d , t h el o w f u e l l o a d i n g i n t h e t h e r m a l r e a c t o r m a yp r o v i d e s o m e unique a d v a n t a g e s i n f u e l f a b r i -c a t i o n a n d i n f u e l p r o p e r t i e s .

T h e t u n g s t e n r e a c t o r program i s c o n c e n t r a t i n go n f u e l technology a n d , within a p e r i o d o f t w oy e a r s , w e s h o u l d a c q u i r e s u f f i c i e n t d a t a t o j u d g et h e f e a s i b i l i t y a n d p e r f o r m a n c e p o t e n t i a l o ft u n g s t e n r e a c t o r s f o r n u c l e a r r o c k e t a p p l i c a t i o n s .I n s u m m a r y , t h i s p a p e r h a s described b r i e f l y ,

t h e p r o g r a m s underway t o develop s o l i d - c o r er e a c t o r t e c h n o l o g y f o r n u c l e a r r o c k e t s . R e c e n ts u c c e s s f u l K I W I a n d NERVA r e a c t o r s h a v e s h o w ng r e a t p r o g r e s s i n t h e development o f graphiter e a c t o r t e c h n o l o g y a n d p r o v i d e a s o u n d b a s i s f o r

t h e ultimate d e v e l o p m e n t o f nuclear rockete n g i n e s f o r a v a r i e t y o f space m i s s i o n s . I naddition t o t h e reactor w o r k, t h i s d i s c u s s i o np r e s e n t e d t h e e f f o r t s i n t h e Nuclear R o c k e tP r o g r a m f o r d e v e l o p m e n t o f non-reactor com-ponents, systems s t u di e s a nd r e s e a r c h , a n d f u l lnuclear rocket engine systems tests ( t o b econducted i n t h e n e x t two or t h r e e y e a r s ) t oprovide t h e overall technology required f o rapplication o f s o l i d - c o r e nuclear r o c k e t e n g i n e st o missions.

R e f e r e n c e s :1 . Finger, H a r o l d B . , NUCLEAR SPACE PROPULSIONS Y S T E M S . AIAA Paper N o . 6 4 - 5 5 6 . Presenteda t International Council of t h e Aero-nautical S c i e n c e s , Paris, France, A u g u s t2 4 - 2 8 , 1 9 6 4 .2 . J o h n s o n , Paul G . , A SUMMARY OF NUCLEAR

ROCKET A P P L I C A T I O N S . AIAA Paper N o .6 4 - 3 8 8 . Presented a t 1 s t AIAA AnnualMeeting, W a s h i n g t o n , D . C . , J u n e 2 0 - J u l y 2 ,1 9 6 4 .

1 6 4 F e b r u a r y


6/9

NERVA

MOCKUP

4

1

e

m

PROGRESSIN

KIWIA

REACTORS

1.

DESIGN

METHODS

2.

MATERIALDATA

3.

CONTROLINFORMATION

4.

NUCQEARCHARACTERISTICS

Fig.

3ProgressinKIWIAreactors

PROGRESS

IN

KIWI.11

REACTORS

1.

RIFLECTOR

CONTROL

2.

LIOUID

2

OPERATION

3.

LIQUIDN

COOLEDNOZZLE

4.

FUEL1ELEMET

AICATION

5.

AUTOMATICCONTROL

v

l

Fig4ProgressinKIWIBlreactors

C01

En z 0r0 co tTj z-I 2 n 01 C

Fig.

2Nuclearrocketengine.


7/9

KIWIB4EREACTOR

ATTESTCELLC

Fig5KIWIB4ACF.

Fig7KIWIB4Ereactor

MARKTHREETURBOPUMP

Fig8MarkIII

turbopump.

w CiH z 0 z t t c P 17

Fig.

6KIWIPIEatLASL.


8/9

NJ

:

|AEROJETGENERAL

r1MO

^7X

solid core rockets

Documents

Transcript of solid core rockets