Tài liệu Experience gained from the space nuclear rocket program (rover)

LA-10062-H History - . . ,... 1. . -- Experience Gained from the Space Nuclear Rocket Program (Rorer) ' <./ �,·_ .. > For Reference Not to be taken from this room n IA\� !{} n� rnr;l(R\ o .� �� �U@u u 'W:V� 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 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. 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 • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • . • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • . • • . • • • • • . • • • • • • • • • • • • • • • • • • • • • • 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 • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • . • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • . • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • . • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 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 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • . . • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • 10 11 13 16 16 17 18 19 21 21 21 21 22 23 VI I . ACK NOWL E DGME NTS VII I . SUPPLEMENTAL B I BL IOGRAPH Y ••••••••••••••••••••••••••. ••••••••••••••••• 24 REFERENC ES TAB LES • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • . . . • • . . • . . • . . FI GURES • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . . • . • . . . . . . . • • . . • . . . • • • . . . . • . • • • . . . . . . . . . . . • • • . . • . . . . . • . . . . . . . . . . • . • . . . . • . . • . . . . • . . . . . • . . . . . . . . . . . . . . . • . • . • • . • • . • • • . . . . . . • . • • 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