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S T I M U L A T I O N O F T H E D E V E L O P M E N T O F S O D I U M - C O O L E D F A S TR E A C T O R S

V . M . M u r o g o v , V . I . S u b b o t i n , V . S . K a g r a m a n y a n , V . M . P o p l a v s k i i ,N . S . R a b o t o n o v , a n d M . F . T r o y a n o v UDC 621.039.526.034.63

Co n s i d e r a b l e m a t e r i a l a n d i n t e l l e c tu a l r e s o u r c e s h a v e b e e n i n v e s t e d in p r o g r a m s f o r t h e d e v e l o p m e n t o f s o d i u m - c o o l e df a s t re a c t o r s o v e r a p e r i o d o f m o r e t h a n 4 0 y e a rs . Th e y h a v e n o w b e e n s u f f i c ie n t ly p r e p a r e d a t t h e s c i e n t if i c a n d t e c h n i c a l le v e lf o r s p e ci f ic d e s ig n wo r k , c o n s t r u c t i o n , a n d o p e r a t i n g t o b e c o n t i n u e d , i n c o r p o r a t i n g i n t e r n a t i o n a l e x p e r i e n c e [ 1 ].

Th e e x p e r i e n c e i n o u r c o u n t r y is f r o m f o u r o p e r a t i n g r e a c t o rs : BR- 1 0 , BOR - 6 0 , BN- 3 5 0 , a n d BN- 6 00 . A m a j o r c o n t r i b u -t ion i s be ing made by the BN-600 [2 , 3] , which has good ins ta l l ed-capac i ty u t i l i za t ion fac tors ( ICUF) , as wel l has a h igh l eve l ofnuc lear an d ra dia t ion safe ty : low pressu re and n o l eaks in the pr im ary loop, s t ab le nega t ive reac t iv i ty feedbacks , e f fec t ive hea tt ransfer by the t r ansfer , inc luding na tura l c i rcula t ion dur ing cool ing . Subs tant i a l ly be low the a l lowable ecologica l e f fec t of f as treac tors .

A h i g h b u r n - u p o f o x id e f u e l h a s b e e n a t t a i n e d i n f a st r e a c to r s : u p t o 1 2 % i n BN- 6 0 0 , u p t o 2 0 % i n Ph e n i x ( F r a n c e ) ,a n d PFR ( Gt . Br i t a i n ), a n d u p t o 1 8 % i n m e t a l a l lo y te s t f u el e le m e n t s i n t h e USA . Co n s i d e r a b l e e x p e r ie n c e i n p r o d u c in gu r a n i u m - p l u t o n i u m o x i d e fu e l a n d s u b s e q u e n t r e p r o c e s s in g o f t h e s p e n t f u e l h a s b e e n g a i n e d in F r a n c e a n d G t . Br i ta i n . Th ePh e n i x a n d PFR r e a c t o r s h a v e a l r e a d y b e e n o p e r a t e d o n m u l t i p l y r e g e n e r a t e d f u e l . Ur a n i u m o x i d e f u e l wi t h a c c u m u l a t e dp l u t o n i u m f r o m t h e B N- 6 0 0 i s r e p r o c e s s e d r e g u la r ly . Sm a l l b a t c h e s o f m i x e d o x i d e fu e l a r e p r e p a r e d a t t h e " M a y a k " I n d u s t ri a lAm a l g a m a t i o n a n d t h e S c i e n t i fi c - Re s e a r c h I n s t it u t e o f At o m i c Re a c t o r s .

Th e p r o b l e m o f e x p a n d e d b r e e d i n g h a s c e a s e d t o b e t i m e l y u n d e r t h e p r e s e n t c o n d i t i o n s i n t h e n u c l e a r p o we r i n d u s t r y .Th e BN-800 pro jec t , for example , is charac te r i zed by suf f i c i ent breed ing for p lu to nium se l f - suf f i c iency (breeding ra t io B R - 1) .I t m u s t b e n o t e d t h a t e v e n wi t h BR - 1 a f a s t r e a c t o r h a s a f u n d a m e n t a l a d v a n t a g e o v e r t h e r m a l r e a c t o r s i n re g a r d t o n a t u r a lu r a n i u m c o n s u m p t i o n . T h e o p e r a t i o n o f s u c h a r e a c t o r r e q u i re s a n i n it i al c h a r g e a n d t h e r u n n i n g p l u t o n i u m c o n s u m p t i o n i sb a l a n c e d b y p l u t o n i u m b r e e d i n g a n d t h e i n v o l v e m e n t o f a s m a l l a m o u n t [ - 1 t o n U/ G W ( E ) y r ] o f u r a n i u m . I n v ie w o f t h e l a rg ea c c u m u l a t e d r e s e r v e s o f b o t h u r a n i u m a n d p l u t o n i u m , i t c a n b e s a i d t h a t t h e o p e r a t i o n o f t h e BN- 8 0 0 , , i n c o n t r a s t t o t h e r m a lr e a c t o r s , d o e s n o t r e q u i r e n a t u r a l u r a n i u m o r s e p a r a t i o n .

Economy and Safe ty of Fas t Reac tors . The spec i f i c capi t a l out l ays and e lec t r i c i ty product ion cos t s of the f i r s t p i lo treac tors were 1 .5-2 .5 t im es those of present -day l ight -water reac tors . D om es t i c [4] and fore ig n [5] ana lys i s shows tha t th esed i f fe r e n c e s a r e c a u s e d o n l y t o a s m a l l d e g r e e ( wi t h in 2 5 % ) b y t h e s p e c i fi c s o f s o d i u m t e c h n o l o g y a n d m u c h m o r e s o b y o t h e rfactors:

- out l ays for a t t a in ing a h igh degree of sa fe ty ;- the t echn ologica l mas te ry , i. e ., is the reac to r comm erc ia l or se r ia l ;- t h e r e g i o n o f c o n s t r u c t i o n a n d t h e m a s t e r y o f t h e s it e;- t h e c a p a c i t y a n d n u m b e r o f p o we r u n i t s o n t h e s i t e ;- t h e t i m e r e q u i r e d t o p r e p a r e t h e p r o j e c t a n d b u i l t a p o we r u n i t ; a n d- t h e d e g r e e o f d e v e l o p m e n t o f t h e f u e l c y cl e t e c h n o lo g y , t h e c a p a c i t y a n d u t i l i z a ti o n f a c t o r o f t h e f u e l s u p p l y e n t e r p r is -es, etc.Th e e x p e r i e n c e f r o m o p e r a t i n g t h e BN- 6 0 0 wa s t a k e n i n t o a c c o u n t i n t h e BN - 8 0 0 d e si g n . Th e s p e c i fi c m e t a l c o n t e n t o f

t h e l a t te r i s 7 9 % [ 3] o f t h a t o f t h e BN- 60 0 ; t h e n e w BN- 6 0 0 M d e si gn , d e v e l o p e d a t t h e OK BM ( En g i n e e r i n g Te s t i n g - De s i g nBu r e a u ) , h a s a s p e c i f ic m a t e r i a l c o n t e n t o n a p a r wi t h t h o s e o f t h e n e w - g e n e r a t i o n in t e r m e d i a t e - c a p a c i t y VV I ~R ( wa t e r - m o d -e r a t e d wa t e r - c o o l e d p o we r ) r e a c t o r VPBt ~R- 6 0 0 [ 6 ] .

Phys ics and Pow er Engin eer ing Ins t i tu te . Trans la ted f ro m Atom nay a t~nergiya , Vol . 74 , No. 4 , pp . 286-290, Ap r i l , 1993.

268 1063-4258/93/7404-0268512.50 1993 Plen um Publ i sh ing Co rpor a t ion

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TA BL E 1 . Time Varia t ion o f the Rela t ive Toxic ity Indices wi th Al lowance for the Con tr ibut ionf ro m D a u g h te r N u c lid e s Fo rme d D u r in g S to ra ge *

Nucl ide

238pt239pu24Opu241pu242pu~TNp241Am243Am244Cr

H a l f - l i f 0 , S t or age t i me , yryr I0 100 1000 10000

87;724000656014,4370.103210.10443 2737018,1

2231

3, 6450.050,02

633,3

60 0

1101

3, 6560,050,02

543,3

20

0,30,973,3

130,050,02133,13,3

1,50,751,30,020,050,020,021,81,3

*The ca lcula t ions were don e by A. G. Tsikunov, A. L. K oche tkov, and V. S . Kagramyan.

The impr ovem ent in the fue l cyc le econo my of fast reac tors i s de te rmined by the increase in fue l burn-up in the reac torcore to 15-20% and the c rea t ion of la rge-sca le au tom ated prod uc t ion of urani um -pl u to niu m fuel . The BN -600 is a l readycompet i t ive wi th convent iona l energy sources.

The m ore s t r ingent sa fe ty requirements br ing the eco nom ic indica tors of fast and thermal reac tors c loser toge ther s incein fast reac tors these requirem ents a re met by s impler means as a resu l t of the low pressure in the sodium loops, easie r contro lof the reac tor g iven the com pensa t io n o f burn-up, th e s tab i l ity of the energy-re lease f ields, e tc .

The inherent proper t ies of fast reactors as wel l as the in t roduc t ion o f addi t iona l technica l fea tures (passive means ofac t ing on the react iv ity , a system of emergency cool ing through a i r hea t exchangers , a sum p for co l lec ting mol ten fue l ) havebrought up the B N-800 pro jec t to a level tha t mee ts the requiremen ts of new-genera t ion nuc lear power p lants. In par t icu la r , thepositive sodium reactivity void effect when sodium boils has been eliminated in this reactor.

Enh ance men t of the sa fe ty of wate r-m odera ted wate r-cooled power reac tors required new projec ts : the VVt~R-500 ( theNP-500 pro jec t ) and the VPBI~R-600 ( the NP-600 pro jec t ) . T he la test econom ic est imates have shown tha t the spec i f ic capi talout lays on the co nst ruc t ion of the main uni t and three subsequent uni ts (averaged over the four uni ts) wi th NP-500 and BN-800reac tors a re a lmost equa l . These resul ts confi rm ear l ie r predic t ions.

The e ff ic ien t use of p lu tonium in fast reac tors wi l l mean savings of enr iched uranium in the nuc lear pow er indust ry andan expansion of exports of enr iched uranium as fue l for nuc lear power p lants.

Burn ing of Aet in ides. Transuran ium e lements (p lu tonium, neptunium, americ ium, and cur ium) bui ld up dur ing opera-tion of the reactors. Plu ton ium has always been con sidere d as an artificial nuclear fuel. Mo reover , these actinides, includingplu tonium iso topes, a re long-l ived , main ly a -emit t ing , and substant ia l ly compl ica te the u l t imate bur ia l of nuc lear power wastes ,Table 1 shows how the spec i f ic rad io toxic i ty of var ious ac t in ides vary wi th t ime during pro longed storage . The s tand ard chosewas the b io logica l rad io toxic i ty of t he pr inc ipa l ac t in ide , 239pu, defined as the volume o f wate r necessary to d i lu te a uni t mass ofa sample to the maximum a l lowable concentra t ion .

Table 2 shows tha t in a thousand years of s torage of spent nuc lear fue l the main contr ibut ion to the to ta l rad io toxic i tyof the ac t in ides comes f rom 241pu and i t s decay produc t 241Am. In the short te rm 238pu and 244Cm are significant. When theac t in ides a re rem oved fr om the wastes the to ta l rad io toxic i ty of the remaining f ission fragments becomes the same as tha t ofuranium ore in severa l hundred years; o therwise, hundreds of thousands o f years are required for th is to happen.

In the past severa l years exper ts have focused constant a t ten t ion on the possib i l i ty of dest roying ac t in ides produced inreac tors by put t ing them in h igh- in tensi ty neutron f luxes. Two te rms have been used ~0 denote th is process: t ransmuta t ion andburning . The f i rs t is more genera l; i t i s the te rm used for any t ransformat ion of a long-l ived nuc l ide in to another (pre fe rablystable, rapidly decaying, or less radiotoxic).

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TA BL E 2 . C o n t r ib u t io n o f V a r io u s N u c l id e s t o t h e Ra d io to x ic i ty o f t h e A n n u a l Sp e n t U ra n i -um F uel f ro m a PWR -1000 R eac tor (33 GW .day/3rr

N u c l i d e237Np2.38pu .~gp u240pu241pu + 241Am242pu

Pu + 241Am243Arli244CmTotal

Nuclide production,kg/yr113, 4126,158,131,711,82312, 20, 624 5

Radiooxicity as a function of thestorage time, kg.equiv. 2 s ~u3 y r0, 286 2126

2 1 511610, 62365746 42836

1000 y r0, 21,012219241 20, 672 76, 81,9737

Burning today is used to de note f i ss ion . The consis ten t d i f fe rent ia t ion be tween these two types of processes i s a newpheno meno n. This d i f fe rence is the key to an understanding of the quant i ta t ive d i f fe rence, t ransforming in to a qua l i ta t ivedifference, be tween the resul ts of ac t in ide recyc l ing in fast and thermal reac tors. I t is de te rmined by h igher ra t ios of the averagef ission and capture c ross sec t ions for threshold e lements in fast reac tors than in thermal reac tors . From the s tandpoin t ofobtaining energy this is not crucial since there is one natural actinide nucleus (235U) and several artificial actinide nuclei, whichare easily fissioned by therm al neu trons. It is crucial, however, for a device, one pur pos e of which is to transf orm all the actinidesin to f i ss ion f ragments . Le t us consider th is on the co mputa t io na l example o f a h igh-flux thermal-neutro n e lec t ronuc lear fac il ity ,t h e Lo s A la mo s A TW p ro je c t [7] .

The main task of the AT W is to burn p lu toniu m as well as neptunium and americ ium. The ir to ta l re la t ive concentra t ionin the fue l does indeed d ecrease by a fac tor of 1 .5 . At the same t ime , however , the cur ium c oncentra t ion (mainly 244Cm and248Cm) increases 1000 times, to 38%. T his can scarcely regarde d as a satisfactory result of transm utati on since the inter-mediate-lived 244Cm is highly active and releas e m uch heat, while 248Cm is exceptionally radiotoxic since 8% of i ts decays arespontaneous fission and its half-life is 340,000 yr. Its thermal and capture cross sections, and especially its fission cross section,a re low and i t can be t ransm uted only wi th d i f ficul ty. The bui ldup of threshold nuc l ides, pr imari ly even iso topes of cur ium,de te rmines the pr inc ipa l d isadvantage of thermal reac tors as burners of ac tin ides tha t bui ld up dur ing recyc ling; the radio toxici tygrows with time.

In comp arison wi th o ther methods, burn ing of neptunium, americ ium, and cur ium is most e ff ic ient in fast reac torswhere , in contrast to th ermal reac tors , the to ta l mass and radio toxic i ty of the t ransura nium e lements in the system stabi l ize fa ir lyrapidly dur ing recyc l ing [8] . Only f iss ion produc ts and t ransuranium e lements lost dur ing chemica l processing of the spentnuc lear fue l would ente r the wastes in th is case . The necessary reduc t ion of the loss of t ransuran ium e lements can be achievedby in t roduc ing e ff ic ien t chemica l processing methods to ex t rac t 0 .99 to 0 .999 of the var ious types of nuc l ides.

Studies show tha t fast reac tors can burn neptunium , am eric ium, and cur ium bui ld in them and in thermal reac tors .Wh en 3 .5% ac t in ide oxides a re added to the fue l of the BN-800, wi thout apprec iably a ffec t ing the reac tor charac ter is t ics , theac t inide oxides a re burn ed a t the ra te o f 100 kg/yr . This means tha t on e BNL800 can in addi t ion burn the neptunium , americ ium,and cur ium bui l t up in three or four VVI~R-1000 [9] . They can a lso be burned a t a faste r ra te in a custom-bui l t fast reac tor .

Use of Bui l t -Up Plu toniu m. Opera t ion of reac tors produces a considerable amoun t of nuc lear-power-grade p lu tonium,a large par t of which a t present i s concentra ted in reposi tor ies of spent fue l f rom R BM K and VV]~R-1000 reac tors . In ourcountry p lu tonium is a lways considered an energy resource for nuc lear power . This was the basis for the const ruc t ion (a longt ime ago) of the R T-1 p lant for chemica l reprocessing of spent fue l , main ly f rom the VVt~R-440. Uran ium fue l f rom th e BN-600is a lso reprocessed . Up to the present m ore than 25 tons of nuc lear-power-grade p lu ton ium has been extrac ted. I t s pro longedstorage enta ils de te r iora t ion of i t s qua l ity becaus~ of the decay of 241pu in to the ecologica l ly more dangerous 241Anl .

Convers ion is expec ted to f ree tens o f tonnes of weapons-grade p lu tonium. Like the nuc lear-pow er grade , i t can be usedfor energy produc t ion [10] .

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The fact that the prog ram for using nuclear-power-grade and weapons-grade plutonium has not yet been substantiatedscientifically and ecologically has aroused the anxiety of both experts and the public since i t aggravates the p roble m of nonp rolif-erat ion of nuclear w eapons and storage of wastes.

Studies carried out at the Physics and Power Engineering Insti tute show that the problem of free plutonium can besolved by a progra m of const ruct ion of four BN-800 power unit s . Operat ing in an open version of the u ran ium -plu ton ium cycle,in 30 yr these reactors can use up the nuclear-power-grade plutonium buil t up and produced by the RT-1 plant as well as up to100 tons of weapons-grade plutonium, if necessary. This makes i t possible to reduce the buildup of 241Am appreciably and thussimpl i fy the solut ion of the ecological problems. The use of weapons-grade plutonium by conversion to nuclear-power gradeal leviates the problem of nonprol i ferat ion of nuclear weapons.

Wh en co nsidering alternative ways, one m ust bear in mind that the use of weap ons-grad e plutonium in l ight-waterreactors entails a loss of 50-60% of the power potential of plutonium for the power industry in the future. And, very important-ly, there will be an addit ional buildup of highly toxic tong-lived actinides, m ainly 241pu and 24tAm, leading to a 200-250%increase in the overall radiotoxicity of nuclear materials. When both weapons-grade and nuclear-power-grade plutonium is usedin BN-800 reactors with C R - 1, i ts energy potential is preserved and the total radiotoxicity of actinides virtually does notchange.

The use of plutoniu m in a fast reactor is com patible with actinide burning as well as the buildup o f 233U in the endbreeding zones. The in troduction of the lat ter into therma l reactors opens up new possibil i ties for enhanc ing their safety andreducing the buildup of actinides in them.

Conclusion. The high level of safety of fast reactors, the econom ic prospects, burning of actinides, and use of plutoniumare the factors that should st imulate their design and construction.

Reactor engineering has a feature that dist inguishes i t from other high-tech industries. This pertains to the dist inctiveways in which reactor engineering has developed and grown in various countries. In regard to commercial mastery of thefast-reactor technology our country is ahead of many others and, naturally, should maintain that lead.

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Proc. Intern. Conf. on Fast Reactors and Related Fuel Cycles. Kyoto, Japan, Oct. 28-Nov. 1 (1991).Yu. E. Bagdasarov, O. M. Saraev, and N. N. Oshkanov, The BN-600 Reactor. Power Unit No. 3 of the BeloyarskNuclear Power Plant, Preprint FI~I-2284 [in Russian], Physics and Power Engineering Insti tute, Obninsk (1992).L. A. Kochetkov, A. I . Kiruyushin, and N. N. Oshkanov, "Sodium-cooled fast reactors in Russia: Looking beyond theyear 2000," At. t~nerg., 74, No. 4, 282 (1993).A. A. Rineiskii , "Comparison of the technical and economic characterist ics of nuclear power plants with modern thermaland fast reactors," At. t~nerg., 53, No. 6, 360 (1982).G. Naudet, C. Satre, J. Martin, and L. Duchatelle, "The trend to the compe ti t iveness of FB R in Euro pe," in: Proc.Intern. Conf. on Fast Reactors and Related Fuel Cycles. Kyoto, Japan, Oct. 28-Nov. 1, (1991), Vol. 2, p. 18.4-1.F. M. Mitenkov and A. I . Kirushin, "Advanced commercial reactor," in: Proc. Intern. Conf. on Design and Safety ofAdva nced N uclear P ower Plants, To kyo, Japan O ct. 25-29 (1992), p. 15.6.C. Bowman, E. Artur, P. Lisowski, et al . , Nuclear Energy Generation and Waste Transmutation Using an Accelera-tor-Driven Intense The rmal N eut ron Source, Rep. LANL-UR-91-2601 (1991) .V. S. Kagramanyan, A. L. Kochetkov, and A. G. Kochetkov, "Role of fast reactors in the solution of the problems oflong-lived radioactive wastes," Book of Abstracts. Third Annu al Scientific Conferenc e of the Nucle ar Society Internation-al, Moscow, Sept. 14-18, St. Petersburg, p. 446.S. B. Bobrov, E. I . Inyutin, V. I . Matveev, et al . , "Uses of fast reactors in the USSR for radioisotopes production andminor actinides burning," in: Proc. Intern. Conf. on Fast Reactors and Related Fuel Cycles, Kyoto, Japan, Oct. 28-Nov.1(1991), Vol. 2, p. 19.4-1.V. M. Murogov, M. F. Troyanov, V. G. Ilyunin, and V. Ya. Rudneva, "A new concept of fast reactors, the potential i t iesof burning actinides and w eapon -grade pluton ium in them," in: Proc. Intern. Conf. on Design and Safety of AdvancedNuclear Power Plants, Tokyo, Japan Oct. 25-29 (1992), pp. 3-5.

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