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Prospects for Future CANDU Cycl by S.R. Hatcher This publication is a revised edition o\ a report previously published as Chapter 8 ol AECL-5800. Prospects for Future CANDU Fuel Cycles by S.R. Hatcher

Dr. Hatcher is currently Vice-President and General Manager at the Whiteshell Nuclear Research Establishment of AECL at Pinawa, Manitoba. He is a chemical engineer with over 20 years' experience in the nuclear field.

February 1979 AECL-6334 Although is a large source of in Bien que I'uranium soit une grande source d'energie , it is a finite source; and while uranium ex- au Canada, c'est une source limitee et bien que la ploration has only been renewed in earnest during the prospection de I'uranium n'ait ete reprise serieuso- past few years (and important new discoveries are be- ment qu'au cours des reventes annees (et de ing made) it is not difficult to envisage a future, 30 to nouvelles decouvertes importantes ont ete faites), on 50 years away, when uranium may be in short supply. peut envisager que dans les 30 ou 50 prochaines Fortunately, the CANDU reactor has such high neu- annees, I'uranium pourrait se rarefier. Heureusement, tron efficiency and is so flexible in its use of nuclear le reacteur CANDU a une telle efficacite neutronique fuel, that it can be adapted to advanced fuel cycles, et son combustible a une telle souplesse d'emploi employing other fissile or fertile materials, practically qu'il peut etre adapte a des cycles de combustible without modification or even interruption of schedule. avances employant d'autres matieres fissiles et fer- The prospects for future CANDU fuel cycles are re- tiles, pratiquement sans modification et meme sans viewed. interruption de service. Les possibilites des futurs cycles de combustible pour les reacteurs CANDU sont passees en revue. uranium-235 concentration from the natural 0.7 percent INTRODUCTION to about 3 per cent. CANDU fuel is made from oxide 12 Production of electricity from nuclear generating sta- which is formed into pellets '. The pellets are loaded in- tions is already a commercial reality in Canada. About to tubes of a and the ends are welded to 4500 megawatts (MW(e)) of electric capacity are in produce elements in which the uranium is completely operation. A further 10 500 MW(e) are under construc- sealed. Several of these elements are then assembled tion which will bring the total nuclear capacity to ap- to form a fuel bundle about 10 cm in diameter, 50 cm proximately 15 000 MW(e) by the late 1980's. This may long and containing about 20 kg of uranium. rise to about 60 000 MW(e) by the year 2000. The fuel bundles are loaded into and removed from The nuclear unit for these stations is the Canadian the reactor by fuelling machines which operate with pressurized heavy reactor, CANDU—PHW1)t. It is the reactor at full power. When removed from the reac- a pressure tube reactor, moderated and cooled by tor, the fuel bundle is visually the same as new fuel, but , and produces steam to drive a convention- it has now produced some 1 050 000 kW.h of electricity, al steam turbo-generator. Thus the reactor unit is ana- the same amount as would be produced by about 400 logous to the boiler in a coal-burning generating station. tons or 8 carloads of coal. Most of the fissile uranium-235 has been consumed. New fissile pluto- nium -239 and plutonium-241 have CANDU FUEL been produced from the uranium-238 and much of these have also been consumed to produce power. All nuclear reactors in operation or under development However, a significant amount of the plutonium is left are fission reactors — that is, they use to in the fuel and this provides a fueJ resource for use in break up fissile atoms in the fuel. This fissioning re- the future. leases large quantities of energy as heat, and more neu- trons to keep the going. At the same time URANIUM SUPPLY AND DEMAND neutrons are absorbed in fertile atoms, converting them to new fissile atoms. The only which occurs in nature is The uranium available in known Canadian deposits in the uranium uranium-235. Natural uranium con- 1977 has been estimated by Energy, Mines and tains about 0.7 per cent uranium-235, the balance being Resources Canada (EMR), and their estimates are a fertile isotope uranium-238. shown in Table 1|3). The estimates given are restricted to A unique feature of the CANDU reactor is lhat by only the principal deposits in Canada, and there is in ad- careful design and by using heavy water as the modera- dition a large potentia1 for finding uranium in unexplor- tor, the wastage of neutrons can be kept so small that ed regions of Canada. the chain reaction is maintained when natural uranium A natural uranium CANDU reactor consumes 134 is used as the fuel. All other commercial reactors must kgU per year per MW(e) when operating at 80 per cent have a higher concentration of the fissile isotope to . Thus, over a lifetime of 30 years it will achieve an economic fuel. This increased concentration consume about 4 MgU (about five tons of uranium ox- is produced in enrichment plants which raise the ide) per MW(e). The uranium policy of EMR, announced

t CANada Uranium — Pressurized Heavy Water in 1974'41, includes an objective to ensure at least a must be set aside for the life of these reactors accord- 30-year reserve of for all existing reactors ing to the EMR policy. Superimposed on Figure 1 are plus any reactors to be committed and planned for con- the 1977 EMR estimates of uranium resources and ex- struction during the next ten years. port commitments. Figure 1 shows the expected cumulative consump- We can see that the uranium reserves* identified in tion of Canadian uranium for reactors in Canada up to 1977 are sufficient to last into the beginning of the the year 2000. Also shown is the cumulative "commit- next century, even allowing for the 68 GgU (88 000 tons ment" of uranium; i.e., the amount of uranium which of uranium oxide) already contracted for export. However, in terms of commitment of uranium under the Canadian Uranium Raaoweaa and Commitments EMR policy, we will have committed about half the 1977 (1177 CMR iwaowea MihtiatM at tiawkgU) total resources by the beginning of the next century. Table 2 shows a similar analysis based on recent estimates of world uranium resources and consump- tion151. Canada's favourable position is not reflected on a world scale. Sixty per cent of all currently identified resources will have been consumed by the year 2000 and the commitment will exceed resources by a factor of about three. Thus, there is likely to be a worldv. ide demand for Canadian uranium, and a major export program would assist in our balance of payments as well as helping to provide the world with much needed energy. Clearly then it would be prudent to follow two ap- proaches which can assure an adequate supply of nuclear fuel for the foreseeable future: — the confirmation of more uranium resources through a stepped-up exploration program, — the development of new nuclear fuel cycles which make more efficient use of uranium. Uranium exploration is handled by the uranium pro- ducers and resources estimates are co-ordinated na- tionally by EMR. The prospects for discovery of major additional resources must be regarded as very favour- 1975 1M0 1966 19M 1996 2000 able. The rest of this paper deals with the second ap- proach, namely the more efficient nuclear fuel cycles.

Tabto 2 World Uranium RMOUTCM and RaqukwiMnts

taaowwaPfU) UnHriMm ta YaairtaMfOfU)

•aaanrahhr •••iiraa' titlmtlK IMltULf " •1'1"1 30 a Commit"* MiamnK Mtaatod 4 TaM Mm"

Canadian «HaOftsUt 82 107 318 m 806 86 490

• HSWhQUt 1823 1907 3331 2415 ~11S0B

Total 2014 2213 4227 2 BOD ~12O00

•MM HHi n W SMSMVWW bOMOQQ IM tftQ EMff OOfVMTtf tflftOflt* CanaMaA iwanwaf aw dawiflad on th# katJs ol prioc, worW ntoucoM an IIM taate of PM#vMy ooit.

* Reserves are usually taken to Include measured and Indicated resources only. They correspond to resources which can be recovered with reason- able certainty. Plutonium Recycle with Uranium FUEL CYCLE OPTIONS Extraction of the plutonium from irradiated fuel would give us the flexibility to use new fuel cycles which are Natural Uranium more efficient in uranium utilization. Because these cycles are more complex they are also more expensive The basic natural uranium fuel cycle is illustrated in at present, but they could become competitive as the Figure 2. This is the simplest fuel cycle since it requires price of uranium rises. no uranium enrichment, no fuel reprocessing and no Figure 3 illustrates the recycle of plutonium with fabrication of highly radioactive fuel. Uranium is mined, uranium. Plutonium is extracted from irradiated fuel in a purified, fabricated into fuel, used in a reactor and reprocessing plant, blended with natural uranium to stored as irradiated fuel after use. The fuel consump- produce a mixture containing about 0.5 per cent pluto- tion is 167 kilograms of uranium (0.2 tons of uranium ox- nium, and fabricated into new fuel. During the utiliza- ide) per megawatt-year of electricity generated. By com- tion of this recycled fuel most of the uranium-235 is con- parison, a simple "once-through" cycle in enriched light sumed along with much of the plutonium, but fresh water reactors consumes about 200 kilograms of plutonium is produced from uranium-238. This fuel is uranium per megawatt-year. The irradiated CANDU fuel then reprocessed for recovery of plutonium, which is contains about 0.3 per cent fissile plutonium which can returned to the cycle. be used later in other fuel cycles, but no credit is taken for this in current fuelling costs. The plutonium/uranium cycle in a CANDU reactor is not capable of producing as much fissile material as it Ngur«2 "Onoa-tttreugh" natural uranium consumes, ,• so it must always be "topped up" with lualeyd* natural uranium and plutonium. However, the total cy- cle gets tWice as much energy from the uranium, so overall urariium consumption is halved. We should note that two naw capabilities are required for this option: fuel reprocessing and "active" fabrication of fuel con- FlMl taining plutonium. Commercial reprocessing is now fabrication undertaken in some countries but Canada has no plans for commercial reprocessing at this time.

Thorium is a but contains no fissile Natural Spent foal isotope. Fissile material such as plutonium or uranium tostoraga uranium-235 must therefore be added to it to produce a reactor fuel. However, thorium readily absorbs neutrons

HutonkMHRiranMiaA fual oyon

Natural uranium Figure 4 Thorium fuel cyclo

-••Plutonium •

•••Uranium-233 •

Fuel Active fuel reprocessing fabrication

-• Thorium

Natural Fission products and Thorium uranium to storage

to produce an even more valuable fissile material, uranium-233. COMPARISON OF FUEL CYCLES The prospect of using thorium has long been re- cognized as a means of assuring an abundant supply of energy from the world's nuclear fuel resources161. Given a plentiful supply of cheap uranium, then clearly Recently AECL has summarized a detailed review of the the "once-through" natural uranium fuel cycle is the physics and economics of the thorium cycle in CANDU- simplest and cheapest. However, if uranium becomes PHW reactors'7'18"911101. The general conclusions of the scarce and the price rises, the other fuel cycles become work are that the basic CANDU reactor designs are economically competitive and may be required to en- satisfactory for thorium fuelling and that the cycle is ex- sure an adequate fuel supply in the long term. From the pected to become competitive as the price of uranium viewpoint of resource utilization, a figure of merit is the rises. amount of natural uranium consumed per unit of energy The cycle, initiated by plutonium, is illustrated in produced. Table 3 gives typical values for the fuel Figure 4. Plutonium extracted from natural uranium fuel cycles discussed and compares these with figures for can be blended with thorium to produce a mixture con- some other reactor systems and fuel cycles. Figures taining about 2.5 per cent plutonium, which is shown for thorium cycles in CANDU reactors include fabricated into fuel. Some of this plutonium is consum- the extremes between the simplest plutonium/thorium ed during the subsequent use in the reactor and cycle and what might be achieved at a slightly higher uranium-233 is produced from the thorium. The ir- fuelling cost if the system can be made self-sufficient. radiated fuel is reprocessed to recover the uranium-233 A serf-sufficient cycle would require the plutonium from and residual plutonium, which are recycled to the only 1.9 megagrams of uranium (2.5 tons of uranium ox- fabrication plant to produce new fuel. ide) for each MW(e) to start up the reactor; after that, no The recovered thorium contains some highly radio- further uranium would be required. In a slow-growth active isotopes. After a suitable period for radioactive situation the supply of this plutonium represents no decay (10 to 20 years) the thorium can be recycled. In problem, but in a rapid-growth situation there would be some fuel cycles with an appropriate reactor design it a need for additional natural uranium reactors or enrich- may be possible to maintain the cycle without further ment plants to provide the fissile material for the new addition of plutonium; in others, some "topping up" thorium reactors. would be required using new plutonium produced from Of the systems shown, only two are in commercial natural uranium. In any event, the total quantity of use today — the natural uranium CANDU and the uranium required can be reduced by a factor of at least Light Water Reactor (LWR). Uranium four, and, since the thorium is recycled, the long-term recycle and the plutonium/uranium cycles are under demand for it is quite small. development as the next phase for LWRs; the Liquid Metal Fast (LMFBR) and its fuel cycle cular interest is the fact that a 30-year accumulation of are being developed by several countries for commer- spent fuel (4130 MgU) from a 1000 MW(e) natural ura- cial use towards the end of the century. nium fuelled CANDU reactor could provide sufficient fissile plutonium to start up and operate 1400 MW(e) Tabte3 AppraxiiMt* •quWbrtum ftwl coMtimpHonO) capacity for 30 years on a high thorium cycle. Alternatively, it could oe used to start up 2200 MW(e) FIMI oontumpMon capacity to operate indefinitely on the self-sufficient flcg/MWyar) thorium cycle, at a higher fuel cycle cost due to the lower burnup and more frequent recycling. Thus the Uranium Thorium stocks of irradiated natural uranium in retrievable storage offer excellent fuel cycle flexibility for the CAMXJ •-. Natural uranium onoa-through 167 CANDU system. 1.2% Enrichad AECL has evaluated some of the basic information uranium once-through 118 and development requirements in some detail and has Plutonium/uranium 70 - outlined the fuel recycle development program which 17 81191001 Plutonium/thorium 45 1 would be required " . It would involve development Uranlum-236rthorium 32 1 of thorium and fuel fabrication methods, repro- Thorium Mlf-sufflcient — 2 cessing, demonstration of fuel management techni- ques and physics characteristics in existing CANDU LWR* Enrictfed uranium onca-through 200 reactors and demonstration of technology in health, safety, environmental, security and economics aspects Uranium rscycla 170 — of fuel recycle. The program would have to provide all Plutonium/uranium racycle 125 the necessary information for a decision on commercial scale implementation of fuel recycle. It would require 20 LMFBR* * Piutonlum/uranlum 2 — to 25 years for execution, which is compatible with the Light water r«»ctor fuelled with enricrwd uranium. present Canadian uranium resources situation. LIQUW rrwtal fait brMdar ra«ctorfuatte d with plulonlum Meanwhile AECL and other Canadian departments and urahium-238. and agencies are participating actively in the Interna- tional Evaluation (INFCE) to study methods by which the proliferation of nuclear weapons THE CANADIAN DEVELOPMENT PROGRAM can be impeded without jeopardizing the role that can play as a secure source of energy worldwide. No decisions on expansion of the present A unique feature of the CANDU system is that it can be research level on thorium fuels will be taken until infor- developed in an evolutionary way to accommodate mation from INFCE has been evaluated by the Cana- these new fuel cycles as the economic situation dic- dian Government. tates. By contrast, those countries which adopted LWRs for their first-generation nuclear program are now looking to a radically different system in the LMFBRs to CONCLUSIONS achieve efficient fuel utilization in the long term. AECL has planned a long-range recycle fuel devel- Natural uranium is the current reference fuel for the opment program to increase the utilization of our Canadian nuclear power program and will remain so for nuclear fuel resources in CANDU reactors. Its objective several decades. Present estimates of Canada's would be to develop and demonstrate a Canadian capa- uranium reserves show that there will be adequate bility in the use of uranium and thorium fuels containing uranium to meet domestic consumption and some ex- recycled plutonium and uranium-233. The particular ad- port into the next century. However, by the EMR vantage for Canada lies in the fact that the thorium cy- uranium policy standards, Canada will have committed cle could be used directly in the existing concept of a large fraction of the 1977 total resources by the end of CANDU reactor with little or no modification. No new this century. major reactor development program is required. If the Thus for the long term we need a dual program of thorium fuel cycle were in place, the existing licensing uranium exploration and development of new thorium process, reactor construction industry and utility opera- fuel cycles which give much better uranium utilization. tional structure could move gradually and smoothly into Such a dual program can be completed within the time thorium fuelling as economics and resource strategy scale required. dictated. The timing for large-scale use of the new fuel cycles Thorium fuelling could be initiated using either will depend upon how much additional uranium is uranium-235 or plutonium as fissile material. Of parti- discovered and how much we export. (10) J. Veeder, Thorium Fuel Cycles in CANDU, Pro- REFERENCES ceedings of the Second Pacific Basin Con- ference on Construction, Operation and Development. Transactions ANS, Volume 29, p.267 (September 1978). (1) CANDU 600 Station Design, Atomic Energy of Canada Limited, Report PP-28 (May 1976). J.S. Foster and S.H. Russell, CANDU-Canadian Experience and Expectations with the Heavy- Water Reactor, a review of the CANDU-PHW sys- tem. Atomic Energy of Canada Limited, Report AECL-5707 (May 1977).

(2) R.D. Page, Canadian Power Reactor Fuel, Atomic Energy of Canada Limited, Report AECL-5609 (March 1976).

(3) 1977 Assessment of Canada's Uranium Supply and Demand, Energy, Mines and Resources Canada, Report EP 78-3 (June 1978).

(4) Statement made by Minister of Energy, Mines and Resources (September 5, 1974).

(5) M.F. Duret, G.J. Phillips, J.I. Veeder, W.A. Wolfe and R.M. Williams, The Contribution of Nuclear Power to World Energy Supply, 19/5-2020, prepared for the Conservation Commission of the 10th World Energy Conference in Istanbul (Sep- tember 1977).

(6) W.B. Lewis, How Much of the Rocks and Oceans for Power? Exploiting the Uranium-Thorium Fis- sion Cycle, Atomic Energy of Canada Limited, Report AECL-1916 (1964).

(7) S.R. Hatcher, S. Banerjee, A.D. Lane, H. Tamm and J.I. Veeder, Thorium Cycle in Heavy Water Moderated Pressure Tube (CANDU) Reactors, ANS Winter Meeting, San Francisco, 16-21 No- vember 1975. Atomic Energy of Canada Limited. Report AECL-5398 (1976).

(8) E. Critoph, S. Banerjee, F.W. Barclay, D. Hamel, M.S. Milgram and J.I. Veeder, Prospects of Self- Sufficient Equilibrium Thorium Cycle in CANDU Reactors, ANS Winter Meeting, San Francisco, 16-21 November 1975. Atomic Energy of Canada Limited, Report AECL-5501 (1976).

(9) E. Critoph, The Thorium Fuel Cycle in Water- Moderated Reactor Systems. Paper IAEA- CN-36/177 presented at the IAEA International Conference on Nuclear Power and its Fuel Cycle, Salzburg, Austria, 2-13 May 1977. Atomic Energy of Canada Limited, Report AECL-5705 (1977). Copies of this publication are available from:

Atomic Energy of Canada Limited Public Affairs Office Sheridan Park Research Community Mississauga, L5K 1B2 Atomic Energy L'Energie Atomique of Canada Limited du Canada, Limited

AECL-6334 February 1979

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