Fuel Cycle of Reactor SVBR-100

Transcription

1 Proceedings of Global 2009 Paris, France, September 6-11, 2009 Paper 9236 Fuel Cycle of Reactor SVBR-100 A.V. Zrodnikov, G.I. Toshinsky, O.G. Komlev, K.G. Melnikov, N.N. Novikova FSUE State Scientific Center of Russian Federation - Institute for Physics and Power Engineering 1, Bondarenko sq., Obninsk, Kaluga rg., , Russia Tel: 7(48439)98535, Fax: 7(48439)68225, toshinsky@ippe.ru I. INTRODUCTION The design of reactor SVBR-100 allows it to operate using different types of fuel and in different fuel cycles without changing the design and deteriorating safety characteristics [1]. Fuel-at-once refueling adopted in the design (lack of partial refuelings) makes it possible to change the core content at each refueling by using the type of fuel that is the most economically effective at a current stage of nuclear power (NP) development. In the nearest future use of mastered oxide uranium fuel and operating in the opened fuel cycle with postponed reprocessing will be the most economically effective. Changeover to the mixed uranium-plutonium fuel and closed nuclear fuel cycle (NFC) will be economically effective in an event of increase of natural uranium costs when the expenditures for construction of the enterprises on reprocessing the spent nuclear fuel (SNF), refabrication of new fuel with plutonium, their operating and burial of long-lived radioactive waste are less than the corresponding costs of natural uranium, its enrichment costs, the costs of manufacturing the fresh uranium fuel and long temporary storage of the SNF. At this, it is possible to use both MOX fuel with weapon or reactor plutonium and mixed nitride fuel in case its application is more profitable. As fast reactors (FR) using uranium fuel and operating in the opened NFC consume much more natural uranium in comparison with thermal reactors (TR), and at the expected high paces of NP development the cheap resources of natural uranium will be exhausted prior to the middle of the century that will cause increase in the uranium cost, the period of FRs operating in the opened NFC must be maximally reduced. However, it should be mentioned that it is difficult to forecast reliably the date when because of the increased cost of natural uranium the NP will lose its competitiveness with electric power using fossil fuel. This is conditioned by the fact that the cost of electricity produced by the NPP is less sensitive to the cost of natural uranium in contrast to the cost of electricity produced by thermal power plants using fossil fuel. At the same time, the available resources of natural uranium are increasing progressively with increase of its cost. The expenditure caused by changeover to the closed NFC will be less, if plutonium extracted from the own SNF of uranium loads of FRs is used in fabrication of the first MOX fuel loads. If the oxide uranium fuel is used, by the end of the lifetime a comparatively high core breeding ratio (CBR) ( 0.84) of reactor SVBR-100 provides a sufficiently high content of plutonium in the SNF that may be used in the next fuel lifetimes when organizing the closed fuel cycle. Moreover, the own SNF of starting loads from oxide uranium fuel contains large quantity of unburned uranium-235 that is expedient to use for forming the load for the next lifetime. From the very beginning of realization of the extended program on implementation of reactors SVBR-100 in the NP, use of plutonium extracted from the TRs SNF for forming the starting loads of those reactors for the purpose of total elimination of natural uranium consumption will be more expensive as compared with the considered variant of changeover from the opened NFC to the closed NFC. This is conditioned by the fact that for the plutonium extracted from the TRs SNF, the plutonium cost determined by a volume of SNF reprocessing per ton of plutonium will be several times higher as compared with its cost in case of using the own SNF because of considerably less content of plutonium in the TRs SNF. It should be taken into account that the organization of the enterprise on large-scale reprocessing of TRs SNF and MOX fuel fabrication must precede the construction of NPPs with FRs. Thus, the demands in investments increase. Corresponding author s toshinsky@ippe.ru

2 At the same time, for the proposed changeover from the opened NFC to the closed one the construction of the closed NFC enterprise may be long postponed from FR launching that reduces the investment demands. At this, as the assessments have revealed, the investment fund for construction of such enterprise could be formed during about two years by including the corresponding component into the operating cost of electricity after ending the payback period of the NPP at keeping the profitableness at the same level. That approach to organization of fuel cycles with full reprocessing of the own SNF will reduce considerably the integral consumption of natural uranium, and thus it will make the NPPs based on reactor installations (RI) of the SVBR type quite competitive with the NPPs based on TRs RIs. In the closed NFC the TRs SNF (both that of WWER and RBMK) can be used (utilized) as make-up fuel, instead of waste pile uranium without separation of uranium, plutonium, minor actinides (MA) and fission products (FP). According to the ecological and economical considerations, the most expedient can be use of the dry pyro-electro-chemical methods of SNF reprocessing in chloride melts and vibro-technology for re-fabrication of fresh fuel [2]. It is presumed that storage of SNF prior to its reprocessing is realized as follows. After the spent fuel sub-assembly (FSA) has been extracted from the reactor, it is installed in a penal, where lead has been previously heated in an electric furnace over its melting point. Then the penal is sealed and transported to the dry SNF storage with natural convection air-cooling. At this, lead in the penal is solidifying gradually and forming an additional shielding barrier. Thus, the in-depth protection is provided on the way of radioactivity release out of the stored SNF. II. THE INITIAL DATA, STRATEGY AND RESULTS OF COMPUTATIONS OF CHARACTERISTICS OF CHANGEOVER TO THE CLOSED FUEL CYCLE WITH USE OF THE OWN SNF Reactor SVBR-100 is a lead-bismuth cooled fast reactor [1]. Thermal power of the reactor is 280 MW that is equivalent to electric power of ~ 100 MWe. Lifetime duration is full power hours. The height of the core is 900 mm, the core diameter is 1643 mm. In the present paper the oxide pellet fuel with averaged uranium enrichment being 16 %, with effective density being 9.65 g/cm 3 is considered for the first loads. At this, the total load over heavy atoms (h. a.) is ~9 t. The following scheme of changeover to the closed fuel cycle that allows to minimize consumption of natural uranium and only use the own SNF for fabrication of fuel for the next loads is considered. The enriched uranium oxide is loaded into the reactor at the first and second lifetimes. The third lifetime fuel load is formed from the first lifetime SNF during the second lifetime (~ 7 years), when the SNF has been cooled in a storage and reprocessed, namely: FP have been removed, built up plutonium has been separated together with MA (neptunium, americium and curium). Compensation for the mass of heavy atoms for required loading is realized by adding the enriched uranium oxide. So, the new fuel load for the third lifetime is a mixture of three components: 1 - extracted plutonium along with MA built up during the first lifetime, the total mass is ~370 kg (h. a.); 2 - extracted uranium, the total mass is ~8019 kg (h. 235 a.) and enriched in U by 10.8 %; 3 - added enriched uranium oxide, the total mass is ~715 kg (h. a.). Component 2 is distributed uniformly over the core. Shaping of power distribution could be realized by non-uniform distribution of plutonium over the core zones or use of various enrichment of added uranium oxide in each zone. Similarly, the forth lifetime loading is formed from the second lifetime SNF, the fifth lifetime loading is formed from the third lifetime SNF and so on. The neutron-physical characteristics of the cores during the lifetime process were calculated in a system of 26-group diffusion approximation in two-dimensional cylindrical R-Z geometry with use of code complex REACTOR [3] with a system of constants BNAB-93 [4]. The computation model of the reactor is presented in Fig. 1. Fuel loading was determined from the necessary burn-up reactivity margin for providing the required lifetime duration without account of the temperature effect, flattening of power distribution was realized with the help of four physical shaping zones. The computations have revealed that by varying the enrichments of added uranium oxide (component 3) at uniform distribution of the old uranium (component 2), it is impossible to flatten the power distribution in the reactor to the acceptable value of the radial peaking power factor K r that is integral over the core height. On the basis of experience of designing the fast reactors with Pb-Bi coolant, this coefficient must be less than For that reason, in all next computations physical shaping of power distribution is realized by non-uniform distribution of plutonium oxide PuO 2 (component 1) over the zones: its content is increasing from a center to periphery. Enrichment of the added uranium oxide is the same for all zones.

3 Z, cm R, cm Fig. 1. The computation model of the reactor (the figures designate the following physical zones: 1, 2, 3, 4 - fuel physical shaping zones+ steel + Pb-Bi; 5, 8 - FSA structure elements steel + Pb-Bi; 6 - bottom reflector steel + Pb-Bi; 7 - plenum for collecting the gas FP + steel + Pb-Bi; 9 - side reflector steel; 10 - radiation shield boron carbide.) The results of computation of neutron-physical characteristics of the core for the certain lifetimes with mixed fuel are summarized in Table I. The obtained change of reactivity for each calculated lifetime is shown in Fig. 2. The quantity of consumed natural uranium G natural cited in Table 1 is calculated with the help of formula: enriched waste (x5 x5 ) Gnatural = Genriched (1), natural waste (x5 x5 ) where, G the required quantity of enriched uranium, enriched natural 5 Table I Characteristics of the Core for the Different Lifetimes x = 0.7% the content of U in natural uranium, waste 235 x 5 = 0.2% the content of U in waste pile uranium, enriched 235 x 5 the content of U in the added enriched uranium. Lifetime number 1, 2 3, 4 5, 6 7, 8 9, 10 11, 12 13, 14 15, 16 Enrichment of added UO2, % 15.9 * Added 235 U, kg Added 238 U, kg Total quantity of 235 U, kg Used natural uranium, t Total quantity of Pu (all isotopes), kg Distribution of built up shaping zones, kg Pu over the Zone 1 Zone 2 Zone 3 Zone Maximal K r Maximal change of reactivity swing during max min Кeff Кeff the lifetime, % max min Кeff Кeff Breeding ratio * Note: fuel enrichment averaged over the core is given for the first and second lifetimes

4 0.06 Reactivity margin, (Keff 1)/Keff фф фф Номер Lifetime кампании: number: I,II III, IV V, VI VII, VIII IX, X XI, XII XIII, XIV XV, XVI Full power hours Fig. 2. Change of reactivity margin during the lifetime The corresponding diagram of the integral and annual uranium consumption in terms of 1 GWe are presented in Fig. 3 and Fig. 4. For comparison, a similar dependence for reactor WWER-1000 is presented too. The latter dependence is obtained for initial uranium loading of 65 t with averaged 2.9 % enrichment and annual 22 t consumption of 4.4 % enriched uranium [5]. The content of different isotopes in fuel loads and different lifetimes SNF are presented in Table II.

5 Isotope Table II. The content (kg) of major isotopes of heavy atoms in the SNF after cooling in the storage during 7 years Lifetime number 1, 2 3, 4 5, 6 7, 8 9, 10 11, 12 13, 14 15, 16 U U U U Pu Pu Pu Pu Pu Np Am Fission products Curium 6.7E E E E E E E E-01 Others <0.1 < The quantity of used natural uranium, thousand tons СВБР-75/100 SVBR WWER-1000 ВВЭР Time, years Fig. 3. Integral consumption of natural uranium at power of 1 GWe

6 Fig. 4. Annual consumption of natural uranium (in comparison) III. THE INITIAL DATA, STRATEGY AND RESULTS OF COMPUTATIONS OF CHARACTERISTICS OF CHANGEOVER TO THE CLOSED FUEL CYCLE WITH MAKE UP OF THERMAL REACTORS SNF To evaluate the characteristics of changeover to the closed fuel cycle with make up of TRs SNF, the thermal power of the reactor is adopted to be 280 MW, lifetime duration Т 10 years at loading factor being 0.85 (Т = full power hours). The vibro-packed МОХ fuel with inclusion of transuranium elements (TRU) plutonium and MA with effective density 9,7 g/cm 3 and addition of depleted metal uranium ( 10 % by weight) [2] was used as fuel composition. To flatten the power distribution, physical shaping of power distribution along the core radius is used by changing the TRU content in МОХ fuel. From 4 to 6 groups of fuel elements with different content of TRU, which increases from the core center to the periphery, is used. Power distribution is characterized by a value of radial peaking power factor K r max that is integral over the core height. In all computations, which results are described below, K r max 1.25 during the current lifetime. To changeover to the closed fuel cycle, the following scheme is adopted: a reactor loaded with UO 2 is operating during several lifetimes, duration of each one is full power hours, in order to build up the TRU, which amount is enough for loading the core by МОХ fuel; further this operating stage is considered as a zero lifetime; after that the reactor is operating in a closed cycle mode with lifetime duration being full power hours. when МОХ fuel for the first loading is manufactured, instead of UO 2 with depleted uranium, TRs SNF is used. It was mentioned above that with the help of preliminary thermo-chemical processing, gas and volatile FP were eliminated from TRs SNF similarly to the DUPIC technology for reactors CANDU [6]; in all next lifetimes MOX fuel is manufactured from own SNF of reactor SVBR-100 (hereinafter SVBR SNF) freed from FP. The TRs SNF is used as make up fuel; it is adopted that the amount of make up fuel equals to that of the FP removed from the SVBR SNF, which, in its turn, is composed from the FP contained in the TRs SNF and built up during the current lifetime SVBR-100. If the amount of TRU extracted from the reactor (with due account of required cooling) is enough to fabricate MOX fuel loading for the next lifetime, which duration is full power hours, reactor SVBR-100 can operate in

7 a closed fuel cycle with TRU self-providing and utilizing of the certain amount of TRs SNF. The computations of the first 7 lifetimes were performed in the described above mode. The SNF of reactor WWER-1000 (hereinafter WWER SNF) or SNF of reactor RBMK (hereinafter RBMK SNF) was used as make up fuel. The isotopic content of TRs SNF is adopted in accordance with [7] for a 15-year cooling period. When forming a calculated isotopic content, Kr, Xe, I, Cs were removed from the TRs SNF. The RBMK SNF contains less amount of FP and, correspondingly, more amount of 238 U. As for the rest, the isotopic contents are almost the like. The computations have revealed that for the first MOX fuel loading with WWER SNF make up, 4 zero lifetimes of the reactor fueled with UO 2 is required, and with RBMK SNF make up, the required quantity of the SVBR TRU has been built up for 3 zero lifetimes. Change of К eff during the lifetime process for the first 7 lifetimes for the variant with WWER SNF make up is presented in Fig. 5. For comparison, the corresponding dependence for the reactor with oxide uranium fuel is presented in Fig. 5 too. When RBMK SNF make up is used, behavior of К eff (t) is similar to that shown in Fig. 5. The quantity of the TRs SNF utilized per 1 GWe in the considered cycle in the mentioned lifetimes of SVBR-100 is shown in Fig. 6. The presented results reveal that for the 7 lifetimes К eff (t) is approaching a certain steady function. KК eff эфф 1,06 1,05 1,04 1,03 СВБР-UO2 SVBR 2 1-я 1 st lifetime кампания 2-я 2 nd lifetime кампания 3-я 3 rd lifetime кампания 4-я 4 th lifetime кампания 5-я 5 th lifetime кампания 6-я 6 th lifetime кампания 7-я 7 th lifetime кампания 1,02 1,01 1, Time, thousand время, full тыс. power эфф. hours часов Fig. 5. К eff (t) dependences for different lifetimes when WWER SNF make up is used

8 TRs' SNF amount, tn Lifetime number WWER SNF RBMK SNF Fig. 6. The integral amount of TRs SNF utilized per 1 GWe as a function of SVBR-100 lifetime number. On the whole, on the basis of the performed computations we can say that reactor SVBR-100 can operate in a closed fuel cycle and use plutonium extracted from the own SNF for manufacturing MOX fuel and utilize as make up fuel the TRs SNF that has been only subjected to thermo-chemical processing with removal of gas and volatile FP. IV. CONCLUSIONS special fuel and fuel cycle, which are different from those used in large NP. Adaptability of the SVBR-100 reactor relative to the fuel type and fuel cycle makes it possible to realize a timely and gradual changeover to the closed NFC that will be economically justified. Simultaneously, the problems of utilization and radiation-equivalent burial of long-lived radioactive waste will be solved, keeping in mind that minor actinides are effectively burned in the FR. The performed computations have revealed, that changeover to the closed NFC for FR SVBR-100 with use of plutonium extracted from the own SNF can be realized at the third lifetime i.e. in 16 years. During the 60 years of the RI service lifetime, the consumption of natural uranium calculated for 1 GWe will be by 40 % less than its consumption by reactor WWER-1000 for the same time. The principal opportunity to utilize the TRs SNF as make-up fuel when RI SVBR-100 is operating in a closed fuel cycle has been shown. Of course, during a long process of changeover to complete closing of the NFC by recycling the plutonium and MA, the economically expedience may be the stage with incomplete closing of the NFC, in which uranium recycling is only organized and plutonium and MA recycling is postponed till a considerable number of FRs is implemented in the NP. As, first of all, reactors SVBR-100 are intended for use in regional and small power, they do not need the CBR FP FR FSA MA MOX fuel NFC NP NPP RBMK RI SNF SVBR TR TRU WWER NOMENCLATURE core breeding ratio fission products fast reactor fuel sub-assembly minor actinides mixed oxide fuel nuclear fuel cycle nuclear power nuclear power plant channel large power reactor reactor installation spent nuclear fuel lead-bismuth cooled fast reactor thermal reactor transuranium elements water-cooled water-moderated power reactor

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