Atomic Energy, Vol. 89, No. 4, 2000
NUCLEAR FUEL FOR WATER-COOLED POWER REACTORS. STATUS AND PROSPECTS
V. F. Konovalov,1 V. L. Molchanov,1 M. I. Solonin,2 Yu. K. Bibilashvili,2 and V. A. Tsykanov3
Investigations performed in the last few years have made it possible to ensure reliable and safe operation of VVÉR reactors in three- and four-year fuel cycles with average burnup 43–45 NW·days/kg U (complete with off loaded fuel assemblies). Specifically, prototype operation of fuel in a 5-yr cycle is now being conducted on individual power VVÉR-440 power-generating units (No. 4 Kola and No. 2 Roven). VVÉR reactors can be divided into four groups according to the conditions of fuel operation and the level of and reasons for failures of fuel elements: VVÉR-440 of the type V-230, V-179, and V-270 – the first generation of reactors; VVÉR-440 of the type V-213 – second improved generation of reactors, VVÉR-1000 (V-187 type, the only unit at the Novovoronezh nuclear power plant, the fuel assemblies of this reactor have a hexagonal jacket), and serially produced VVÉR-1000 in which the fuel assemblies are unjacketed. In VVÉR-440, just as in all VVÉR-1000, the structural and technological solutions with respect to fuel elements and fuel assemblies are unified to a high degree. Nonetheless, failures of fuel elements are of a random character in the V-213 type VVÉR-440 and in all VVÉR-1000. In the last several years the level of fuel-element failures in these reactors is on the average ~(2–3)·10–5 (VVÉR-1000) and ~(3–5)·10–6 (VVÉR-440 of the type V-213); this corresponds to the modern indicators of the leading western fuel suppliers. The failure level in type V-230 VVÉR-440 is appreciably higher (Tables 1 and 2). This has become especially noticeable in the last 5–7 yr (aging of the reactors). Post-reactor investigations of the fuel assemblies in the third unit of the Novovoronezh nuclear power plant (V-230) showed that fuel elements most likely fail because of high vibrational loads on fuel assemblies. Even though the operating indicators of the cores are good, VVÉR are still not as good as their western analogs with respect to the economic indicators. The main reasons why the economic indicators of the serial VVÉR, and primarily VVÉR-1000, are not as good as their western analogs are as follows: – use of stainless steel as a structural material for the spacing lattices and the guiding channels (about 2 tons in the VVÉR-1000 core); – use of consumable absorbing rods (VVÉR-1000) or fuel compensators (VVÉR-440) in the core to compensate excess reactivity, in contrast to neutron absorber, used in most PWR, in the fuel; – substantial neutron leakage as a result of a suboptimal fuel reloading scheme; – use of zirconium alloys with high hafnium content. Consequently, further improvement of the structural and technological solutions with respect to fuel elements in fuel assemblies and with respect to the core as a whole has an important place in the work to improve the economics of the VVÉR fuel cycles at the modern level. 1
Open Joint-Stock Company “TVÉL.” State Science Center of the Russian Federation – A. A. Bochvar All-Russia Scientific-Research Institute of Standardization in Machine Engineering. 3 State Science Center of the Russian Federation – Scientific-Research Institute of Nuclear Reactors. 2
Translated from Atomnaya Énergiya, Vol. 89, No. 4, pp. 325–334, October, 2000.
1063-4258/00/8904-0843$25.00 ©2000 Plenum Publishing Corporation
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TABLE 1. Operation of Fuel Assemblies in VVÉR-400 Year
Number of off-loaded
Number with leaks
Fraction of leaking
V-213 1998
1676
0
0
1999
998
5
~4·105
1998
747
79
8·10–4
1999
453
39
6.8·10–4
V-230
The departmental program, which is being conducted at the present time in the country, “fuel elements and fuel assemblies of nuclear reactors in nuclear power plants” for developing improved fuel cycles and a new-generation fuel presupposes that the following characteristics will be attained in the VVÉR core in the near future (2000–2003): – maximum fuel burnup in a fuel assembly up to 55 MW·days/kg U (4-yr fuel cycle in VVÉR-1000 and 5-yr cycle in VVÉR-440). For comparison, at the present time the serially delivered and licensed product of the western firms (Framatom, Siemens) for PWR has a maximum design burnup of 52 MW·days/kg U; – support for maneuvering characteristics of the nuclear power plant; – transition to reloading fuel using the in-in-out scheme; – increase in the duration of a fuel run up to 350 effective days; – fuel assemblies that can be disassembled; – use of zirconium alloys with hafnium content no greater than 0.01 mass% as a structural material for the spacing lattices, guiding channels, and fuel assembly jackets; – use of neutron absorber (UO2–Gd2O3); – use of fuel pellets with optimized parameters with respect to microstructure, physicochemical characteristics; – adding recovered uranium to the fuel cycle; – use of zirconium alloy É-635, which has a high radiation and corrosion resistance, as the structural material for fuel element cladding, pipes of the guiding channels, and the spacing lattices; – increase of the operational reliability of fuel up to a level of less than 10–5 failures (for the off-loaded fuel assemblies). The adoption of a new fuel in VVÉR will make it possible to increase substantially the economic indicators of fuel cycles and safety. At the same time, natural uranium will be consumed at the current level ~0.196 kg/(MW·day). The new-generation nuclear fuel has been under development for VVÉR-1000 since the beginning of the 1990s. The first test batch of improved fuel assemblies with guiding channels and spacing lattices made of the zirconium alloy É-110 instead of stainless steel was installed in the No. 1 unit of the Balakov nuclear power plant (base unit for testing new or improved fuel) in 1993. In 1994 the first test batch of fuel assemblies with uranium-gadolinium fuel was installed in the No. 3 unit of the Balakov nuclear power plant. In the same years two circumstances influenced the delay and development of work on the commercial adoption and licensing of improved nuclear fuel and fuel cycles for VVÉR-1000: – curving of fuel assemblies and the core as a whole because of axial “overcompression” of the fuel assemblies by intravessel devices in the reactor (the result of incorrect control assembly of intravessel devices during the mounting work); – increase in the testing time for the experimental batches of improved fuel assemblies from 3 to 5 yr because of dispatcher limitations at the Balakov nuclear power plant. Fuel assemblies with uranium–gadolinium fuel are now in prototype operation in all four units of the Balakov nuclear power plant: in units Nos. 2, 3, and 4 they are operating within one fuel reloading (48 improved fuel assemblies instead of 54 serial assemblies), and at the No. 1 unit the core will be completely formed from such fuel assemblies during the planned maintenance. A commercial technology for fabricating uranium–gadolinium fuel pellets has been assimilated and adopted at the Ust’-Kamenogorsk plant. The same technology is also being adopted at the plant in Élektrostal’. The technology for fabricating uranium–gadolinium fuel was mastered and adopted with direct participation of the staff of the Bochvar Institute. 844
TABLE 2. Operation of Fuel Assemblies in VVÉR-1000 Parameter
Number of off-loaded (for all units)
Value
1798
Number with leaks according to the KGO method: new*
18
old
53
Average level of damage to fuel elements (ratio of the number of leaking elements to the total number off-loaded):
*
Nuclear plants in Russia
2.5·10–5
Nuclear power plant in Ukraine
6.8·10–5
According to the old norms, fuel assemblies whose activity in the KGO1 container
exceeds the background by 3σ were considered to be leaking. According to the new norms, besides the indicated condition, the activity of the fuel assemblies must exceed 1·10–6 Ci/kg. 1
TRANSLATOR’S NOTE: KGO is the Russian acronym for “Monitoring of the seal of the
cladding of fuel elements.”
Thus, the scientific-technical and technological experience permits commercial adoption of the 4-yr fuel cycle based on improved fuel assemblies with uranium-gadolinium fuel in 2001 (first step – makeup volume in the stationary state 48 fuel assemblies). The technical-economic investigations have shown that when the 4-yr fuel cycle is adopted (stage 1) the economic effect from a decrease of the cost of the makeup fuel, elimination of rods with a consumable absorber from the core, a decrease in the storage costs, and removal of spent fuel is equivalent to approximately 12 fuel assemblies per reactor per year as compared with the design 3-yr cycle. Work on adopting fuel assemblies with uranium-gadolinium fuel at the Balakov nuclear power plant permitted making a substantiated decision about supplying improved fuel at the Rostov nuclear power plant, beginning with the first fuel load, using improved fuel and with the stationary state reached in the 4-yr cycle. Another problem appeared when the zirconium spacing lattices were introduced in 1998 – the lattices shifted relative to the initial position (Balakov, Zaporozh’e, and Roven nuclear power plants). The shift was due to work omitted by the builder on the improved fuel assemblies. This deficiency was eliminated in 1999. At the present time, at the initiative of the Open Joint Stock Company “TVÉL,” work on developing a new construction of fuel assemblies with a rigid framework, which will make it possible to operate the core in the 4- and 5-yr fuel cycles of VVÉR-1000, is being done on the basis of the results of operating the improved fuel assemblies and analysis of the thermomechanical investigations of the construction of unjacketed fuel assemblies. The first test batch of such fuel assemblies will be installed in 2002. The Special Office of Design and Machine Building has developed a new alternative variant of a VVÉR-1000 fuel assembly. This design is based on the use of a strong bearing framework, which provides the fuel assembly with acceptable stability against shape change. Such fuel assemblies are being tested at the Kalinin nuclear power plant (unit No. 1). At the end of June 2000 the unit was stopped for planned maintenance, during which all fuel assemblies will be examined. The state of the core of the indicated unit at this moment makes it possible to conclude that the alternative fuel assemblies operate normally (no failures). Another 60 fuel assemblies will be installed. If the test operation is successful, the fuel assemblies can be recommended for implementing 4- and 5-yr fuel cycles on unit No. 1 at the Kalinin nuclear power plant. A comparative analysis, performed by Special Office of Design and Machine Building, of the efficiency of the fuel cycles of the VVÉR-1000 core showed that the transition to the 4-yr (and longer) fuel cycle will make it possible to decrease substantially the cost of the energy generated, and a transition to an 18-month run will increase the yearly energy output of the nuclear power plant. The analysis was performed on the basis of an increased degree of burnup of the fuel to 55 MW·days/kg U.
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TABLE 3. Additional Irradiation of VVÉR-440 Fuel Elements up to Burnup 72 MW·days/kg U and VVÉR-1000 Fuel Elements up to 63 MW·days/kg U
Nuclear power plant, unit
Kola, No. 3, VVÉR-440
Novovoronezh, No. 5, VVÉR-1000
Type of fuel element
Bmax/B initial, MW·days/kg U
Bmax/ B after additional irradiation, MW·days/kg U
Qmax after additional irradiation, W/cm
PTM
61.1//52.9
72/68
207
–”–
60.6/52.3
72/68
208
RFT
60.0/51.4
72/69
239
PTM
48.8/44.6
82/57
222
–”–
49.7/45.2
63/58
231
RFT
49.0/44.6
72/72
247
TABLE 4. Intensity of the Eγ = 514 keV 85Kr γ Line in the Gas Cavity of Full-Scale VVÉR Fuel Elements Burnup, MW·days/kg U Type of fuel elements
before additional irradiation
after additional irradiation
maximum
average
maximum
average
Maximum load at the end of additional irradiation, W/cm
Intensity, counts/sec·104 before additional irradiation
after completion of additional irradiation
PTM VVÉR-1000
48.8
44.6
62
57
222
~1.1
~1.4
Same
49.7
45.2
63
58
231
~1.1
~1.7
61.1
52.9
72
68
207
~2.7
~5.4
60.6
52.3
72
68
208
~2.8
~5.5
PTM VVÉR-440 Same
The status of the work on improving the nuclear fuel for VVÉR-440 can be characterized as follows: – test operation of the nuclear fuel is continuing on unit No. 4 of the Kola power plant and unit No. 2 of the Rovno power plant in the 5-yr fuel cycle, which on the basis of the fuel use characteristic (specific consumption of natural uranium) corresponds to the best indicators of foreign PWR; – work on licensing the 4-yr fuel cycle for the “Dukovany” (Czechoslovakia), “Mokhovtse,” No. 1 unit (Slovakia) and the “Paksh” (Hungary) nuclear power plants has been completed; such fuel cycles have already been adopted at the Dukovay and Mokhovtse nuclear power plants; the improved nuclear fuel will be delivered to the “Paksh” nuclear power plant beginning in 2000; – scientific research and development work for licensing the 4-yr fuel cycle for unit No. 2 in the Mokhvtse nuclear power plant and units Nos. 3 and 4 in the Yaslovske-Bogunitse (Slovakia) nuclear power plants is being conducted. As we have already mentioned, the aging of the first-generation VVÉR-440 (types V-230, V-179, and V-270) directly affects the operational reliability of the fuel assemblies. This has made it necessary to develop an improved construction with greater vibrational stability of the fuel bundles. In 1999 such a fuel assembly was developed and a test batch was installed at the No. 3 unit of the Novovoronezh nuclear power plant, and such fuel assemblies were delivered to the “Kozlodui” nuclear power plant (Bulgaria). To increase the operational reliability of fuel assemblies and expand the reactor control algorithms (maneuvering), scientific research and development work on substantiating the construction of the ARC fuel assemblies with an improved joining unit was completed in 1999. A test batch of fuel assemblies will be installed in 2000 in the No. 4 unit of the Novovoronezh nuclear power plant. Work on developing and adopting modernized working fuel assemblies and ARC fuel assemblies in nuclear power plants is being conducted in accordance with the program, approved in “TVÉL” for modernizing VVÉR-440 fuel assemblies. The purpose of this work is to decrease coolant leakage in the interjacket space (i.e., to increase the thermal engineering reliability of the cooling of fuel elements) and to improve the water-uranium ratio. To this end the dimensions of the jackets of the 846
Fig. 1. Gas release from the fuel in the fuel elements.
working fuel assemblies have been increased to 145 mm, and up to 144.2 mm for the ARC fuel assemblies (the design value is 143 mm); the jacket thickness is decreased from 2 mm to 0.5 mm, and the spacing between the fuel elements is increased from 12.2 to 12.3 mm. The fuel load in the core is increased because of an increase in the height of the fuel column in the fuel elements by 100 mm. Optimized 5-yr fuel cycles with uranium-gadolinium fuel for VVÉR-440 (type V-213) cores are being developed on the basis of the improved working fuel assemblies and the ARC fuel assemblies. The expected fuel burnup is up to 53 MW·days/kg U. The first test batches of the improved fuel assemblies in the 5-yr cycle will be installed in 2002 in the No. 3 unit of the Kola nuclear power plant and in one of the units of the “Dukovany” nuclear power plant (Czechoslovakia). The duration of the fuel run for this plant will be 320 effective days. Experience in operating VVÉR fuel and the large amount of experimental data from post-reactor investigations in hot laboratories have shown that burnup can be further improved. This has also been confirmed by an experiment with additional irradiation of fuel elements, taken from standard spent fuel assemblies of commercial reactors, in a loop setup of the MIR research reactor (Tables 3 and 4). The investigations showed that all basic characteristics of the fuel elements (dimensions, fuel cavity, yield of gaseous fission products, degree of oxidation of the cladding on the outer and inner sides, mechanical characteristics of the cladding), obtained with burnup 50–55 MW·days/kg, can be extrapolated to a higher burnup 70–75 MW·day/kg U (Fig. 1). However, burnup is not the only factor that determines the real resource characteristics of the fuel elements of commercial reactors. Licensing of working and resource characteristics of fuel elements with increased burnup in VVÉR requires a more detailed study and analysis of the following most important questions: – accumulation of damage in the cladding of fuel elements, including taking account of the admissable technological defect, in the production of tubes, in the transitional operating regimes with determination of the admissable abrupt change in power with burnup above 50–60 MW·days/kg U; – gas release from the fuel; – corrosion of the cladding material, including in the presence of tensile stresses; – weaker securing of the fuel elements in the spacing lattices as a result of the relaxation of stresses and increase in the vibrational modes on fuel elements; – effect of LOCA type accidents and reactivity accidents on the state of fuel elements. One of the most important ways to increase the resource characteristics of fuel elements is to decrease the damage to the cladding, which appears and accumulates when tensile stresses arise in the cladding. To solve this problem uranium dioxide fuel with dopants, which, on the one hand, decrease the resistance of the fuel core to deformation and, on the other, optimize its structure, has been developed. Figure 2 shows the results of experimental investigations designed to determine the threshold stresses under which the free swelling of the fuel core can be suppressed. For a fuel core with dopants (curve 4) it is ~2.7 MPa at 380–420°C; for pure
847
Fig. 2. Rate of radiation creep versus the stress at temperature 1010 (1), 900 (2), 490 (3), 390°C (4) and Φ = (7.2–2.5)·1013 fissions·sec–1·cm–3.
Fig. 3. General results of the tests of refabricated fuel elements in the BIGR reactor.
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Fig. 4. Diagram of the destruction of cladding made of É-110 alloy.
uranium dioxide fuel it is ~8 MPa (T = 445°C) and 12 MPa (T = 350°C). Thus, the doped fuel makes it possible to decrease the accumulation of damage in the cladding and to increase fuel burnup. A new material for fuel-element claddings – zirconium alloy É-635 (Zr–Nb–Sn–Fe) – is being considered to increase fuel burnup. This material has a high radiation and corrosion resistance. The high radiation resistance of the alloy imparts geometric stability to the fuel elements and fuel assemblies throughout a long service life up to fluence ~1023 cm–2. The results of experimental investigations of the behavior of fuel elements in reactivity accidents are presented in Fig. 3. It is evident that the fuel meets the licensing criterion “absence of fuel fragmentation” up to burnup ~62 MW·days/kg U. Figure 4 shows the results of experimental works studying the state of fuel-element cladding in LOCA type accidents. It is evident that fuel burnup does not affect the licensing criteria for accidents of this type. The requirements which the fuel must meet for the maneuvering regimes of operation are now urgent for operating nuclear power plants and plants under construction, including following foreign contracts. The operating conditions of fuel elements in the regime tracking the grid load are much more stringent than in the base regime. Additional tensile stresses, capable of damaging fuel elements if a substantial number of changes occur in the reactor power during maneuvering of plant operation, appear during heat changes in the fuel-element claddings. The main mechanisms leading to damage of zirconium cladding are corrosion cracking in the presence of corrosive fission products and exhaustion of the fatique cyclic strength. The structural-technological solutions, incorporated in the modern construction of a fuel element, are largely responsible for their working capacity in the maneuvering regime. Cladding made of Zr–1%Nb alloy, showing low oxidation and hydration under irradiation, possesses high mechanical properties with respect to strength and residual plasticity. The use of fuel pellets with a central opening increases substantially the relaxational possibilities of fuel elements. The use of zirconium tubes with a smaller production defect (35 µm) increases the strength of the fuel-element cladding with respect to corrosion cracking under stress. All this produces favorable prerequisites for studying and predicting the operation of fuel elements with the modern construction in maneuvering regimes. The maneuvering characteristics of fuel are based on extensive computational–experimental investigations. A representative volume of tests of VVÉR fuel elements with an abrupt change in power up to burnup 60 MW·days/kg U was performed in the MIR reactor. The admissable threshold stresses in the fuel-element claddings, taking account of production defects, are established on the basis of extensive investigations of the strength of initial and irradiated claddings. A complex of completed and continuing investigations of the cyclic strength of initial and irradiated claddings, consisting of zirconium alloys, up to 108 cycles makes it possible to estimate the working capacity of fuel elements taking account of the accumulation of fatigue damage. Calculations of the strength of fuel elements in regimes with a change in power determine the admissable local jumps of 849
Fig. 5. Variation of the power per unit length of a VVÉR-1000 fuel element and stresses in the cladding during daily maneuvering.
the specific load in fuel elements; these jumps are the basis for development of optimal algorithms for controlling the core during power maneuvering of a nuclear power plant. The possibilities of limited maneuvering within 20% were studied for the No. 5 unit of the Zaporozh’e nuclear power plant. The Russian Science Center “Kurchatov Institute” has tested the control algorithm developed on this unit. Calculations of the working capacity of fuel elements in this regime were performed at the Bochvar Institute. Figure 5 shows the computed plots of the variation of the local power and maximum tangential stresses in the cladding of a fuel element. The local jumps in power during maneuvering (with respect to stationary values) do not exceed 30 W/cm, and the maximum tensile stresses everywhere remain below 110 MPa, which is two times less than the threshold value for the onset of corrosion cracking. Under these conditions nucleation or development of an initial defect in the cladding does not occur and the fuel elements are capable of operating reliably for the entire run in a given maneuvering regime. Testing of refabricated VVÉR-440 fuel elements in the maneuvering regime are planned in the MIR reactor in 2000. Similar tests must also be performed for VVÉR-1000 fuel elements. Completion of the substantiation and experimental operation of the No. 5 unit of the Zaporozh’e nuclear power plant in a regime with limited maneuvering (20%) would greatly facilitate the practical assimilation of load-tracking regimes. Work on further improvement of RBMK fuel is directed primarily toward increasing safety. After the Chernobyl accident the steam coefficient of reactivity of RBMK was substantially lowered as a result of additional absorbers placed in the core; this decreased the fuel burnup and also increased the average and maximum power of a fuel assembly. Consequently, this solution was judged to be suboptimal. Computational investigations directed toward lowering the steam coefficient of reactivity showed that a better solution is to use a consumable erbium absorber in the form of Er2O3 additions to the UO2 fuel pellets (~0.4–0.6 mass%). The use of uranium–erbium oxide fuel in RBMK decreases the steam coefficient of reactivity to a level at which it is no longer necessary to install additional absorbers in the core. Moreover, the uranium–erbium fuel decreases the nonuniformity of energy release, increases the fuel enrichment, and thereby increases burnup. The uranium–erbium fuel also made it possible to increase the operational reliability of fuel elements. Only nine of the 6000 fuel assemblies with uranium–erbium fuel, which were in operation (beginning in 1995) at the Leningrad and Ignalin nuclear power plants (six units) failed. In the next two years fuel assemblies with uranium–erbium fuel with optimal enrichment and erbium content will be installed; this will increase burnup. The development and adoption of fuel assemblies with centrally secured fuel elements will increase the operational reliability (the first test batch of such fuel assemblies will be installed in the Leningrad nuclear power plant). 850
The strategy of Open Joint Stock Company “TVÉL” as a supplier of nuclear fuel is to provide the maximum possible services for fuel supply to nuclear power plants. An effective scientific–technical policy in the development, licensing, and following the operation of fuel plays a central role in the solution of this strategic problem. Another important action in this direction is the formation in 1999 of the association of participants in the development of nuclear fuel “TVÉL–NAUKA,” which, together with “TVÉL,” the leading scientific and design nuclear centers in Russia also joined. The urgency today lies in the fact that the competition for the traditional, for Russia, seller’s market for nuclear fuel in foreign nuclear power plants with VVÉR is entering a new phase – the phase of installment of experimental batches of fuel assemblies by foreign suppliers. Specifically, the working VVÉR-440 fuel assemblies made by BNFL (Great Britain) are operating in the No. 2 unit of the Lovis nuclear power plant (Finland). This has enabled BNFL to sign a contract for supplying fuel for one of the units at the Lovis nuclear power plant; a test batch of working BNFL fuel assemblies with uranium–gadolinium fuel will be installed in 2003 in one of the reactors in the “Pakash” nuclear power plant (Hungary); the Westinghouse Corporation (USA) is conducting work to install in 2003 a test batch (up to six) of fuel assemblies in one of the VVÉR-1000 reactors in the southern Ukraine nuclear power plant. The competitiveness of Russian nuclear fuel under current conditions is the main direction of work in the next three to four years (short-term program). Russian nuclear fuel and fuel cycles for power reactors are based on modern engineering–physical principles of fuel design and core design (depending on the type of reactor): – maximum use of zirconium alloys in fuel assemblies; – use of a consumable absorber (gadolinium and erbium) introduced into the fuel composition; – increase of fuel burnup; – shaping of fuel over the cross section of a fuel assembly; – use of the in-in-out loading scheme; – collapsible construction of fuel assemblies, and so on. The alloy É-110, which with respect to certain important properties surpasses the main alloy used in western fuel assemblies zircolloy-4, is used as the main structural material. Work on the promising alloy É-635 is being actively conducted. The serial production of western firms for PWR differs by a somewhat higher burnup and different duration of a fuel run (12, 18, and 24 months). The design burnup of the fuel provided by Westinghouse for the Temelin nuclear power plant is 52 MW·days/kg U. The excess production capacities of western manufacturers of nuclear fuel and the requirements of operators for decreasing the fuel component of the cost of electricity produced are forcing fuel suppliers to increase the technical–economic characteristics further. The commercial-test operation of a new-generation fuel in PWR by leading western firms “Framatom” (France, AFA-3G assembly), “Siemens” (Germany), and “Westinghouse” (USA) at the present stage is characterized by the following indicators: – general trend – high operational reliability with increase in work (fuel supplier, “free of problems,” Framatom”) with failure level 1·10–6; – construction of fuel assemblies with high resistance to bending; – complete insertion of control rods into the core; – use of corrosion-resistive materials as the construction materials; – adoption of a shielding lattice consisting of auxiliary objects. Conclusions. At the present and in the next three or four years the main direction of work is to ensure competitiveness of the Russian nuclear fuel in the traditional markets of the country. The scientific-technical and technological store of knowledge make it possible to introduce in the near future into power plants with VVÉR reactors fuel of a new generation which ensures fuel cycles with low consumption of natural uranium ~0.196 kg/(MW·day). i.e., at the PWR level. Implementation of this problem requires the following: for VVÉR-1000 – – completion of work on the 4-yr fuel cycle with improved fuel assemblies with uranium–gadolinium fuel and burnup up to 55 MW·days/kg U and incorporation of this cycle in commercial operations; – production and incorporation of the construction of unjacketed fuel assembly with a rigid framework; – inclusion of recovered uranium in the fuel cycle;
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– completion of the commerical-test operation of an alternative variant of a fuel assembly construction and, if the results are positive, switch to a 4-yr fuel cycle in the No. 1 unit at the Kalinin nuclear power plant; for VVÉR-440 – – modernization of the fuel assembly construction; – commercial adoption of the 5-yr fuel cycle with uranium–gadolinium fuel; – incorporation of recovered uranium in the fuel cycle; for RBMK-1000, -1500 – – switching completely to uranium–erbium fuel in all units; – further optimization of the fuel cycle with uranium–erbium fuel to increase burnup; – incorporation of a construction with high operating reliability (with centrally secured fuel elements).
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