BN-800 design validation and construction status

Information is presented on the BN-800 design, the second design following BN-600, power-generating unit with a fast reactor. The main stages of the development of the design begun in the 1980s, modified in the 1990s after the Chernobyl accident, and accepted for construction within the government program starting in 2000 are presented. The fundamental differences of BN-800 from BN-600 are characterized, and current R&D work is briefly described. Information is presented on the construction of BN-800 at the Beloyarskaya nuclear power plant, where the BN-600 has been operating since 1980.     

Concept of an advanced power-generating unit with a BN-1200 sodium-cooled fast reactor

The status of work on the development of a 1200 MW sodium-cooled reactor facility for serial construction is presented. The general characteristics of the facility and the power-generating unit as well as the objectives which must be attained as a result of the design are presented. The design of the power-generating group is based on solutions some of which have been checked during the operation of sodium-cooled reactors in Russia and some have been validated by the appropriate research and development work performed for BN-800. At the same time, new solutions are used which are aimed at improving the technical-economic indicators and increasing the level of safety. Additional R&D work will be needed to validate them.     

Neutron-induced swelling and embrittlement of pure iron and pure nickel irradiated in the BN-350 and BOR-60 fast reactors

Pure iron and nickel were irradiated in the range of 2-15 × 10⁻⁷ dpa/s at 345-650 °C to very high neutron exposures in two fast reactors, BOR-60 and BN-350, to study void swelling and changes in mechanical properties of these two metals. Both nickel and iron swell in this temperature range with the maximum swelling rate at ∼500 °C in nickel, but possibly at ?350 °C for iron. It also appears that the swelling rate in nickel and possibly in iron may be dependent on the dpa rate, increasing with decreasing dpa rate. The evolution of mechanical properties of the two metals is quite different. The differences reflect the fact that b.c.c. iron is subject to a low-temperature embrittlement arising from a shift in ductile-brittle transition temperature, while f.c.c. nickel is not. Nickel, however, exhibits high temperature embrittlement, thought to arise from the collection of transmutant helium gas at the grain boundaries. Iron is not strongly affected by transmutation since it generates much less helium during equivalent irradiation.     

Operation experience of the BN-600 fast reactor

This paper presents the main operating experience of the BN-600 Power Unit, which has been under operation since 1980 as a part of the Beloyarsk Nuclear Power Plant situated in Zarechny town, Sverdlovsk Region, Russia.Theperformance of the core, the reactor, the fuel handling systems, the steam generator unit, the sodium and steam circuits, and the electrical equipment is highlighted. The technological procedures and the events which occurred, including sodium leaks, are also considered.     

Behavior of vibrationally compacted mixed fuel in BN-800

The modified computer code MACROS was used to study the behavior of fuel elements with vibrationally compacted mixed fuel under irradiation in BN-800. Verification calculations were performed for fuel elements irradiated in BN-600 under close to nominal conditions. Attention was focused mainly on the factors playing an important role in their serviceability: swelling, creep, corrosion behavior of cladding, temperature distribution, gas-release, and degree of structural reformation of the fuel core.     

Fuel for advanced sodium-cooled fast reactors: current status and plans

Different fuel compositions have been irradiated in the BR-10, BOR-60, BN-350, and BN-600 reactors and investigated: PuO₂, UC, UN, UPuN, UO₂, UPuO₂, metallic doped and undoped alloys, and fuel compositions with inert matrices. Studies of fuel elements with UPuN as well as with fuel compositions based in MgO and ZrN irradiated in the BOR-60 reactor were completed in 2009. The main results of the investigations of different fuel compositions are presented and the problems of ensuring the serviceability of BN-800 and -1200 fuel elements are discussed.     

Intrinsic Safety of Future BN-800 Based Nuclear Technology

More than 40 years of experience in performing research and development work and operation of fast sodium-cooled reactors is analyzed. It is shown that such reactors possess a system of intrinsic safety properties, making possible long-time reliable operation and reducing to a minimum the consequences of an accident.A BN-800 unit under construction with the core switched to nitride fuel can serve as a basis for nuclear technology with intrinsic safety in accordance with the requirements of the strategy for the development of nuclear power in Russia in the first half of the 21st century.     

BN-800 as a New Stage in the Development of Fast Sodium-Cooled Reactors

The role of fast reactors in a strategy for developing nuclear power in Russia because of the inevitable exhaustion of natural uranium deposits in the foreseeable future is discussed. The BN-800 reactor, which is under construction and incorporates unique solutions – greatly enhancing the safety of the reactor – to technical and constructional problems, is examined. Cost assessments taking account of the complete life cycle show that fast reactors could be no more expensive than the most widely reactors in the world – water-moderated water-cooled reactors.Closing the BN-800 nuclear fuel cycle will make it possible to solve the problem of utilizing plutonium and actinides. This makes fast reactors safer for the environment.     

Safety of sodium-cooled fast reactors

Conclusions The accumulated experience in the operation of NPP, including those with fast reactors, shows that during normal operation, with due regard for possible operational difficulties and accidents, they ensure a significantly lower level of risk for personnel and the surrounding population than is present in industrial regions and those prone to natural disasters. Therefore, the dangers connected with the widespread development of nuclear power arise not so much from a real risk as from a risk which in principle can be realized in very improbable accidents. From this point of view sodium-cooled fast reactors have certain advantages. The probability of the maximum accident of the rupture of pipelines in high-pressure reactors must be considerably higher. Here a single event, and one difficult to detect, such as the failure to detect a flaw in manufacture, is enough to initiate the very dangerous first step of an accident. The rupture of equipment in the primary loop of a fast reactor at practically atmospheric pressure is considerably less probable, and the integral assembly is quite safe. All the other chains of development of maximum accidents in a fast reactor require the simultaneous realization of several events in systems and devices which are constantly being monitored (SS and power supply systems, etc.). The above considerations together with such important properties of sodium as the large reserve before the boiling point and the practically inertialess transport of heat from the reactor to structural elements and heat-transfer devices under natural circulation conditions gives one confidence that the level of risk for future industrial NPP with fast reactors will be at least no higher than that for NPP with thermal reactors.Translated from Atomnaya Énergiya, Vol. 43, No. 6, pp. 464–472, December, 1977.     

Aspects of the economics of fast reactors

Conclusions At present, the thermal reactors have the economic advantage. The gain in the fuel component of fast reactors, it must still be acknowledged, still cannot compensate the loss in the specific capital investments, because the contribution of the fuel component to the cost of electricity is now small. However, in the future, as the uranium produced becomes more expensive, the situation should change in favor of fast reactors. It is difficult to predict when such an economic inversion will occur, because, as we have pointed out, the real, experimentally confirmed, data on the costs of serially produced fast reactors as well as the cost of the external fuel cycle, optimized for these reactors, are not available. There are no reliable predictions of the increase in expenditures on uranium production. At the same time, the technical problems of fast reactors will require a long period of time to work out in scale, at least because of the need for guarantee reliable assimilation of the sodium coolant on industrial scales and also because deep burnup of fuel must be ensured. Experience in developing and operating commercial BN-350 and −600 reactors has been positive. The construction of small, serially produced, fast reactors should continue, even if they will formally remain economically less advantageous, for some time, than the already well-assimilated serially-produced thermal reactors. The main problem here will be to improve the technology of both the reactors themselves and the external fuel cycle. In this respect the prospects are good in both cases. At the same time, allowance must be made for the fact that the inversion of the economic advantage will probably occur even before the end of the service life of the currently designed, serially-produced, first-generation fast reactors. Then these reactors will be more advantageous. Translated from Atomnaya énergiya, Vol. 80, No. 5, 345–350, May, 1996.