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NUCLEAR POWER OF FAST REACTORS: A NEW START
Victor V. Orlov,
N.A. Dollezhal Research and Development Institute of Power Engineering (NIKIET),
There was no acute need for a new energy source in the 20th century. The fuel balance, economics, and safety of nuclear power combined to make the goal of its development much more difficult to attain as compared with the military objectives of nuclear weapons accomplished by the U.S. and then by U.S.S.R. in the 1940s–1950s.163
But Enrico Fermi’s idea (1944) of a nuclear power industry comprised of fast reactors – which promised a new era of energy production, that of inexpensive electricity derived from cheap and inexhaustible fuel and used in inexpensive nuclear power plants (NPP) – still remains appealing. The experimental EBR-I reactor (Argonne National Laboratory [ANL]) produced the first nuclear electricity as early as 1951, and the first successful NPPs with fast neutrons, the BN-350 (1972-1997) and BN-600 (1980), were developed by Alexander Leipunsky in the 1960s.164
In the 1950s, Russia, the UK, the United States, and Canada brought into operation the first power plants with ‘military’ thermal reactors as a first stage in nuclear power development and as a source of plutonium (Pu) production for fast reactors. Encouraged by the successes of military engineering, nuclear power quickly progressed from a conceptual idea of physics to a technology and an industry with an applied scientific network to serve it. The nuclear engineers, trained to deal with reactors developed in the 1940s–1950s, had to improve the safety of thermal reactor facilities in the 1970s–1980s, which made their cost four times higher. The early fast reactor plants turned out to be even more expensive and saw no succession. Nuclear power entered the 21st century in a state of stagnation, with uncertain prospects for the future.165
With oil and gas prices rising, many states are now cautiously returning to electricity based on a new generation of thermal reactors: the United States and Europe, Russia have announced a large VVER construction program, and India and China are actively assimilating the above technologies in their ambitious nuclear programs). However, without returning to the original idea of nuclear power based on fast reactors (FR), it will be difficult to cope with the looming fuel and energy problems of the 21st century. Although resulting in only an incremental increase in their cost, the recent improvements of thermal NPPs will not be sufficient to meet future demands. It will first be necessary to re-examine the reason for the failure of the original idea, which lies in the very ‘fast breeder’ concept developed by ANL in the 1940s: namely, the
163
With costly chemical fuel of limited availability, electricity is much more expensive than heat; it still accounts for a mere 1/6 of the energy consumed (1/3 in fuel consumption) and its share shows slow growth.
164
Fast reactors (FRs) are a scientific concept and may be the basis of future large-scale nuclear power plants. Thermal reactors (TRs) will most likely be used to address local and other needs. It should be noted that the best fuel for TRs is Th-3U from thorium blankets of FRs.
165
Massachusetts Institute of Technology (MIT), “The Future of Nuclear Technology,” (Boston: MIT, 2003). Available at http://web.mit.edu/nuclearpower/; accessed July 13, 2008.
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underestimation of safety issues.
By the end of the 1980s, analysis of previous industry experience led N.A. Dollezhal Research and Development Institute for Power Engineering (NIKIET) physicists and designers, under the direction of the Director Evgeny Adamov, to abandon the ‘fast breeder’ in favor of the ‘fast reactor of natural safety’166 (BREST). Based on advances achieved since the 1950s–1960s, these physicists proceeded with engineering designs for the following:
equilibrium FR operation with breeding ratios (BR) of approximately 1 (the advantages of which were understood as early as the 1960s)
the use of nitride, rather than the oxide fuels used in the early FR (e.g. metal fuel used at ANL)
on-site dry reprocessing (Scientific Research Institute of Atomic Reactors; Idaho National Laboratory) instead of the aqueous process used in military applications
non-combustible, molten Pb coolants (based on experience with Pb-Bi for submarines) rather than Na
By the end of the 1990s, Minatom prepared the Nuclear Power Development Strategy and the technical basis for the Initiative of the Russian President at the United Nations with a brief political statement of objectives.167
Compared to other countries, Russia is better prepared to create a fast reactor capable of resolving fuel and energy problems. The technical and financial issues are manageable; more difficult to overcome are the negative connotations and unfavourable economics that came to prevail in the industry during the decades of stagnation.
Although a great deal of Pu has accumulated already and its breeding, in the short-term, will not be necessary, it will be difficult to move forward without revising the ‘fast breeder’ concept. This could be done by simple estimation, but it would be improper and inconclusive without referring first to the greatest primary source–Fermi.168
THE ORIGIN OF THE FAST BREEDER STEREOTYPE
In April 1944, the separation plant at Oak Ridge was not yet in operation, and in his first outline for fast reactor-based nuclear power Fermi decided against the energy-consuming and expensive separation of uranium isotopes. Fast reactors would not run on natural uranium, so he started with a parent graphite or heavy-water-moderated thermal reactor, which would rapidly consume uranium and produce little Pu. Then, as fast reactors were brought into operation, they would initially run on the Pu from these thermal reactors and then ‘multiply’ or ‘breed’ their own
166
Equivalent to ‘inherent safety’ extended to waste and proliferation. In the 1970s, Alvin Weinberg predicted a “moratorium” for construction of new nuclear power plants in the U.S. and later envisioned a new start of nuclear power with inherently safe nuclear plants; in reality, however, the whole effort was reduced to the development of “passive” reactor safety features. “Continuing the Nuclear Dialogue: Selected Essays,” American Nuclear Society, 1985.
167
United Nations Millennium Summit, 2000. For further information, see http://www.un.org/millennium/; accessed July 13, 2008.
168
Enrico Fermi, “Discussion on Breeding,” Scientific Works of Enrico Fermi [Russian translation], (Moscow: Nauka 1972), V. 2, pp. 220–224.
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required fuel (uranium blanket, BR>1).
Fermi was not convinced of his preliminary estimates, and the changeover to enriched uranium was not unlikely. Besides, he felt that “the public may not accept an energy source that is encumbered by vast amounts of radioactivity, and that produces a nuclear explosive, which may fall into hostile hands.”169
Before long, the uranium enrichment process, used for weapons production matured. This was further developed for nuclear submarine and thermal power reactors in the 1950s. Even simple assessments show that it would be better to start fast reactors on enriched uranium if only to reduce uranium consumption, to say nothing of the safety implications (estimates for modern light water reactors are given below).170 A breeding ratio of approximately 1 would be sufficient (with BR~1.05 being optimal),171 and fast reactors of moderate power density would naturally go into equilibrium ‘burning’ of U238, Pu, and minor actinides (MA). This would facilitate the resolution of safety problems (NPP, waste, proliferation) with the ensuing reduction of NPP costs. Although he was present during the start-up of EBR-I in 1951, Fermi himself never returned to the development of fast reactors. Instead, he delegated their development to ANL, where his outline evolved into the fast breeder concept, including:
Uranium blanket with weapons-grade Pu, and BR>1, which led to the reactivity margin ∆K>>βeff, with the risk of a prompt criticality excursion, and to separation of uranium and Pu in reprocessing
high fuel power density P and breeding rates ω~(BR-1)P
heat removal by light-weight and heat-conducting (but combustible and neutron-moderating) Na, which has a relatively low boiling point (Tboil ~ 900°C), close-packed lattice of fuel rods in tight shrouds; worse thermal hydraulics; flow blockage danger
Consequently, the inherent safety properties of FRs were left untapped. As with thermal reactors, the present-day fast neutron machines are also potentially prone to severe accidents, involving a prompt criticality excursion, loss of coolant with the additional hazards of Na exposure to air and water, and positive void effect in the event of rapid Na boiling. Moreover, the problems of waste and proliferation remain unresolved, and the FRs cost even more than the expensive thermal reactor facilities. Nevertheless, the idea of Pu breeding, which appeared correct at first glance, was embraced by major physicists. Eventually, this came into general use, was included in educational programs, and became a universally ingrained stereotype.
169
Ibid.
170
A 1 gigawatt (GW) light water reactor (LWR) with high burnup consumes 10 kt of natural uranium and generates about 7 tons of fissile Pu over 50 years. The latter allows integrating 1 GW from FRs into a closed nuclear fuel cycle (NFC) with about one year of cooling. The efficiency of U235 in FRs is a factor of 1.3-1.4 lower than that of Pu, so it would take about 10 tons of U235 (derived from 2 kt of natural uranium) to integrate 1 GW from FRs based on natural uranium into a closed NFC, which is 5-6 times less than that required for a “parent” TR, with the same being nearly true for separation work units.
171
The 16 Mt of “cheap” uranium allows for the deployment of LWRs to a capacity of 1.6 thousand GWe (gigawatts electricity) (~20 percent of electricity) in the 21st century, while FRs would provide more than 8,000 GWe (with more expensive uranium being also acceptable). FRs with a Th blanket in the future could provide another several thousand GW from TRs. Given breeding rations of ω~1 percent per year, nuclear power could grow to a level higher than 105 GWt (10 kW [kilowatt] per capita for 12 billion people, as in advanced countries). It is hardly necessary to seek more, nor is it advisable (from the standpoint of a balance with 108 GW of incident solar radiation).
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Plutonium breeding is no longer of importance today, but instead of revising the FR concept and going back to Fermi’s idea, some experts are ready to abandon FRs and the closed nuclear fuel cycle (NFC) altogether, thus depriving nuclear power of a future.172 Others (such as those developing the Global Nuclear Energy Partnership)173 are looking into possible special applications for fast reactors (incineration of actinides, or small reactors with infrequent refuelling). There is yet a third category of experts (for example, those working within the Generation IV International Forum) who seek to keep the FR option open, and are counting on engineering improvements made by trial-and-error, (some of them rather radical, such as substituting gas, water of Pb for changeover from Na).174
Some scientists (of the Kurchatov Institute, and OKBM) are still insisting on high breeding for FRs, carrying this idea to the extreme of a fast reactor as a ‘Pu factory’ to cater to thermal reactors, which is both physically and economically unsound.
Fast reactors do not have enough neutrons to provide many TRs with Pu (their quantity would be sufficient for potential fusion reactors or expensive accelerator-driven systems). But the FR will also be expensive if its neutrons and design features are keyed to attaining BR>>1 to feed one TR rather than to resolving safety problems; it would be cheaper to use more expensive uranium.
The idea of the ‘Pu factory’ gave way to one of a ‘diverse nuclear power mix’ consisting of TRs, FRs, and MA ‘burners.’175 Fast reactors could accomplish the latter if not for the prevalence of TRs for some obscure reasons.
Experts would not be forced to rely on computer models if experimental work on new fast reactors had not been forsaken. Without advancing from the reactors of the 1950s–1960s, Russia will not be able to maintain its leadership, indeed its independence, in nuclear engineering.
Due to the availability of inexpensive fuel, the operation of existing NPPs is profitable and the earnings are sufficient to justify their life extension and renovation. Although it is expensive to build new VVERs, their decommissioning will start after 50-60 years of operation, and it is only a changeover to FRs in a closed NFC that can justify the budgetary expenses. To pave the way for such a changeover, the Nuclear Power Strategy made provisions for building BREST-300 and BN-800 on the Beloyarsk NPP site, with both reactors running on nitride fuel and sharing the same fuel cycle facilities with non-aqueous reprocessing.176
172
MIT, The Future of Nuclear Power. The Russian Corporation TVEL notes that “(t)he closed nuclear cycle envisages transportation of irradiated fuel assemblies to radiochemical plants to extract unburned uranium rather than transportation to disposal site. Recoverable uranium could amount up to 95 percent of initial uranium mass. Then, this material is subject to same processing stages as the one mined.” Presently the majority of countries use an open fuel cycle. For more information, see http://www.tvel.ru/en/nuclear_power/nuclear_fuel_cycle/; accessed April 6, 2008.
173
For further information regarding the U.S. Global Nuclear Energy Partnership, see http://nuclear.inl.gov/gnep/index.shtml; accessed April 6, 2008.
174
Gas and supercritical water allow a single-circuit design of a FR, but its fuel must feature exceptional reliability. The microfuel concept of TRs is not suitable for FRs which, with no clear alternative, would mean changing one hazard (Na) for another (high pressure). For further information regarding Generation IV International Forum (GIF), see http://gif.inel.gov/; accessed May 1, 2008.
175
Minor actinide “burners” would be necessary in a small-scale nuclear power industry in which FRs are absent or are a long time in coming.
176
Strategy of the Development of Nuclear Power Engineering of Russia in the First Half of the 21st Century. Basic Provisions, Ministry of the Russian Federation for Atomic Energy, Moscow, 2000, approved by the Government of the Russian Federation on May 25, 2000, Protocol No. 17 (Moscow: Minatom Rossii, 2000).
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Implementation of the Strategy’s objectives was reduced entirely to the BN-800 alone, which is being built practically along the lines of the oxide-fuelled BN-600 designed in the 1960s. It is still unclear what sort of closed NFC will be used, even though its preparation is the sole purpose for building the expensive BN-800. It will be impossible to exactly monitor the circulation of thousands of tons of 5U and plutonium should nuclear power expand to produce thousands of gigawatts (GW); the equipment is capable of extracting 5U and Pu. Therefore only technical and political palliatives can be used to control proliferation. Reprocessing of equilibrium composition fuel in fast reactors (closed fuel cycle) does not involve very deep purification, which can be done by coarse physical extraction methods of light-mass fusion products to avoid separation of mass-like U, Pu, and minor actinides. This makes it possible to exclude the most hazardous technologies of plutonium separation and uranium enrichment to maintain non-proliferation and to adopt a comprehensive ban on and the elimination of nuclear weapons by the states party to the Treaty on Non-Proliferation of Nuclear Weapons.177
CLOSED NUCLEAR FUEL CYCLE OF FAST REACTORS
The enrichment, burnup and, hence, the activity of FR fuel, which are much higher than in TRs, make the aqueous process developed for extraction of weapons-grade Pu (that most suitable for thermal reactors) hardly suitable in a closed NFC of fast reactors due to:
low critical concentration of Pu in aqueous solutions
decomposition of organic extracting agents
easy uranium and Pu separation
large quantities of liquid radioactive waste
steep increase in the cost of shipping radioactive and fissile materials
long cooling periods for spent fuel before transportation and reprocessing
many-fold increase of Pu quantities required for starting FRs in a closed NFC
Thorough removal of fission products is not essential for FRs, nor is removal of MA.
With the time taken for spent nuclear fuel cooling, transportation, reprocessing, and return to the reactor optimistically estimated at seven years (fuel lifetime for the BN is about 1.5 years, as compared to the above estimate of one year), Pu consumption in starting up a 1 GW fast reactor in a closed cycle would triple from seven to more than 20 times.
In this case, a 1 GW VVER can give rise to 1/3 GW in FRs instead of 1 GW. When the VVERs are then taken out of service in the second part of the 21st century, the nuclear generating capacity will drop to 1/3 of its previous level. An increase in the breeding ratios would not correct this, as the average Pu power density in the closed fuel cycle will become three times lower as will the breeding rates (from ω~ 3 percent to less than 1 percent per year, given BR = 1.2). Although all of the above was well-known in the 1960s, when the United States and Russia initiated research on on-site ‘dry’ reprocessing for the closed fuel cycle of FRs, it was apparently forgotten over the past 40 years.
177
To read the text of the Treaty on the Non-Proliferation of Nuclear Weapons, see http://www.iaea.org/Publications/Documents/Infcircs/Others/infcirc140.pdf; accessed April 6, 2008.
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There are no grounds for giving up the Strategy target of an on-site NFC for the BREST-300 and BN-800 reactors at Beloyarsk; it is necessary to resume the work interrupted six years ago and to do it urgently, if for no other reason than justifying the budgetary expenses for the costly BN-800. With much time lost already, a provisional solution will have to be found for making the first core for the BN-800, with the enriched uranium option not to be overlooked, if the reactor is going to be commissioned in 2012.
FAST REACTOR FUEL
The neutron balance, enrichment and, consequently, power density of a FR (which is much higher than in TRs) call for a high-density, heat-conducting, heat- and radiation-resistant ceramic fuel. It is for this reason that in 1965, PuO2 of BR-5 (loaded in 1959) was changed to UC and then to UN, and UPuN fuel rods were tested. The initial purpose was to increase the breeding rate, and the tests were performed under loads far in excess of those for oxides (400-500 W/cm) at temperatures above 1500°C, where nitride dissociation begins (with nitrogen pressure growth).
With the idea of high breeding abandoned, moderate loads were adopted for BREST with temperatures in the fuel rod middle below 900°C, where neither the above nor other problems, such as Pu transport and interaction with steels, may arise. Given low O and C concentrations, nitride shows insignificant swelling and releases far less gas than oxides; besides, a sufficient gap in the fuel relieves the cladding of mechanical loads and contributes to higher burn-up.178
The Bochvar All-Russian Scientific Research Institute for Inorganic Materials developed a process and built a line for BREST fuel rod fabrication, and if this work had not been nearly stopped six years ago, experts in Russia would have approached completion of the tests in BOR-60 and BN-600 today. Yet, the BREST fuel tests in the BOR-60 (with the burnup so far as low as 3 percent) have been staged. Examination of the fuel rods revealed local interaction of the “internal” Pb (without oxygen) with the cladding. It seems clear how the problem may be resolved but there are no funds for conducting the experiments. Given normal funding, completion of the development work and validation of the BREST fuel design would take five or six years at most, which would provide FRs, including the BN-800, with the fuel that can significantly enhance their safety and economics.
Statements to the effect that the fuel that has been studied for four decades will have to be developed over another 20 to 30 years, are coming from a period of stagnation. It is true that serious developments were made a long time ago, but the importance of the objective calls for a resumption of this effort.
178
The problem of nitrides lies in the formation of the environmentally hazardous 14C from 14N in the (n,p) reaction. A changeover to 15N would eliminate this problem and improve the neutron balance, considering that separation of N isotopes is not overly expensive. However, this option is left for the future: ‘dry’ reprocessing does not give rise to CO2, and if radioactive waste is buried in stable forms, 14C would account for a mere 1 percent of the waste radiotoxicity.
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COOLANT
The situation is equally dire not only for the closed cycle and the fuel of FRs, but also for the completion of the research and development on Pb, started 19 years ago under our initiative at the Institute of Physics and Power Engineering (IPPE), Central Scientific Research Institute of Structural Materials (CNIIKM) and other institutes.
The advantages of non-combustible Pb over Na are obvious from the standpoint of safety, if not entirely so in terms of thermal hydraulics (e.g. weight, heat conductivity). A systems approach – often referred to by F.M. Mitenkov179 – necessitates that all major factors should be taken into account, including neutron moderation, which is much lower with heavy Pb than with Na. It is therefore possible to considerably increase the Pb volume inside the lattice (and the flow area) and to have a lower flow velocity. As compared with Na, this results in smaller hydraulic resistance and pumping power requirements, and a temperature gain – up to 120°C for BREST – with an increase of Tin to 420°C and a sufficient margin over the melting temperature of 327°C (which means that Pb-Bi is unnecessary).
Heavy Pb is actually better than Na in terms of thermal hydraulics, except for the case of high heat fluxes to be removed, where heat conductivity is of substantial importance (which must have been the reason for ANL to choose Na). But this characteristic is not so important if high breeding rates are abandoned, and the cladding temperature in the “hot spot” is reduced in a BREST reactor of moderate power density180 from over 700°C in BN down to 650°C, acceptable for ferritic-martensitic steels, which – besides being low-swelling – are resistant to Pb under proper oxygen control.
The main problems with Pb lie in adapting the Pb-Bi technology developed for submarines and in testing the steels designed for use in Pb-Bi for corrosion resistance to Pb. Positive results have already been obtained for the core materials at IPPE (17 thousand hours) and for the circuits at CNIIKM. It is an important finding that the potential considerable upward and downward variations from the nominal oxygen concentration over hundreds of hours of operation will not lead to dangerous corrosion development. The problems of ‘stagnant zones’ and mechanical damage to oxide films appear to be resolved by appropriate design, but this conclusion requires experimental verification.
For the prototype BREST-300 to be built it is necessary to complete the suspended equipment development program, which will take five to six years. If not for this interruption, the BREST-300 would already be under construction and Russia would have been building the nuclear power industry on a truly new technological basis.
CONCLUSION
In the 1940s, it was hard to avoid mistakes, then firmly fixed in a stereotype of fast breeder reactors started with Pu from thermal reactors. As a result, this vision of the nuclear
179
F.M. Mitenkov, “Prospects for the Development of Fast Breeder Reactors,” Atomic Energy, V. 92, June 6, 2002, pp. 453-460.
180
OKBM has also significantly reduced the BN power density in its newer designs and may, hopefully, take other steps towards natural safety.
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power industry has not been implemented in the 20th century and without new FRs the industry won’t be able to considerably influence the resolution of the fuel, energy, and environmental problems facing the world in the 21st century.
Although endowed with rich fuel resources, Russia’s high per capita energy consumption (on par with other highly developed countries) and low energy efficiency will require a shift to greater innovation in the 21st century to overcome the raw materials deviation in the economy, export operations, and society structure. This can be achieved through the development and deployment of fast reactors in the nuclear power industry. The Strategy 2000 provides for a shift to FRs;181 it should be updated with time, but more importantly, it should be implemented despite the presence of certain stereotypes and special interests.
Development of a prototype BREST-300 with a closed fuel cycle, followed by the development of the first BREST NPP within the next 20 years would give rise to an innovative new power industry. The objectives underlying the further development of BREST and its associated technologies (with some studies already underway and others to be initiated) include:
changeover from the supercritical steam-turbine to the medium-pressure gas-turbine cycle consistent with the principles of natural safety
changeover from chemical removal of fission products to physical (plasma) processes, to rule out the possibility of uranium and Pu separation
generation of high fast-reactor process heats (800°C and up) with Pb (Tboil up to 2000°C), assuming availability of heat- and radiation-resistant materials (STAR-H2 concept, ANL)
conversion of the fast reactors to “continuous” refuelling to reduce the reactivity margins, increase the capacity factor, etc. (new refuelling system)
adaptation of NPP design rules and regulations to the requirements of natural safety for full use of the economic advantages offered by FRs
future provision of fast reactors with a Th blanket to supply Th-U233 fuel to TRs, which may be preferable in remote regions and smaller countries
utilization of NPP heat and radionuclides for domestic, industrial, agricultural and medical purposes
configuration of nuclear power complexes with FRs, a closed fuel cycle, facilities for radioactive waste treatment, radionuclide and heat utilization, and physical protection systems
radiation-equivalent disposal of waste from the equilibrium NFC of fast reactors in naturally radioactive formations of former uranium mining sites
scientific and political aspects of transition to nuclear power based on FRs in an equilibrium closed and equilibrated NFC, which offers the prospects of independent energy development to large countries
If ensured of such prospects, nations may be willing, in the common interests of non-proliferation, to resort to the services of nuclear states or international centers for uranium enrichment, reprocessing of TR fuel, and fabrication of the first FR cores during the transition period.
181
Strategy of the Development of Nuclear Power Engineering of Russia in the First Half of the 21st Century. Basic Provisions
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This would allow more from political palliatives to radical and legal resolution of the problem of a comprehensive ban on elimination of nuclear weapons, with effective measures taken to control and suppress illegal nuclear activities by joint efforts, without nuclear or non-nuclear classification of nations.
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