Fast Spectrum Reactor

The fast-spectrum reactors with full recycle of actinides would be designed with on-site spent fuel reprocessing and fuel fabrication to minimize the on-site inventory of long-lived radioactive waste. Modern robotic equipment can be used for reactor refueling and for fuel reprocessing. The spent fuel reprocessing and fuel fabrication facilities must be developed to close the nuclear fuel cycle and use all the energy available in natural uranium. 

The Westcott formulation for the effective cross sections a and a is useful only for well-moderated thermal reactors, where the approximations of the neutron spectra ate more reasonable. Even in such reactors, more detailed calculations of actual neutron spectra and effective cross sections are necessary for precise reactor design. The Westcott cross sections are not applicable to fast-spectrum reactors, where neutron moderation and thermalization are suppressed. 

Because lead is chemically inert with the water required to generate steam for power production, and because the vapor pressure of lead is extremely low, lead-cooled reactors do not require the massive containment structures of LWRs and thus have the potential to be less expensive than current LWR technology, particularly if refueling occurs at greater than 10-year intervals. In whatever form, improvements in fast-spectrum reactor technology and the ability to pro-... 

Although helium gas was used in the previous illustration, similar arguments can be made for CO2 as a coolant. Carbon dioxide has been the preferred coolant for the magnox and AGR reactors helium is required for high-temperature reactors using graphite as a moderator and either helium or CO2 might be used in a fast-spectrum reactor. The choice of a gas coolant for a particular reactor can depend on heat-transfer considerations, chemical and radiation stabUity, and interaction effects, or perhaps other factors. 

Studies on the gas-cooled, fast-spectrum reactor have shown that a potential advantage of carbide fuel over oxide is derived from its increased conductivity, increased heavy metal density, and decreased moderating effect. The improved conductivity of the carbide over the oxide may allow the maximum heat removal per foot of fuel element to be raised from 20 to about 40 kW/ft. Increased heavy metal density and decreased moderating effect of the carbide allow the possibility of a harder neutron spectrum and therefore an increase of about 10% in the breeding ratio. 

The last row in Table X shows the uranium requirements assuming a complete economy of gas-cooled, fast-spectrum reactors. The conditions shown are typical of those calculated for such a reactor (/4). Under these conditions, the doubling time for breeding would be about eight years, whereas that for reactor installation is assumed to be six years, so that a net consumption of uranium (for this particular assumed buildup rate) would be required, even for this reactor. 

The supercritical-water-cooled reactor (SCWR) ( Fig. 58.21) system features two fuel cycle options the first is an open cycle with a thermal neutron spectrum reactor the second is a closed cycle with a fast-neutron spectmm reactor and full actinide recycle. Both options use a high-temperature, high-pressure, water-cooled reactor that operates above the thermodynamic critical point of water (22.1 MPa, 374°C) to achieve a thermal efficiency approaching 44%. The fuel cycle for the thermal option is a once-through uranium cycle. The fast-spectrum option uses central fuel cycle facilities based on advanced aqueous processing for actinide recycle. The fast-spectrum option depends upon the materials R D success to support a fast-spectrum reactor. 

Material and structural issues to be addressed are primarily related to the potential for corrosion and stress corrosion cracking under irradiation at the high temperatures and pressures associated with the SCWR. Materials for cladding and structural components must be identified and tested to demonstrate their performance in thermal and fast-spectrum reactors. Radiolysis and water chemistry at supercritical conditions must be investigated to understand the effect on reactor materials. Specific material properties to be investigated include dimensional and microstructure stability, and strength, embrittlement, and creep resistance characteristics of the materials. 

From 2003 to 2007, a number of potential UREX + flowsheets for the processing of commercial UNF were developed and tested with actual UNF at laboratory-scale at Argonne National Laboratory (Regalbuto, 2011 Vandegrift, 2007) (Table 14.13). The UREX + 1 series was intended for the extraction of the TRU elements as a group there is no separation among the TRUs which are to be burned as fuel in fast spectrum reactors (FR). 

One of the concepts, the water cooled ELENA (1), is being designed for district heating as its primary function. Another two concepts, the water cooled UNITHERM (2) and the sodium cooled RAPID (3), are being designed for a variety of applications, including cogeneration options with potable water and/or district heat production. All three concepts are sized for remotely sited towns of several tens to one hundred thousand populations two are water cooled thermal spectrum reactors, one is a sodium cooled fast spectrum reactor. Their characteristics are summarized in Table 3. 

Essentially, closed cycle fast reactors with a breeding ratio of slightly above 1.0 can operate using depleted uranium as fuel and this would be the case for both small and large sized fast spectrum reactors with CR > 1 in a closed fuel cycle with multiple recycling of transuranics. 

As indicated by Table 2 and several design descriptions given in the annexes, achieving a CR >1 appears feasible in the several concepts of small fast-spectrum reactors with lead and lead bismuth coolant, especially when dense nitride fuel is employed. Should it work out in practice, such reactors will not loose to larger-size LMFBRs in the efficiency of uranium ore... 

The small fast spectrum reactors could fission minor actinide content of the TRU as fuel whereas in LWR MOX recycle, the minor actinides act as neutron parasitic absorbers, which either precludes their use in LWRs and necessitates them to be stored after recovery or would require a new inert matrix fuel be developed for LWRs and... 

Achieving a smooth transition from a fully open cycle, fuelled from an external supply of to a fully closed cycle, self-fuelled from breeding of secondary fissile material, requires a careful management of the time evolution of deployments of thermal- and fast-spectrum reactors such that the fractions of net consumers and net generators of fissile mass in the overall nuclear park can simultaneously ... 

Despite the fact that the proposed reactor technology is backed by a long design and operating experience of the lead-bismuth cooled reactors for nuclear submarines and the fast spectrum reactors with sodium coolant for NPPs it is still innovative for civil nuclear power. Therefore, additional validation and testing, as well as licensing would be required. 

Helium is the traditional high temperature, high pressure gas coolant. Liquid fluoride salts are a traditional high temperature, low pressure liquid coolant. The only other potential candidates are liquid metals, particularly molten lead or lead alloys for fast spectrum reactors. Because of their relatively low boiling points, traditional liquid metals such as sodium are not candidates for high temperature operations. 

Volumes I and II, Nuclear Energy Research Advisory Committee, Subcommittee on Generation IV Technology Planning A Roadmap to Deploy New Nuclear Power Plants in the United States by 2010, 2002. U.S. DOE Office of Nuclear Energy, Science and Technology. Waltar, A., Todd, D., Tsvetkov, P. (Eds.), 2012. Fast Spectrum Reactors. Springer, ISBN 978-1-4419-9572-8. 

Alan E. Waltar, Donald R. Todd, Pavel V. Tsvetkov (Eds.), Fast Spectrum Reactors, Springer Verlag, 2012, ISBN 978-1-4419-9571-1. 

The second class of innovative concepts is liqnid metal-cooled fast-spectrum reactors ( fast-spectrum refers to the energy of the neutrons in the reactor core). In a typical reactor, a moderator (usually water, which pulls double-duty as both neutron moderator and reactor coolant) is nsed to slow down neutrons because slower neutrons are more efficient at causing fission in U-235. In a fast-spectrum reactor, there is no moderator. Instead, it relies on higher energy neutrons, which are less effective at causing uranium to fission but are more effective at causing fission in plutonium and other heavy elements. For this reason, these reactors are not ideal for a uranium-based fuel cycle but they are quite suitable for use with a fuel cycle based on plutonium and the other heavy... 

Most fast-spectrum reactors operated around the world use liquid sodium metal as a coolant. Future fast-spectrum reactors may use lead or a lead-bismuth alloy, or even helium, as a coolant. One of the attractive properties of metals as coolants is that they offer exceptional heat-transfer properties in addition, some (but not all) metal coolants are much less corrosive than water. However, because sodium is reactive with air and water, fast-spectrum reactors built to date have a secondary sodium system to isolate the sodium coolant in the reactor from the water in the electricity-producing steam system. The need for a secondary system has raised capital costs for fast reactors and has limited thermal efficiencies to the range of 32 to 38 percent. Novel steam-generator designs, direct gas cycles, and different coolants are options that may eliminate the need for this secondary sodium loop and improve the economics of fast reactors (Lake et al 2002). 

Because of the mix of fissile and fissionable isotopes that develops after several recycling steps, fuel from multiple recycling steps is best suited for fast-spectrum reactors. In a fast-spectrum reactor, neutrons retain relatively high energy from birth (via fission) to death (via absorption or escape). Fast-spec-... 

The fast spectrum reactor system sizing is sensitive to fuel loading capability in the core and the void space interfaces to the reflector... 

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