The sodium-cooled fast reactor (SFR) uses a closed fuel cycle. Because it is a closed cycle system, its primary benefits are effective actinide management to minimize waste toxicity and optimal use of fuel through recycling. SFR is a relatively well-developed technology. Developments include the Phenix end-of — life tests planned in France, the restart of the Monju reactor in Japan, the lifetime extension of BN-600 and start-up of BN-800 in Russia, and the start-up of the China Experimental Fast Reactor (CEFR). The overall GIF plan for the SFR within Generation IV (Fig. 13.15) is based on optimization of design and operating parameters within the next few years, the building and testing of SFR plants by 2015 and commercial operation by about 2020 (Lineberry and Allen, 2002). There are three possible layout options for the reactor unit:

1 a small size (50 to 150 MWe) modular-type reactor with U-Pu-MA-Zr metal alloy fuel, supported by a fuel cycle based on pyrometallurgical processing in facilities integrated with the reactor

2 an intermediate-to-large size (300 to 1500 MWe) pool-type reactor with oxide or metal fuel

3 a large size (600 to 1500 MWe) loop-type reactor with mixed U-Pu oxide fuel and potentially MAs, supported by a fuel cycle based upon advanced aqueous processing at a central location serving a number of reactors

Figures 13.16 and 13.17 show two of the larger plant designs. Fluids that offer high performance in terms of thermal efficiency, safety and reliability include water/steam, supercritical carbon dioxide and, more recently, molten salt. Liquid sodium is used as a coolant in SFRs, enabling high power density with a low coolant volume fraction. Because sodium reacts with air and water, a sealed coolant system is required. The oxygen-free environment has the added benefit of preventing corrosion. The outlet temperature range is 500-550 °C, which is suitable for existing materials developed and tested in earlier fast reactor programs. The SFR closed fuel cycle enables regeneration of fissile fuel and facilitates management of high-level waste, particularly Pu and MAs. Its fast neutron spectrum will extend available U resources in comparison with thermal

AHX

chimney

PDRC

piping

13.16 Pool-type KALIMER (600 MWe) SFR.

reactors. Fast spectrum reactors like SFRs have the capacity to exploit almost all of the energy present in U versus the 1% utilized in conventional thermal spectrum systems (Lineberry and Allen, 2002). Fast reactors also offer a unique solution to the problem of actinide management because they operate with high-energy neutrons that are more effective at fissioning transuranic actinides. Key properties relating to actinide management include:

• consumption of TRUs in a closed fuel cycle, thereby lowering the radiotoxicity and heat load, and so facilitating waste disposal and geologic isolation

• more efficient use of U resources through multi-recycling and better management of fissile materials

• high level of safety through inherent and passive means that accommodate transients and bounding events with significant safety margins

Issues that need further research include improving safety by the reduction or even elimination of routes that can lead to severe hypothetical core disruptive accidents (CDAs). Another issue is cost. Recent studies have estimated that the capital cost of current designs may be 25% greater than conventional LWRs. Capital costs can be reduced through a combination of simpler configuration, advanced fuels and materials, and refined safety systems. There is a need to improve the management of waste generation, including improved thermal efficiency, better utilization of fuel resources, and development of superior waste forms for the SFR closed fuel cycle. Reducing the amount of waste generated from operations, maintenance and decommissioning is also an important goal, as is limiting environmental discharges and improving proliferation resistance (Vezzoni, 2011; Sagayama, 2011). There is also a need to develop ion exchange systems for reducing the volume of ceramic material required (Lineberry and Allen, 2002).