susceptible to Loss of Flow (LOFA) and Loss of Heat Sink (LOHS) accidents and therefore require additional measures to assure their safety. Moreover, the technology for the design of large accelerators and for their coupling with the reactor requires extensive development to improve the overall system reliability, capacity factors, and reduce the development and deployment costs. A 1999 DOE review of the US Accelerator Transmutation of Waste (ATW) program concluded that operation of an ATW prototype or demonstration unit might take as long as 20 years to implement and would cost as much as $11 billion. Full implementation of ATW in the United States for treating civilian spent nuclear fuel would require several decades and could cost hundreds of billions of dollars [Bresee J.C., 2003]. Production of electricity and improved resource utilization can partially offset the costs related to ADS technology. In addition, thermal spectrum molten salt fueled ADS, as pointed out in [Bowman C.D., 2000], may require up to 4 times smaller accelerator due to reduced neutron leakage and reduced reactivity control requirements which would also facilitate better economic performance of ADS. On the other hand, critical fast spectrum systems with carefully designed safety features may appear to be more favorable candidates for TRU transmutation as they can potentially provide comparable to ADS transmutation capabilities but at lower cost and with greater reliability due to utilization of more mature technologies [Hejzlar et al., 2003], [Romano A., et al., 2002].
Fuel Cycles The proposed fuel cycles for transmutation of waste differ in several respects. Depending on the main goal of transmutation Pu or Pu, MA, and LLFP can be considered. Suggested fuel cycle strategies also included single path with maximized deep burndown of TRU or multi-recycling of Pu and MA in one or multi-tier systems. Several examples of the proposed fuel cycles are presented in Figure 1.2.4. The concern over growing Pu stockpile from commercial LWR spent nuclear fuel in addition to significant quantities of weapons grade (WG) Pu from dismantled nuclear warheads [Albright D. et al., 1997] resulted in extensive research effort aiming at the reduction of the excess amounts
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