U.S. study on impacts of heterogeneous recycle in fast reactors on overall fuel cycle

Full text: The heterogeneous recycle approach in which driver fuel assemblies (containing Pu or Pu+Np) and target assemblies (containing the remaining minor actinides) are used in the fast reactor core is being considered as an alternative to the homogeneous recycle approach in which all transuranic elements (TRU) are contained in the driver fuel and no target assemblies are employed. By this separation of the plutonium and minor actinides (MA) in the heterogeneous recycle approach, these actinides can be managed separately in the transmutation system and the fuel cycle. Some advantages of the heterogeneous recycle approach include: (1) use of technology similar to existing recycle fuel fabrication and co-extraction processes for early deployment of advanced fuel cycle technology (permits time for additional R and D to find solutions to the handling of the high dose MA); (2) potential to confine the remote fabrication of MA-containing fuels with lower throughput to a dedicated sub-facility for fabrication; (3) easier fabrication of conventional recycle fuel form for driver assemblies (with the possibility that the first recycle of Pu or Pu+Np might not need to be remote); and (4) flexible management of MA loading in the core. There are however potential issues with the heterogeneous recycle approach related to the confinement of the high radioactivity and heating of the minor actinides in compact assemblies. Preliminary evaluations (mostly core studies) of the issues associated with the use of heterogeneous recycle in advanced fast reactor systems have been performed by U.S. national laboratories.In a follow on study, an evaluation of the impacts of the approach on the technologies proposed for the fuel cycle (including reactor, separations, and fuel fabrication and performance) is being undertaken by the laboratories. Issues currently being evaluated and to be discussed in the full paper include: (1) difficulty of recycling, handling, and fabricating target assemblies in the fuel cycle; (2) the state of target technology (fabrication, irradiation performance, etc.); (3)issues associated with MA storage (alternative to immediate use); (4) impacts on reactor performance and safety; and (5) impacts on the transmutation system dynamics and strategies. A quantitative estimation of the economic impact of target utilization is also planned. (author)