Th/U-233 multi-recycle in PWRs.

The use of thorium in current or advanced light water reactors (LWRs) has been of interest in recent years. These interests have been associated with the need to increase nuclear fuel resources and the perceived non-proliferation advantages of the utilization of thorium in the fuel cycle. Various options have been considered for the use of thorium in the LWR fuel cycle including: (1) its use in a once-through fuel cycle to replace non-fissile uranium or to extend fuel burnup due to its attractive fertile material conversion, (2) its use for fissile plutonium burning in limited recycle cores, and (3) its advantage in limiting the transuranic elements to be disposed off in a repository (if only Th/U-233 fuel is used). The possibility for thorium utilization in multirecycle system has also been considered by various researchers, primarily because of the potential for near breeders with Th/U-233 in the thermal energy range. The objective of this project is to evaluate the potential of the Th/U-233 fuel multirecycle in current LWRs, with focus this year on pressurized water reactors (PWRs). In this work, approaches for ensuring a sustainable multirecycle without the need for external source of makeup fissile material have been investigated. The intent is to achieve a design that allows existing PWRs to be used with minimal modifications. In all cases including homogeneous and heterogeneous assembly designs, the assembly pitch is kept consistent with that of the current PWRs (21.5 cm used). Because of design difficulties associated with using the same geometry and dimensions as a PWR core, the potential modifications (other than assembly pitch) that would be needed for PWRs to ensure a sustainable multirecycle system have been investigated and characterized. Additionally, the implications of the use of thorium on the LWR fuel cycle are discussed. In Section 2, background information on studies evaluating the use of thorium in the fuel cycle is provided, but focusing on Th/U-233 multirecycle. Recent studies done internationally and in the U.S. are briefly summarized. Additionally, the previous U.S. thorium breeder experiment in the Shippingport reactor is briefly discussed. The objective of this work and the reactor design issues associated with multirecycle of Th/U-233 are discussed in Section 3. The approaches required to achieve a sustainable system are discussed and evaluated. Homogeneous assembly modeling results are presented in this section. In Section 4, a 17-by-17 heterogeneous assembly design has been selected and evaluated, based on its positive attributes for sustainable Th/U-233 multirecycle. A feasibility study is briefly discussed at the end of this section followed by recommendations for future activities. Section 5 discusses the attributes of the 17-by-17 heterogeneous assembly design. The material mass flow data and fuel cycle impact data are reported in this section. Discussions on the fuel cycle implications of thorium fuel utilization are provided in Section 6. This includes information on fuel sources, fuel manufacturing, fuel reprocessing, and re-fabrication. The conclusions of the study are provided in Section 7