Thermal Analysis of a Proposed Transport Cask for Three Advanced Burner Reactor Used Fuel Assemblies

Preliminary studies of used fuel generated in the US Department of Energy’s Advanced Fuel Cycle Initiative have indicated that current used fuel transport casks may be insufficient for the transportation of said fuel. This work considers transport of three 5-year-cooled oxide Advanced Burner Reactor used fuel assemblies with a burn-up of 160 MWD/kg. A transport cask designed to carry these assemblies is proposed. This design employs a 7-cm-thick lead gamma shield and a 20-cm-thick NS-4-FR composite neutron shield. The temperature profile within the cask, from its center to its exterior surface, is determined by two dimensional computational fluid dynamics simulations of conduction, convection, and radiation within the cask. Simulations are performed for a cask with a smooth external surface and various neutron shield thicknesses. Separate simulations are performed for a cask with a corrugated external surface and a neutron shield thickness that satisfies shielding constraints. Resulting temperature profiles indicate that a three-assembly cask with a smooth external surface will meet fuel cladding temperature requirements but will cause outer surface temperatures to exceed the regulatory limit. A cask with a corrugated external surface will not exceed the limits for both the fuel cladding and outer surface temperatures. INTRODUCTION The Advanced Fuel Cycle Initiative (AFCI) is an effort to develop advanced nuclear fuel cycles [1] in which recycling of used nuclear fuel (UNF) sustains the fuel source and minimizes deposition of waste into geologic repositories. In such a cycle, used light water reactor (LWR) fuel is recycled for reuse in an Advanced Burner Reactor (ABR). Many process steps in proposed AFCI fuel cycles require transportation of used fuel. These include but are not limited to transportation from LWR plants to separations facilities; from separations facilities to facilities performing recycling, storage, enrichment and fuel fabrication; and from recycling facilities to ABR plants. Concerns with safety and security during transportation of UNF are raised due to high radioactivity and possible proliferation. These concerns are addressed in part by minimizing instances of fuel in transit, that is, by shipping as much fuel as possible during a single transportation operation. This decreases the frequency at which costly safety and security measures are taken. Current once-through fuel cycles already require transportation of fresh and used fuel and are designed to address these issues. However, differences between LWR and ABR fuel composition and higher levels of radioactivity and heat generation of used ABR fuel pose difficulties that are not accommodated by existing transportation infrastructure. UNF is currently transported by truck or rail in large transport casks. These casks surround the fuel by several layers of radiation shielding. A single cask can transport anywhere Proceedings of the ASME 2010 Pressure Vessels & i i i i i / f r July 18-22, 201 , ll , i t ,