Spent Fuel Assembly Dimensions: Condiderations for Cask Designs

When designing casks for the shipment of Spent Nuclear Fuel (SNF), one of the most important considerations is the external dimensions of the fuel assemblies to be shipped. If the assemblies cannot fit within the cask, then the cask is of no use to either the utilities or to DOE. While the dimensions of \"standard fuel\" are specified in Title 10 Code of Federal Regulations Part 961 \"Standard Contract for Disposal of Spent Nuclear Fuel and/or High-Level Radioactive Waste,\" past cask designers have not used these dimensions in their designs. Additionally, SNF assemblies tend to grow and deform during irradiation, affecting the overall assembly envelope. The contract also allows non-fuel components to be shipped integral to the assemblies. There has been some debate over whether \"standard fuel\" dimensions are truly representative of the majority of SNF awaiting disposal. In preparation for the issuance of a request for proposals for contingency cask designs by the Civilian Radioactive Waste Management System (CRWMS) Maintenance and Operations (M&O) contractor, the author examined the factors which cause SNF assemblies to deviate from their pre-irradiation dimensions. These factors are identified and discussed with emphasis placed on how the fuel assembly dimensions are changed and the effects these changes have on cask design.