Creep Analysis of Aluminum-Based Spent Nuclear Fuel in Repository Storage

摘要

Aluminum-clad, aluminum-based spent nuclear fuels (Al SNF) from foreign and domestic research reactors are being consolidated at the Savannah River Site (SRS). These fuels are planned to be put into dry storage followed by disposal in the federal repository. Temperature conditions in storage and disposal systems due to nuclear decay heat sources will promote creep deformation of the fuel elements. Excessive deformation of the Al SNF will cause gross distortion (slump) of the fuels and may cause gross cladding rupture.The stress in the dry stored spent nuclear fuels is due to self-weight and is considerably low (several psi). Even under this low loading, significant creep strains in the fuel elements may take place over long time at elevated temperatures corresponding to geological repository disposal conditions. The creep (viscoplastic) strain in the fuel element is a function of temperature, grain size of the material, grain boundary diffusion activation energy and time. A parametric analysis was performed to investigate creep deformation response of the spent fuel assemblies to a range of temperatures. The Materials Test Reactor fuel element is precisely modeled for finite element analysis. Calculations cover temperatures from 100°C to 350°C for grain sizes of the aluminum cladding of 10 micro-meter and 50 micro-meter. Below 200°C for up to several decades, creep deformation is negligible. Significant distortion of the fuel elements is predicted within several years at a temperature of 350°C.