Assessment of Aging Mechanisms for Stainless Steel-and Al-Based Neutron Absorbing Materials Used in Spent Nuclear Fuel Dry Cask Storage Systems

摘要

At operating and decommissioned reactors, as well as independent spent fuel storage installations, in the United States, spent nuclear fuel (SNF) can be stored in sealed dry cask storage systems. Criticality of the SNF in the systems can be prevented, in part, by the placement of neutron absorbing materials (NAMs) around the SNF assemblies. NAMs include borated stainless steel, borated Al-based alloys, Al-boron carbide metal-matrix composites, and Al-boron carbide laminate composites (cermets). Integrity of the NAMs could potentially be affected by fatigue, neutron absorber depletion, thermal aging, general corrosion, creep, and radiation embrittlement. Cermets also are susceptible to wet corrosion and blistering. The results of this evaluation indicate that the aging mechanisms should have little or no effect on the NAMs' integrity in a dry cask system if they are not used as structural components, with the possible exception of wet corrosion and blistering of cermets caused by reactions between Al and water trapped in the porous matrix of NAMs at temperatures above 200 °C. Because the system temperature decays over time and the storage internal environment is likely to become free of water, the progression of the corrosion and blistering is likely to be arrested within 60 years. This paper presents an assessment of these aging mechanisms under the influence of the dry storage system internal environment and the aging effects on NAMs' integrity.