Anticipated Improved Performance of Advanced Steel Cladding Under Long Term Dry Storage of Spent Fuel

In current light water reactors the nuclear fuel rods are dependent on zirconium alloys cladding. Used fuel bundles are generally stored in water pools for approximately twenty years and then they may be transferred to a dry casket for an interim storage until reprocessing or the final disposition in a permanent nuclear waste repository. The delay in opening a permanent repository in the US says that the used fuel bundles would need to be stored in dry casks for unanticipated extended periods (maybe 100 years). Under dry storage several mechanisms were identified for the degradation of zirconium based cladding. The vulnerabilities of zirconium alloys would limit their subsequent fuel retrievability and transportation after the long term storage. As part of the DOE Accident Tolerant Fuel (ATF), advanced ferritic steels such as Fe-Cr-Al alloys are being investigated to replace the zirconium alloy cladding. Previous performance in storage of austenitic stainless steel cladding suggests that the proposed ATF ferritic steels would perform well under long term storage in dry casks.