Spent Fuel Burnup Credit in Casks: An NRC Perspective

Until now, the Nuclear Regulatory Commission's (NRC) approval of criticality safety evaluations for spent fuel in transport and storage casks has been based on analyzing the fuel as though it were fresh and without burnable poisons. The well-known nuclide composition of fresh fuel has provided a straightforward and bounding approach for showing that spent fuel systems will remain subcritical under normal and accident conditions. Burnup credit refers to the approval of criticality safety evaluations that consider the decrease in fuel reactivity caused by. irradiation in the reactor. Extensive investigations have been performed in the U.S. and other countries to understand and document the technical issues related to bumup credit. This paper reviews the background for NRC's efforts toward applying burnup credit in the licensing of casks for spent fuel from pressurized water reactors, discusses technical issues affecting the evolving NRC guidance in this area, and outlines the information and efforts needed to further expand such applications of burnup credit.