BURNUP CREDIT IN SPENT FUEL STORAGE AND TRANSPORTATION: REGULATORY PERSPECTIVE ON CURRENT STATUS AND FUTURE DEVELOPMENTS

Allowance in the criticality safety analysis of spent fuel storage and transportation systems for the decrease in fuel reactivity resulting from irradiation is termed burnup credit. Extensive investigations have been performed both within the United States and by other countries in an effort to understand and document the technical issues related to the use of burnup credit. To address technical issues associated with Pressurized Water Reactor (PWR) fuel burnup credit, the U.S. Nuclear Regulatory Commission (NRC) issued Interim Staff Guidance 8, Revision 3, Burnup Credit in the Criticality Safety Analyses of PWR Spent Fuel in Transportation and Storage Casks, in October of 2012. This paper will outline the significant changes in this guidance document from the previous revision, and the technical basis behind them. Additionally, although burnup credit has been used to some degree in Boiling Water Reactor (BWR) spent fuel pools, it has not yet been requested for BWR spent fuel dry storage or transportation system designs. In anticipation of receiving such requests, the NRC is initiating a long-term BWR burnup credit research project. This project will investigate the various technical issues associated with BWR burnup credit that differ from PWR burnup credit, such as: control blade exposure during irradiation, varying axial moderator density, use of burnable poison rods, varying axial and pin enrichments, and partial length rods. The conclusion of this research will be a set of conclusions and recommendations regarding calculation assumptions and analytical methods for BWR burnup credit, which will be incorporated into revised NRC guidance. This paper will describe the technical issues associated with BWR burnup credit, and outline the plans for the research program to address them.