Study of the Effect of Integral Burnable Absorbers for PWR Burnup Credit

The Interim Staff Guidance on burnup credit issued by the U.S. Nuclear Regulatory Commission's Spent Fuel Project Office recommends restricting the use of burnup credit to assemblies that have not used burnable absorbers. This restriction eliminates a large portion of the currently discharged spent fuel assemblies from cask loading, and thus severely limits the practical usefulness of burnup credit. This report examines the effect of integral burnable absorbers (IBAs) on reactivity to provide technical justification for relaxing the current restriction for dry storage and transportation, and subsequently, for developing the necessary guidelines for relaxing the current restriction. The effect of IBAs on reactivity for various IBA designs is shown and discussed. Further, the reactivity effect of IBAs for typical initial fuel enrichment and absorber loadings is quantified as a function of burnup. The report concludes with a discussion of the issues for consideration and preliminary recommendations to expand the use of burnup credit to include spent fuel assemblies with IBAs.