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Bias Estimates Used in Lieu of Validation of Fission Products and Minor Actinides in MCNP Keff Calculations for PWR Burnup Credit Casks (NUREG/CR-7205, ORNL/TM-2012/544)

Publication Type
Technical Report

The U.S. Nuclear Regulatory Commission Division of Spent Fuel Management issued Interim Staff Guidance (ISG) 8, Revision 3 in September 2012. This ISG provides guidance for NRC Staff review of burnup credit analyses supporting transport and dry storage of pressurized water reactor spent nuclear fuel (SNF) in casks. ISG-8, Rev. 3 includes, among other things, guidance for addressing validation of criticality (keff) calculations crediting the presence of a limited set of fission products and minor actinides (FP&MA). Based on previous work documented in NUREG/CR-7109, ISG-8, Rev. 3 includes a recommendation to accept use of 1.5 or 3% of the FP&MA worth, depending on the criticality code and cross-section data used, to conservatively account for the bias and bias uncertainty associated with the selected insufficiently validated FP&MAs. This bias is applied in addition to the bias and bias uncertainty resulting from validation of keff calculations for the major actinides in SNF. The work described in this report involves comparison of FP&MA worths calculated using SCALE and Monte Carlo N-Particle (MCNP) with Evaluated Nuclear Data Files, Part B–V, –VI, and –VII based nuclear data. The comparison supports use of the 1.5% FP&MA worth bias when either SCALE or MCNP codes are used for criticality calculations, provided the other conditions of ISG-8, Rev. 3, Recommendation 4 are met. The additional conditions include that the cask design is similar to the hypothetical generic burnup credit-32 cask model and that the credited FP&MA worth is no more than 0.1 Δkeff.