ANSI/ANS-8.12 Revision: Selection of MOX Critical Experiments and Preliminary Validation Results

摘要

The validation exercise described herein shows that there is a sufficient number of benchmark experiments to validate the optimally moderated subcritical limits in the revision to ANS-8.12. For the damp (3 wt% H_2O) cases, the relative lack of benchmarks appears to necessitate loosening the applicability filter and including benchmarks of dubious applicability. This is especially true for the high-Pu content cases (AOA DriHiP), where the lack of highly applicable benchmarks leads to an unacceptably low USL of 0.9055. A detailed study of benchmark trends indicates that there is good coverage across most of the parametric ranges needed to support the 108 applications. The exception is for the 0 wt% ~(240)Pu (P0) cases for damp MOX powders (AOAs DriHiP and DriLoP); this is true even if the less applicable benchmarks as discussed in Table 2 are included. One final issue that has been raised concerns the fact that the benchmarks may be highly correlated, especially given they are drawn in some cases from a small number of benchmark sets. The best method of dealing with that, and selection of the final subcritical margin upon which limits in the revised ANS-8.12 standard will be based, remains to be determined.