Validating JENDL-3.3 for Water-Reflected Low-Enriched Uranium Solution Systems Using STACY ICSBEP Benchmark Models

Evaluated criticality benchmark data obtained at the Static Criticality Experiment Facility (STACY) account for a large percentage of low-enriched uranium (LEU) solution systems documented in the "International Handbook of Evaluated Criticality Safety Benchmark Experiments." These data are available for validation of computer codes and nuclear data used for criticality safety analyses of LEU solution systems. The calculated k_eff's for the water-reflected STACY criticality experiments have been overestimated with JENDL-3.2 by ~0.7%. These overestimations were kept in mind while making modifications of the fission spectrum and the fission cross section of ²³⁵U, and the (n,p) cross section of ¹⁴N in JENDL-3.3. Because of these modifications, the k_eff's calculated with JENDL-3.3 were largely improved. The contributions of these modifications in JENDL-3.3 with respect to JENDL-3.2 and ENDF/B-VI.5 were investigated by performing perturbation calculations. The overestimation of the elastic-scattering cross section of ⁵⁶Fe in the mega-electron-volt range was one of the reasons for the k_eff overestimations for the STACY experiments with JENDL-3.2. The modification of ⁵⁶Fe cross sections in JENDL-3.3 reduces k_eff's in the STACY experiments by 0.2%. The dependence of calculated k_eff's on uranium concentration still exists in JENDL-3.3. The overestimation of calculated k_eff's for the STACY experiments with JENDL-3.3 is not insignificant and is as much as 0.6%. These problems are to be resolved in a future evaluation of the cross-section library.