Nuclear Science and Engineering / Volume 145 / Number 1 / September 2003 / Pages 132-144
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 keff'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 keff'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 keff overestimations for the STACY experiments with JENDL-3.2. The modification of 56Fe cross sections in JENDL-3.3 reduces keff's in the STACY experiments by 0.2%. The dependence of calculated keff's on uranium concentration still exists in JENDL-3.3. The overestimation of calculated keff'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.