Speaker
Description
Recent experimental data measurements, namely transmission and (n, alpha), have motivated revising the O16 resonance region evaluation. Issues with the normalization of the (n, alpha) cross sections have been investigated and a very dependable measurement has been carried out at the GELINA facility at the Joint Research Center Geel from the energy threshold (2.354 MeV) to 9 MeV. Additionally, transmission measurements were done at the nELBE time of flight facility at Helmholtz-Zentrum Dresden - Rossendorf (HZDR). Experimental data used in previous evaluation were also considered in the evaluation.
The resonance evaluation was performed in the energy range from 0 eV to 6 MeV using the computer code SAMMY resulting in a set of resonance parameters (RPs) that describes well the experimental data used in the evaluation. The recent transmission measurements and the (n, alpha) cross section data are well reproduced in the RPs. The RPs were converted to the evaluated nuclear data file (ENDF) format using the R-Matrix Limited format option LRF=7. The intent of the full paper is to describe the procedures used in the evaluation of the RPs and the use of the RPs in calculations of critical benchmark experiments. Preliminary results for Pu-SOL-THERM-041 (PST-041) configurations listed in the International Criticality Safety Benchmark Evaluation Project (ICSBEP) handbook indicates an improvement on the average keff values with calculated keff being consistent with the benchmark keff, discrepancies on keff not exceeding the combined effect of experimental and Monte Carlo uncertainties. This series of 40 experiments performed at Valduc research center involves solutions of low 240Pu content (3 %) plutonium nitrate with a concentration in plutonium varying between 20 g/L and 190 g/L, in a 500 mm/200 mm annular tank. In particular, for the PST-041 series the changes in keff values indicate that these benchmarks are sensitive to the (n, alpha) cross section of 16O and that the new measurements were essential to improve the benchmark results.