Speaker
Description
The COG suite of criticality benchmarks has been formally expanded to 3,368 to cover the entire energy range from thermal to fast neutron spectra under a variety of reflector and moderator conditions and fissile materials. The number of benchmark cases in each of these six major categories is summarized in Table 1.
Table 1. Number of Benchmark Cases.
Category Number of Cases
PU 766
HEU 1,046
IEU 206
LEU 801
233U 193
Mixed 356
Total 3,368
COG results have been compared with benchmark values from the International Criticality Safety Benchmark Evaluation Project Handbook for ENDF/B-VII.1, ENDF/B-VIII.0 and JEFF-3.3. COG results have been also compared with a MERCURY validation suite. Most of the results agree with the benchmark values within ±3σ. Among the three cross section data, cases with ENDF/B-VIII.0 performed best with about 85% of the total cases within ±3σ range. Sources of error may come from 1) cross section data, 2) possible errors from modeling of the experiments, or 3) errors in the benchmark evaluation or the experiments themselves. A major inter-comparison project between COG, MCNP, MORET, and SCALE for ENDF/B-VIII.0 and JEFF-3.3 is on-going. Inter-comparison with MERCURY is just beginning. LLNL participation in this project will result in development of significantly more COG benchmark cases as our goal is to overlap the VALID, WHISPER, and IRSN compendia of criticality benchmarks to the extent possible, which will be beneficial to international code user communities.
ACKNOWLEDGMENTS
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was funded by the U.S. Department of Energy Nuclear Criticality Safety Program.