A Code Comparison Study for the Bigten Critical Assembly

The performance of six popular continuous-energy Monte Carlo and multigroup transport codes has been compared for a simple spherical model of the Bigten critical assembly using ENDF/B-VII nuclear data. This “code comparison” exercise was supplemented with a few “data testing” results using different nuclear data evaluations. This particular critical assembly was chosen because it is sensitive to the U-238 unresolved resonance range, thus extending recent good results obtained for faster criticals like Godiva and Jezebel. After some improvements, the results showed generally good agreement between the codes, their differences being generally smaller than the differences between those seen when using different evaluated data libraries. This suggests that the current generation of codes is adequate for studying assemblies similar to Bigten and for evaluating the effects of possible improvements in the nuclear data libraries.