Analysis of the Burnup Credit Benchmark with an Updated WIMS-D Library

The OECD/NEA Burnup Credit Benchmark was analysed with the WIMSD5B code using a fully updated library based on ENDF/B-VI Revision 5 data. Parts-IA and IB were considered. The criticality prediction tested in Part-I A was in very good agreement with the reference result. A slight trend to overestimate the absorption rate by the fission products was noted, which can be explained by spectral effects resulting from the coarseness of the WIMS-D 69-group energy grid. The isotopic composition prediction tested in Part-IB was within the uncertainty interval of the reference results, except for 109 Ag at lower burnup and 155Gd in all the cases. For 109 Ag the cause of the discrepancy was the use of old fission yield data in generating the reference solution. Similarly for 155Gd the difference was due to old 155 Eu capture cross sections. Compared to the measurements, a serious underprediction of Sm isotopes is observed. This could be due to problems in the measured values or in the nuclear data of Sm precursors. We conclude that our processing methods do not introduce significant errors to the basic nuclear data. Care should be taken in the interpretation of the reference average benchmark solution due to a possible bias towards the ENDF/B-V evaluated nuclear data files.