Validation of the 172 group ENDFB7GX library

Full text: Five 172 group libraries, viz., IAEAGX, ENDFB6GX, JENDL3GX, JEFF31GX, and LWRPSGX were obtained as a part of the IAEA WIMS Library Update Project (WLUP). The first four libraries have data available for 173 nuclides up to 244Cm. The LWRPSGX library based on JEFF3.1 point dataset is an extended library up to 252Cf. Data for 12 more actinides and the related burnup chain were added. The five libraries were validated against known experiments in an earlier work. In general the LWRPSGX was found to be giving better results. Recently another version of 172 group library 'ENDFB7GX' has been released. In the present work we provide the results of validation of the ENDFB7GX library against the same set of experimental data and a comparison with results of other libraries. The experimental configuration data include a variety of uniform lattices with enriched UO2, U- metal, mixed oxide (UO2-PuO2) fuels with H2O and D2O moderators for a wide range of enrichment, fuel diameter and ratio of moderator to fuel volume (Vm/Vf). The calculations have been done using the code LATTEST which solves the single pin lattice cell problem by 1-D multi-group transport theory after cylindricalising the square or hexagonal cell boundary. The LATTEST code is an improved version of the MURLI code and is capable of providing a ready testing of any new cross section library against a set of experimental benchmark lattices collected from various sources. The calculated keff values and certain spectral indices, where available, have been compared for all the libraries for more than hundred critical lattices. There is a general under prediction of keff values by all libraries. The maximum under prediction is for ENDFB6GX library and the least is for JENDL3GX library. The ENDFB7GX library, in general, is found to over predict in comparison to the keff values obtained using LWRPSGX library. While scrutinizing the basic nuclear data it was noted that the slowing down cross section of hydrogen is higher by 1-2% in the fast/resonance energy range while the upscattering from thermal energy groups is less by 15-20% for H bound in H2O in the ENDFB7GX/LWRPSGX libraries compared to ENDFB6GX library. Due to increased slowing down and decreased upscattering in H, the spectrum tends to get softer and hence there is a gain in keff values while using ENDFB7GX/LWRPSGX libraries