Comparison of Cross Section Data Library for High Temperature using MCNPX

MCNPX is a common computer code that applies Monte Carlo method and uses pointwise cross section data in term of ACE format processed from Evaluated Nuclear Data File (ENDF) library to simulate nuclear-related problems. ENDF library was released by the U.S. Cross Section Evaluation Working Group (CSEWG), contains nuclear reaction data of almost 400 isotopes obtaining from experimental data and theoretical predictions. However, the ENDF/ B-VI library basically provides neutron cross section at temperature 0K. To simulate a system at a higher temperature, the TMP card in MCNPX must be used to adjust the temperature of the system. According to MCNPX manual, the TMP card is only applied to neutron elastic and total cross section, then there is a significant error in calculated results caused by the Doppler-broadening effect on absorption cross section. To eliminating the error, a new cross section data for MCNPX is processed from ENDF library at specifying temperature by users. The library lwtr.62t of SAB2002 was applied for H₂O cross section in MCNPX calculations. There are two types of fuel assembly model were used for calculation, one without Burnable Absorber (BA) and other having 8% enrichment of BA (Gd₂O₃). The results calculated by MCNPX using ENDF/B-VI-NJOY cross section were compared with the results calculated by cross section library from endf60, endf66b, and endf70e package (ENDF/B-VI) applying TMP card to adjust cross section temperature. In addition, the results from ENDF/B-VI-NJOY calculation were also compared with the results of the same fuel assembly models calculated by two-dimensional transport code CASMO-4, which uses 70 energy groups cross section data processed from ENDF/ B-VI library. In summary, this study shows the method of customizing the cross section library for MCNPX matching with a special condition of a simulation model. The result from the benchmark problem calculation shown the usability of ENDF/B-VI-NJOY cross section. Compared with the ENDF/B-VI cross section, ENDF/B-VI-NJOY cross section reflects the effect of Doppler Broadening more than ENDF/B-VI. However, there is a noticeable error between MCNPX results and CASMO-4 results.