Experiences with MCNP, NJOY, and ENDF/B data

In recent years, there have been several releases of the cross-section processing code NJOY as well as two releases of the code MCNP, combinations of which are used in conjunction with the ENDF/B data, for bench-marking and analysis in several fields of applications. The NJOY code was updated several times for error corrections as well as updates to handle ENDF/B-VI data. One purpose of this study is to examine possible effects of the various combinations of these codes and data on typical light water reactor (LWR) calculations. In particular, any potential effects of the error corrections in NJOY (from version 89 through 91) on MCNP results for LWR calculations are examined. A comparison between versions V and VI of ENDF/B data is also made using an LWR critical experiment. Users of NJOY may also be aware that the Boltzmann constant used in the code is ∼2% lower than the value of 8.617 x 10-11 MeV/K. Unless explicitly corrected by the user, this could potentially lead to a temperature mismatch between NJOY-generated data and the temperature used in the MCNP input. This problem is also investigated in this study