This paper describes the validation of fast neutron transport calculations for Magnox RPVs operated by Nuclear Electric. The work compares calculated data, derived using the Monte Carlo code McBEND, with extensive plant measurements. Agreement is typically within ∼20%.

This level of agreement has been achieved using individual models for the top, side and bottom of each reactor in which almost explicit representation of all the major components was required. The modelling detail included the geometric effects of temperature and irradiation on reactor components as well as source data derived from reactor measurements and operating histories. Such effort is justified because the reduced uncertainty in the pressure vessel dose can be translated into increased operating margins and extended plant lifetimes.