How inelastic scattering stimulates nonlinear reactor core parameter behaviour

Nonlinear and skewed distributions for safety-related parameters of a realistic Pressurized Water Reactor (PWR) are observed due to the current limited knowledge of the inelastic scattering of neutrons on 238U. The current knowledge of this cross section, about 20% uncertainty, does not lead to normally distributed core parameters, thus increasing the probability of rare events. In this paper, it is demonstrated how the simulations of 14 years of PWR operation with realistic history and fuel loading pattern induce non-Normal distributions for 3-dimensional peaking quantities and why a reduction of the 238U inelastic cross section uncertainty by a factor 2 is desirable.