Density fluctuations in simple stochastic reactor models

A method to study density fluctuations in a nuclear reactor simultaneously taking into account intrinsic fluctuations usually modelled by a master equation and parametric noise usually modelled by stochastic kinetic equations is presented. The mean density and density-fluctuations variance are calculated for a simple point-reactor model in the presence of Gaussian white-noise fluctuations in the fission, capture and source event rates. They are also calculated in the case of dichotomous noise fluctuations in the source event rate. 'Crossed fluctuation' contributions to the density fluctuations are found that only appear when considering simultaneously intrinsic and parametric noise. These contributions allow distinction to be made between reactivity fluctuations due to fission-rate and capture-rate fluctuations. (author)