A Multidimensional Multigroup Diffusion Model for the Determination of the Frequency-Dependent Field of View of a Neutron Detector

The sensitivity of a neutron detector to parametric fluctuations in the core of a reactor depends on the position and the frequency of the perturbation. The basic neutron diffusion model for the calculation of this so-called field of view (FOV) of the detector is extended with respect to the dimensionality of the problem and the number of energy groups involved. The physical meaning of the FOV concept is illustrated by means of some simple examples, which can be handled analytically. The possibility of calculating the FOV by a conventional neutron diffusion code is demonstrated. In that case, the calculation in n neutron energy groups leads to 2n modified neutron diffusion equations.