Application of a Monte-Carlo Simulation Code for the Research and Development of Self-.Powered Flux Detectors

Abstract

Self-powered flux detectors (SPFDs) are used for flux mapping, control and safety in Canadian power reactors and are thus a key element of the CANDU concept. To facilitate the design and development of SPFDs without having to resort to excessive experimentation, a Monte-Carlo simulation Code was written some years ago to compute the gamma ray and neutron responses of detectors. The Code is given the acronym ICARES, which stands for Irradiated Cable Response Simulation. This paper reviews the Monte-Carlo simulation of the actual physical processes that occur inside a SPFD. The various current producing mechanisms, electron transport and the calculation of detector sensitivity will be briefly described. Two applications of the ICARES Code to the development of SPFDs will be presented. The first is to the development of a prompt- neutron-sensitive flux-mapping detector using iron or titanium as the emitter material. A detector of this type would make possible a flux-mapping system that generates a flux map for a power reactor with prompt response and have the potential of allowing higher accuracy in the setting of flux related trip parameters. Simulation results for detectors using iron and titanium emitters are compared. The second application is to the calculation of the sensitivity of a larger-outside-diameter lead cable for SPFDs. A manufacturer has proposed increasing the diameter of the lead cable by 50% due to manufacturing difficulties with the transition zone (the region of the detector where the detector's outer sheath reduces from 3 mm OD over the emitter to 1 mm OD over the lead cable). Calculation of the revised sensitivity of the larger cable will be presented.