Monte Carlo Modeling of Count Rates and Defects in a Silicon Carbide Detector Neutron Monitor System, Highlighting GT-MHR

Abstract

Focusing on the gas turbine-modular helium reactor (GT-MHR), we have developed methods to predict the positions in a nuclear reactor where silicon carbide (SiC) semiconductor diode detectors may work functionally as neutron monitors for at least one refueling cycle. Using MCNP and TRIM, we determined the count rate due to fast neutron-induced primary knock-on atoms and tritons, and the number of displacement damage defects that are created per count and over a refueling cycle, for SiC diode detectors placed at four different radial locations in the central reflector of the GT-MHR. We found that although the total count rates for the SiC detectors placed in locations close to the fuel elements were highest (˜1.2 × 106 counts/s), at those locations the detectors cannot tolerate the damage caused by fast neutrons for a reactor refueling cycle. On the contrary, for SiC detectors placed at the center of the central reflector, where the thermal neutron flux is the dominant flux component, the detectors can survive a GT-MHR refueling cycle. At this location, the total count rate for the SiC diode detectors that we have analyzed is ˜1.6 × 105 counts/s.