Long-term Performance of the CANDU-type of Vanadium Self-powered Neutron Detectors in NRU

Abstract

The CANDU-type of in-core vanadium self-powered neutron flux detectors have been installed in NRU to monitor the axial neutron flux distributions adjacent to the loop fuel test sites since 1996. This paper describes how the thermal neutron fluxes were measured at two monitoring sites, and presents a method of correcting the vanadium burn-up effect, which can be up to 2 to 3% per year, depending on the detector locations in the reactor. It also presents the results of measurements from neutron flux detectors that have operated for over eight-years in NRU. There is good agreement between the measured and simulated neutron fluxes, to within + 6.5%, and the long-term performance of the CANDU-type of vanadium neutron flux detectors in NRU is satisfactory.