Reactor operation induced thermal effects on neutron flux measurements using $^3$He neutron detectors at a TRIGA Mk II research reactor

Abstract

A variation of the measured neutron flux using $^3$He detectors at a TRIGA Mk II nuclear research reactor during steady-state operation is reported in this article. The observed effect shows a statistically significant anti-correlation between the temperature in the reactor pool and recorded neutron counts. Following reactor start-up under nominal operating conditions, the effect occurs for a specific time period until thermal equilibrium and a constant neutron count rate are reached. Simultaneous neutron and temperature measurements are performed in different configurations around the reactor in order to gain qualitative insights about the temperature dependent count rate behavior. Possible origins of the effect are identified and further measurements for a more detailed investigation are suggested.