Determination of in-core power in low energy research reactors by measurement of16N and18F in the primary coolant

Abstract

The measurement of16N and18F activity in the primary coolant of the JASON Argonaut reactor has been used to monitor in-core reactor power. The16N is produced by the16O(n, p)16N reaction and the 6.1 MeV photopeak was measured on-line using a BGO detector adjacent to the primary coolant circuit. These data provided a relative measure of power stability during steady state operation and a measure of linearity at different power levels. The18F is produced in the primary coolant by the18O(p, n)18F reaction and aliquots of primary coolant were sampled from the reactor dump tank for off-line radiochemical analysis. The18F was separated as trimethylfluorosilane and the activity was determined by measurement of the 0.511 MeV annihilation photopeak using a NaI(TI) detector. The measured18F activity was used to determine actual in-core reactor power using both ab-initio calculations and by comparison of results with a calibrated power reactor. The18F data also provided a method of nomalising the16N data for direct monitoring of in-core reactor power in JASON.