Status Update: Elevated Radiation Fields in the Primary Heat Transport System at the Point Lepreau Nuclear Generating Station

Abstract

Routine dose-rate measurements taken since the refurbishment of the Point Lepreau CANDU-6 reactor had shown radiation fields at the reactor face and at some locations removed from the reactor core were three-to-four times higher than expected in 2014-2015, based upon plant experience prior to refurbishment. This finding was unexpected since much of the historical inventory of ⁶⁰Co and other long-lived radionuclides would have been removed when the plant was refurbished. Preliminary assessments identified the primary source as the short-lived radionuclides ⁹⁵Zr and ⁹⁵Nb and confirmed that they were most likely released from the pressure tubes, not the fuel bundles. This paper describes the steps undertaken by PLNGS to understand and mitigate the evolution of primary heat transport system radiation fields, which included analyses from PHTS crud sampling, purification filter deposits and IX resin and, modelling of corrosion product and activity transport. While the radiation fields seem to have plateaued and declined slightly, the mechanisms involved promoting release and distribution of these isotopes around the PHTS are still unresolved.