Post-Irradiation Neutron Emissions From CANDU® Fuels and Their Nuclear Forensics Applications

Abstract

The operating conditions (coolant flows, temperatures, pressures) of the Heat Transport System (HTS) of a CANDU® reactor are affected by the aging of its components. For a given fuel bundle design, those changing conditions result in lower dryout powers, and in the absence of any corrective actions addressing the root cause of those changes, the decrease will continue as the aging of the HTS components progresses. As a result of this situation, safety margins for several relatively high frequency Design Basis Accidents (DBAs) in Deterministic Safety Analysis will also be decreasing as a function of time. Eventually, defence-in-depth will be compromised if no corrective actions are taken, and ultimately reactor de-ratings (reactor operating at less than 100% full power) will be required in order to ensure, for those postulated DBAs, that shutdown system effectiveness at protecting the integrity of physical barriers to the release of radioactive materials is maintained at all times. Depending on its size and duration, the economic impact of deratings on licensees could be significant.