Gaining Reactivity to Extend Operation

Abstract

In October 2021, Point Lepreau Nuclear Generating Station (PLNGS) experienced an equipment reliability challenge which prevented the fueling machine from delivering fuel to the core. The following needed to be addressed:

• How can the Station extend high power operation without fueling the reactor in a safe and efficient way?
• What is the maximum power that can be produced to maintain safe Station operation without fueling (on a regular basis)?

Prior to the reactor being derated from 100% full power (FP) on 2021-10-29 at 22:00, the core was verified to have 2.1 mk of excess reactivity above 30% average zone level (AZL) fill, which is equal to 5.9 full power days (FPD).

Reactor power was reduced from 100%FP to 90%FP where PLNGS operated for six days. Then reactor power was further reduced to 82.2%FP where it operated for eight days until the AZL reached 29% zone level fill, while the simulation at 100%FP before the derate predicted 30% average zone level fill.

By comparing the core reactivity from daily fuel consumption using the energy clock to the AZL trend from Station measurement it has been confirmed that derating reactor power from 100%FP to 82.2%FP can extend reactor operation by one week. The extension arises from fission products moving towards new saturating levels following the power reduction.