Adjuster Absorber Rods Return to Service at PLNGS

Abstract

The original CANDU® 600 design utilizes adjuster absorber (AA) rods to flatten the flux shape in the reactor core optimize power output, compensate for fuel burnup, provide excess reactivity to overcome 135Xe buildup following a power reduction, and allow for reactivity shim. At Point Lepreau Nuclear Generating Station (PLNGS) in 1999, adjuster absorber banks 6 and 7 were locked in the reactor core and removed from service. Later in 2019, adjuster absorber banks 1–5 were placed on manual. Since then, a significant program was put in place to restore adjuster banks 1–6 to service, which was successfully completed in October 2023. Adjuster absorber bank 7 remains locked in-core. This paper summarizes the rationale for removing the PLNGS adjuster absorbers from service, the effort required for their restoration, applicable lessons learned, and next steps.