Robust PCI monitoring during PWR operation at Southern Nuclear

Emerging industry practice is transitioning from global ramp rate monitoring to local power monitoring for PCI concerns. In consideration of these changes, Southern Nuclear has worked with Studsvik and the UK National Nuclear Laboratory (NNL) to evaluate more robust PCI monitoring capabilities during plant operation. Using Studsvik's automated reactivity management system, CMSOps and NNL's fuel performance code, ENIGMA, an actual operational event from one of Southern's PWRs was evaluated using several PCI methodologies. This study was of particular interest since there was an indication of leaking fuel within 24 hours of the event described herein. The methodologies applied in evaluating this event range from simplistic calculations of changes in nodal linear heat generation rates, to explicit individual pin-by-pin thermo-mechanical fuel performance assessment. The merits and deficiencies of the various methods are presented. The clear choice is the coupled CMS to ENGIMA capability, termed ONUS. In the case evaluated here for Southern Nuclear, the analyses confirmed that the fuel failure mechanism was not due to classical PCI, thereby, allowing the utility to eliminate this mechanism from further investigation.