An Approach to Aging Management Verification for Safety Analysis

Abstract

The Deterministic Safety Analysis group at Point Lepreau Nuclear Generating Station developed a process that identifies the operational parameters used in safety analysis that are impacted by aging effects, and predicts when their margins to the safe operating envelope (SOE) are at risk. Operating with margins too low or too high can negatively impact the economics or safety requirements of plant operations. These age-related safety analysis parameters included header temperatures and pressures, channel flows, pressurizer level, and pressure tube diametral creep. This process involves trending station data over time for those parameters, applying a 95% prediction interval to account for uncertainty and variability of the data, and comparing it to the surveillance limits (SL) and safety analysis limits (SAL). The results show both an increase and decrease in margin to the SL and SAL over time depending on the parameter. Although each parameter trends differently, this process allows the DSA group to verify that the station will continue to operate within the SOE over time and to identify which trends may have a negative impact on margin. This information will allow the DSA group and station operations to identify future margin issues and pro-actively plan analyses and develop mitigating techniques and strategies to address them before they become challenges to operation.