QUALIFIED LIFE EXTENSION OF SAFETY RELATED ELECTRICAL EQUIPMENT

摘要

The Equipment Qualification (EQ) Group at Southern Company Services performs qualified life evaluations for safety related electrical equipment located in harsh environments. These qualified life evaluations are performed prior to each refueling outage for all safety related electrical equipment that is scheduled for replacement. The qualified life evaluations involve a review of generic qualification, temperature monitoring data, and condition monitoring data. As a result of these evaluations, qualified life extension has been achieved for most safety related electrical equipment. Qualified life is a function of thermal aging data from the generic qualification program, normal operating temperature at the equipment location, and activation energy for the weak link component in the equipment. The thermal aging time and temperature from the generic test program are fixed parameters in the qualified life analysis, but the normal operating temperature and conservative activation energies are variables. Qualified life is normally limited by thermal aging, but radiation aging and mechanical aging are also considered in the qualified life evaluation to ensure that they are not more limiting. The qualified life analysis in the generic qualification program typically assumed a normal operating temperature that would envelop most plants. However, normal operating temperatures are usually lower than the generic temperature and they can be substituted in the analysis with plant specific temperatures. Temperatures at plant specific locations were determined in the past by use of design criteria with peak summer temperatures, but seasonal data is now used from temperature monitors at plant specific locations. The results of temperature monitoring have revealed that peak temperatures are typically 10 - 20℉ cooler than design temperatures. However, it has been discovered during temperature monitoring that elevated temperatures exist on the main steam isolation valves (MSIVs). As a result, the MSIVs have been extensively surveyed to determine the actual temperatures at various component locations around the actuator. Using the survey data the EQ Group has performed qualified life evaluations, which resulted in reduced lives and more frequent replacement intervals for certain components. For high frequency replacement equipment throughout the plant a condition monitoring program is used to evaluate degradation and furtlier justify life extension. Based on the assumption that artificial aging in the original EQ test program was more severe than natural aging in the plant, the program provides degradation data that can be used for qualified life extension of the equipment. The equipment can be removed from service at the end of its qualified life and compared with known degradation amounts to determine how much additional life remains.