(A) study on development of a rule based expert system for steam generator life extension

Abstract

The need of predicting the integrity of the steam generator(SG) tubes and environmental conditions that affect their integrity is growing to secure nuclear power plant(NPP) safety and enhance plant availability. To achieve their objectives it is important to diagnose the integrity of the SG tubes. An expert system called FEMODES(failure mode diagnosis expert system) has been developed for diagnosis of such tube degradation phenomena as denting, intergranular attack(IGA) and stress corrosion cracking(SCC) in the secondary side of the SG. It is possible with use of FEMODES to estimate possibilities of SG tube degradation and diagnosis environmental conditions that influence such tube degradation. The method of certainty factor theory(CFT) and the rule based backward reasoning inference strategy are used to develop FEMODES. The information required for diagnosis is acquired from SG tube degradation experiences of two local reference plants, some limited oversea plants and technical reports/research papers about such tube degradation. Overall results estimated with use of FEMODES are in reasonable agreement with actual SG tube degradation. Some discrepancy observed in several estimated values of SG tube degradation appears to be due to insufficient heuristic knowledge for knowledge data base of FEMODES.