Many efforts are currently devoted to the development of soft-computing diagnostic tools. Within these efforts, the present work illustrates the application of a fuzzy logic system approach to fault classification in the case of single and multiple failures of different intensity. The approach bears the great advantage that the identification task does not rely on an explicit mathematical model of the behavior of the monitored plant, the if-then rules of the fuzzy classification model being inferred from available preclassified signal data. A case study is presented regarding the classification of faults in the gland seal system of a pump of the primary heat transport system in a pressurized heavy water reactor, Canada deuterium uranium 6.