NTD system prevents catastrophic failures

Many nuclear power plant main coolant pumps are instrumented with on-line monitoring systems. These systems use proximity probes and velocity pickups mounted on the motor housings. With a threshold sensitivity of 25% loss of local diameter, on-line systems are capable of preventing catastrophic failures. However, indications of deteriorating shaft structural condition may not be early enough to support orderly, planned replacement of shafts. Monitored shafts removed before failure occurs have contained transverse cracks measuring up to 75% of local shaft diameter. There is a need for a technology that would permit in-situ non-destructive testing (NTD) of pump shafts. The test is based upon an innovative application of modal analysis. The technique involves performing a static, in-situ modal survey of the rotor system and then comparing the measured high order natural frequencies to those predicted by an analytical model. Differences can be related to a defined loss of cross sectional area