ROLE OF IRRADIATED MATERIALS DATA IN PERFORMING REACTOR VESSEL FRACTURE-TOUGHNESS ANALYSIS

The role of surveillance materials data in the various reactor vessel fracture toughness analyses required to insure that the vessels operat e in accordance with defined regulations is often overlooked, because of the apparent prescriptive approaches that are used to perform the e valuations. These procedures are normally so conservative that, as the reactor vessel ages, the restrictions severely limit plant operation. A unique and often unrecognized feature of the regulatory guide provi des for the use of surveillance data. This feature permits the plant t o obtain credit for having a viable surveillance program. The role of irradiated materials data is significant in the evaluation of three ph ases of reactor vessel operation or evaluation. These phases are as fo llows: normal operating pressure-temperature limits; evaluation of pre ssurized thermal shock; the case of a low Charpy upper shelf energy. T he significance of having reliable irradiated fracture toughness data and their role in each of these evaluations are discussed. Data on irr adiated material fracture toughness properties from reactor vessel sur veillance programs improve the operating limitations of reactor vessel s. These data permit the reduction of conservatisms applied when mater ial-specific data are not available. The rewards of greater operating flexibility are sufficient that they encourage plant operators to main tain the optimum surveillance program for their reactor vessel.