Status of USA reactor vessel surveillance programs

Surveillance is conducted so that radiation-induced changes to the reactor vessel materials over long (40 year) periods are monitored and can be related to the Boiler and Pressure Vessel code (ASME) safety criteria. Although other factors must be considered, the long-term structural integrity of the reactor vessel environment is of primary interest. Surveillance is defined as the periodic removal of representative specimens of reactor pressure vessel materials after exposure inside the reactor vessel at positions to simulate the service exposure of the particular vessel and the analysis of such specimens to project the condition of the reactor vessel and eventual needs for special action to ensure the continued integrity of that vessel. The nature of the data required to conduct an analysis of reactor pressure vessel surveillance programs and the factors which exert the most influence on the results include:- the properties of steels used in reactor vessels; the specification of vessel steels and their applications; selection of steel components likely to be controlling with respect to plant operation; the factors which control steel fracture; the procedures for testing propensity to fracture; rules for reactor vessel design and those for assuring reliability; reactor operating conditions, including neutron environment, and their effects on the vessel; the results of periodic assessment and reassessment of radiation effects; projection of early surveillance results for predicting future vessel performance. A summary of the surveillance data available is given. (U.K.)