STUDY ON LIFE EXTENSION OF AGED RPV MATERIAL BASED ON PROBABILISTIC FRACTURE-MECHANICS - JAPANESE ROUND-ROBIN

This paper is concerned with round-robin analyses of probabilistic fra cture mechanics (PFM) problems of aged RPV material Analyzed here is a plate with a semi-elliptical surface crack subjected to various cycli c tensile and bending stresses. A depth and an aspect ratio of the sur face crack are assumed to be probabilistic variables. Failure probabil ities are calculated using the Monte Carlo methods with the importance sampling or the stratified sampling techniques. Material properties a re chosen from the Marshall report, the ASME Code Section XI, and the experiments on a Japanese RPV material carried out by the Life Evaluat ion (LE) subcommittee of the Japan Welding Engineering Society (JWES), while loads are determined referring to design loading conditions of pressurized water reactors (PWR). Seven organizations participate in t his study. At first, the procedures for obtaining reliable PFM solutio ns with low failure probabilities are examined by solving a unique pro blem with seven computer programs. The seven solutions agree very well with one another, i.e., by a factor of 2 to 5 in failure probabilitie s. Next sensitivity analyses are performed by varying fracture toughne ss values, loading conditions, and pre and in-service inspections. Fin ally, life extension simulations based on the PFM analyses are perform ed It is clearly demonstrated from these analyses that failure probabi lities are so sensitive to the change of fracture toughness values tha t the degree of neutron irradiation significantly influences the judgm ent of plant life extension.