LIFE EXTENSION SIMULATION OF AGED REACTOR PRESSURE-VESSEL MATERIAL USING PROBABILISTIC FRACTURE-MECHANICS ANALYSIS ON A MASSIVELY-PARALLEL COMPUTER

This paper describes a probabilistic fracture mechanics (PFM) computer program using the parallel Monte Carlo (MC) algorithm. In the stratif ied MC algorithm, a sampling space of probabilistic variables such as fracture toughness value, the depth and aspect ratio of an initial sem i-elliptical surface crack is divided into a number of small cells. Fa tigue crack growth simulations and failure judgements of those samples are performed cell by cell in parallel. The developed PFM program is implemented on a massively parallel computer composed of 512 processor s. As an example, some life extension simulations of aged reactor pres sure vessel material are performed, taking analysis conditions of norm al and upset operations of PWRs. The results show that cumulative brea kage probabilities of the analyzed model are of an order of 10(-7) (1/ crack), and that parallel performance always exceeds 90% owing to an e mployed function of dynamic workload balancing. It is also demonstrate d that the degradation of fracture toughness values due to neutron irr adiation and the probabilistic variation of fracture toughness values significantly influence failure probabilities.