Check of Master Curve application to embrittled RPVs of WWER type reactors

Abstract

Lifetime of reactor pressure vessels is practically determined by their resistance against potential brittle/non-ductile failure. This resistance is then governed by the damaging effect of neutron embrittlement. Integrity assessment of reactor pressure vessels has been changed and improved during several past decades but it still contains some parameters which were introduced historically and are still being used. Representative of such parameters is Charpy notch impact testing and resulting transition temperature determination. Even though this test has technological origin, it is still used in material acceptance tests and also practically in most of surveillance specimens programmes for determination of radiation damage level. Vast application of fracture mechanics to reactor pressure vessels integrity assessment have also brought a tendency for finding a correlation between results of Charpy notch impact tests and fracture mechanics parameters - results are usually called "design fracture toughness curves". Contraversion between Charpy impact tests and fracture mechanics use for RPV integrity assessment can be overrun by direct use of static fracture toughness data obtained from surveillance, e.g. using a specimen reconstitution technique and consequently a "Master Curve" approach. Discussion on the use of real fracture toughness data for integrity assessment of WWER type RPVs is given together with a comparison with results from a standard assessment method using design fracture toughness curves based on Charpy impact data.