THE J-RESISTANCE CURVE LEAK-BEFORE-BREAK TEST PROGRAM ON MATERIAL FOR THE DARLINGTON NUCLEAR GENERATING-STATION

The Darlington Leak-Before-Break (DLBB) approach has been developed for large diameter (21, 22, 24 inch) SA106B heat transport (HT) piping and SA105 fittings as a design alternative to pipewhip restraints and in recognition of the questionable benefits of providing such restraints. Ontario Hydro's DLBB approach is based on the elastic plastic fracture mechanics (EPFM) method. In this test program, J-resistance curves were determined from actual pipe heats that were used in the construction of the Darlington heat transport systems (Units 1 and 2). Test results showed that all pipes, welds and heat-affected zone materials within the scope of the DLBB program exhibited uppershelf toughness behavior. All specimens showed high crack initiation toughness, rising J-resistance curve and stable and ductile crack extension. Toughness of product forms depended on the direction of crack extension.