DEFECT ASSESSMENT BENCHMARK STUDIES

Assessments of the resistance to fast fracture of the beltline region of a PWR vessel subjected to a pressurized thermal shock (PTS) transie nt have been carried out using the procedures of French (RCC-M) and Ge rman (KTA) design codes, and comparisons made with results obtained us ing the R6 procedure as applied for Sizewell B. The example chosen for these comparisons is of a generic nature, and is taken as the PTS ide ntified by the Hirsch addendum to the Second Marshall report (1987) as the most servere transient with regard to vessel integrity All assess ment methods show the beltline region of the vessel to be safe from th e risk of fast fracture, but by varying factors of safety. These facto rs are discussed in terms of margins between limiting and reference de fect sizes, fracture toughness and stress intensity factor, and materi al temperature and temperature at the onset of upper-shelf materials b ehaviour. Based on these studies, consideration is given to issues inv olved in the harmonization of those sections of the design codes which are concerned with methods for the demonstration of the avoidance of the risk of failure by fast fracture.