PTS EVALUATION CASE STUDY CONSIDERING ACTUAL THROUGH-WALL FRACTURE TOUGHNESS DISTRIBUTION

摘要

The surveillance test specified in JEAC4201 requires the fracture toughness evaluation of base metal at I/4-T thickness and T-L orientation, where the initial fracture toughness generally is the minimum in whole thickness at any orientation. In the present study, actual through-wall fracture toughness distribution from a commercial RPV base metal on both of T-L and L-S (actual through crack orientation) orientations were evaluated from Zion Unit 1, which was decommissioned after 25 years (I5EFPY) commercial operation. A base metal block of 40mm(T) x 216mm(L) x 216mm(S) was retrieved from belt line region by effort of ORNL and provided to CRIEPI under the USA - Japan collaborative agreement on civil nuclear research framework called CNWG. Through-wall fracture toughness distiibution was characterized by means of the Master Curve method utilized by 4mm thickness C(T) "Mini-C(T) " specimens. Near surface material possessed significantly high fracture toughness at amount of 40 degrees Celsius lower reference temperature (T_o) than those in center thickness locations, despite of higher neutron fluence gained during service operation. Pressurized thermal shock evaluation by probabilistic fracture mechanics code PASCAL4 demonstrated that through-wall fracture probability can be remarkably lowered by considering through-wall fracture toughness distribution.