J sub(IC) fracture toughness of nuclear reactor pressure vessel steels in transition and upper shelf regions

The J sub(IC) fracture toughness of the nuclear reactor pressure vessel steel and its heat-treated steel, which was simulated to one embrittled by the neutron irradiation, has been evaluated by the electrical potential method in the range from transition to upper shelf regions. The results obtained are summarized as follows: (1) The difference of transition temperatures between as received and heat treated steels at 41 J of absorbed energy in Charpy V-notch impact (CVN) test is nearly the same as the temperature shift of 100 MPa√m level in the fracture toughness, regardless of the specimen size at the transition region. (2) At upper shelf region, the percent decrease of the fracture toughness is much more than that of the CVN absorbed energy. (3) From the fact mentioned above, it is proposed to use two test methods as the new surveillance test practice. One is the CVN test for the transition region, and another is the J sub(IC) fracture toughness test for the upper shelf region. (4) The electrical potential method can be the candidate technique to detect the onset of crack initiation for the irradiated material in the J sub(IC) test from the view point of less specimen and technical difficulty. (author)