Evaluation of neutron irradiation embrittlement of heavy section nuclear reactor pressure vessel steels in terms of elastic-plastic fracture toughness

Abstract

The fracture toughness degradation due to neutron irradiation was examined for the evaluation of the structural integrity of a nuclear reactor pressure vessel using four kinds of currently used heavy section manganese-molybdenum-nickel low alloy steels, which included the welded joint as well as the base metal. Neutron irradiation was conducted up to 2to 7×10 19 n/cm 2 > 1 MeV at 290°C in JMTR, and the embrittlement was mainly evaluated by the Charpy and fracture toughness tests using small three point bend specimens. From the results, the following can be pointed out: 1. (1) The elevations of the transition temperature of steels used, which are evaluated by 41 J of the Charpy absorbed energy, are within 50°C, and a quite high resistance against neutron irradiation embrittlement is observed. 2. (2) The J IC fracture toughness and J - R curve of irradiated materials as well as unirradiated ones are successfully determined by a dc electrical potential method using a single specimen. 3. (3) At the transition region, the increase of transition temperature (ΔRT NDT) at the 41 J level of the Charpy impact test is nearly equal to the shift at the 100 MPa m 1 2 level of the fracture toughness test.