Keywords:Fukushima daiichi, Reactor decommissioning, Strength of the containment vessel steel, Effect of temperature history, Fracture toughness
It has been indicated that the containment vessel experienced heating by melted fuels during the severe accident. Specimens of containment vessel steels and the similar alloys were heated to temperatures above the austenitizing temperature (Ac1). Tensile, fracture toughness, hardness and the microstructure of the specimens have been obtained at room temperature. Hold time during the heat treatment was within 1000 h. Specimens heated to 1000oC and cooled slowly exhibited the fracture toughness value of higher than 1000 kJ/m2 (the value is higher than that before heating). Specimens cooled rapidly, however, exhibited much smaller toughness of 150 MPam1/2. Results of the specimens heated to temperatures below Ac1 have been also obtained. Effects of temperature, aging time and cooling rate will be introduced.