Expansion of high temperature creep test data for failure evaluation of BWR lower head in a severe accident

Abstract

Since the Fukushima Daiichi nuclear power plant accident, we have been developing a failure evaluation method that considers creep damage mechanisms for the early completion of the decommissioning of the nuclear power plants. The method evaluates failure of the lower head using a detailed three-dimensional finite element analysis (FEA) model of the lower head, including penetration, stub tubes, and weld parts. For the FEA, we have been obtaining material properties for which no data are provided in existing databases or in the literature. In particular, creep data corresponding to the high temperature region near the melting point of materials is important in evaluating creep deformation under severe accident conditions. In this study, we obtained the uniaxial tensile and creep properties for low-alloy steel, Ni-based alloy, and stainless steel. In particular, creep test data with long rupture times at high temperatures are expanded using a tensile test machine that can measure the elongation of test specimens in a noncontact measurement system. The parameters related to the failure evaluation were improved on the basis of the expanded creep database.