Abstract: This invention provides austenitic steel having a superior resistance to neutron irradiation, a nuclear reactor and a nuclear fission reactor using such steel.In the present invention, austenitic steel containing at least one of Pd and Pt is used for a member which undergoes neutron irradiation in high-temperature water. More specifically, the steel consists essentially of not more than 0.02% C, not more than 1% Si, 0.5-15% Mn, 9-26% Cr, 8-20% Ni, 0.5-3% Mo, at least one kind of 0.1-16% selected from the group consisting of Pd and Pt, and not less than 50% Fe, and may further contain not more than 1.0% of at least one kind selected from the group consisting of Nb, Ti, Zr, Hf and V, and this is used for structural members in a core of a nuclear reactor and a nuclear fission reactor.

Abstract: A method and an apparatus for estimating the remaining service life of an object by measuring the physical quantity of a sample and which are applicable to a nuclear reactor. A plurality of model samples are experimentally prepared by preliminarily disposing a material having substantially the same composition as the object to be subjected to the estimation in an environment substantially the same as the object and measuring the physical quantities of the model samples in relation with exposure times. From this experiment, a relationship between the exposure time and the physical quantity under such an environment is obtained. Further, a critical exposure time which will cause an unstable fracture of a material of an actual sample, which is made of a material substantially the same as the object and placed in substantially the same environment as the object, is preliminarily obtained from the relationship between the exposure time and the physical quantity for the model samples.

Abstract: A welded structure and a method for making same wherein a plurality of weld metals, such as martensitic steel and austenitic steel, differing in coefficient of thermal expansion from each other are deposited in a plurality of layers thicknesswise of the welded structure in a gap defined by structural members to be welded in such a manner that a layer of the weld metal of higher coefficient of thermal expansion is covered by a layer of the weld metal of lower coefficient of thermal expansion in a weld formed, to improve brittle fracture strength, fatigue strength and stress corrosion cracking resistance of the weld. By subjecting the welded structure to stress relief annealing treatment, it is possible to produce compressive stress on the surface of the layer of the weld metal of lower coefficient of thermal expansion.