陽電子消滅法による原子力発電所ステンレス鋼配管の疲労評価

Abstract

Since positron annihilation lineshape analysis can evaluate the degree of fatigue damage, detecting defects such as dislocations in metals, we used the method to evaluate the degree of fatigue damage in a type 316 stainless steel pipe, which is used in the primary system of a nuclear power plant. Using 68Ge as a positron source, an energy spread of annihilation gamma ray peak from the material was measured and expressed as the S-parameter.Actual plant material cut from a surge line pipe of a pressurizer in a pressurized water type nuclear power plant was measured by positron annihilation lineshape analysis and the S-parameter was found. Comparing the S-parameter with a relationship between the S-parameter and fatigue life ratio of the type 316 stainless steel, we evaluated the degree of fatigue damage of the actual material. Furthermore, to verify the evaluation, microstructures of the actual material were investigated by TEM (transmission electron microscope) to observe dislocation densities. As a result, a change in the S-parameter of the actual material from standard as-received material (type 316 stainless steel) was in the range from −0.0013 to 0.0014, while variations in the S-parameter of the standard as-received material were about ±0.002; differences between the actual material and the as-received material were not significant. Moreover, the dislocation density of the actual plant material observed by TEM was almost the same as that of the as-received material. In conclusion, we could verify the evaluation of the positron annihilation lineshape analysis for fatigue damage.