Evaluation technique for irradiated materials using advanced positron annihilation spectroscopy method

With the increasing demand for light water reactor plant life extension, more accurate nondestructive analysis of material' degradation is required in order to evaluate the integrity of plant component materials. We have developed the advanced positron annihilation spectroscopy (PAS) method for the materials of a reactor pressure vessel (RPV), based on the conventional PAS method that has been used for the study of point defects in crystals.In the development process, the focus in terms of hardware was placed on the gamma-ray measurement system. In terms of software, the measurement procedure was carefully determined to reduce the noise level, and the evaluation parameter was properly defined based on the degradation mechanism of the material. As a result, the highest accuracy is obtained independently of the measurement conditions. This is considered to be a great advantage for nuclear reactor components, which are occasionally highly radioactive. Utilizing the new system, we analyzed the degradation of simulated model alloy of RPV steels and found that the new parameter Sf obtained by the advanced PAS method had a good correlation with the parameter obtained by the mechanically destructive test method. (author)