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概要

In Japan, the preventive maintenance task of the 600 series nickel basis alloy weld of the reactor vessel (RV) and the steam generator (S/G) safe end weld are pushed forward sequentially, and a defect sizing using the ultrasonic testing (UT) from the inside of the safe end is carried out when the defect was dete cted by surface inspection prior to the work. Some defects are recognized on the S/G safe end and the R/V safe end in Japan, and these defects have occurred in the axial direction of the safe end weld. Therefore the defect sizing by UT arranges a probe on the direct top of the welding and inspects it, and the at tenuation of the ultrasonic wave by the welding and influence of being scattered are big, so advanced defect sizing technique for these area is required.This report shows the development status that aimed at the advancement of the sizing technique from the inside for the safe end weld. We have developed the adva nced technique using phased array UT and planned improvement of the sizing accuracy. The UT simulation technology also applied to probe development, and the optimization of the design parameter has been performed. We will apply the developed technology and carry forward safe end maintenance work in future. 1. 緒言

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