Indications of Ultrasonic Testing (UT) of 4 weld joints in Primary Loop Recirculation (PLR) piping in Hamaoka unit-2 had been identified during the 20th outage (2004). Metallurgical investigation after cutting from 2 weld joins had been conducted because of its accessibility etc. The 4 weld joins had been welded at the plant construction (1978), operated and IHSI (Induction Heat Stress Improvement) had been performed during the 1st outage (1979). 25 years passed by until the metallurgical investigation. As a result of the investigation, crack growth retardation by the IHSI was confirmed since crack tip was round and plastically deformed.