We verified that eddy current testing (ECT) has enough detectability for a welded part position of in-core monitor (ICM) housing outside and defects on a heat affected zone (HAZ) in welding of the inner surfaces for a special inspection involved in long-term operation. It is difficult to determine an appropriate inspection area if an actual welded position of an ICM housing is different from a designed position. It is presumed that detectability of ECT is decreased because a HAZ of an ICM housing inner surface is deformed by welding. We conducted a full-scale mock-up test using a simulated ICM housing specimen with a welded part and an ECT system which consisted of a welded part detection probe, a rotational ECT probe and probe moving equipment and confirmed that the ECT detected a welded part position of outside and defects of about 0.5 mm in depth despite existences of inner surface deformations of approximately 1 mm.

Failure probability of static components is used for assessing plant safety or resilience index of nuclear power plants. In this study, a failure probability assessment model was developed that considers the effect of material degradation caused by low-cycle fatigue. Crack initiation due to fatigue damage was assumed and its depth was determined from the magnitude of fatigue damage. Then, crack growth was predicted for seismic loads consisting of a main earthquake and aftershocks. Finally, the failure probability was calculated for the seismic load of various magnitudes. The model was successfully applied to a pipe of the residual heat removal system of a pressurized water reactor power plant. It was shown that the failure probability was hardly affected by the degree of fatigue damage. Although the crack depth had little influence on the fracture strength of the cracked pipe, an increase in the number of aftershocks could increase the probability of leakage.

Non-destructive evaluation technique was developed for embedded hardware using hammering inspection with AE (Acoustic Emission) sensor. The integrity of the embedded hardware is judged from both the vibration duration of the embedded hardware recorded by the AE sensor and the frequency analysis of the vibration signal. Mockup tests were carried out in order to verify the effectiveness of the technique and to obtain the diagnostic criteria. The technique was then applied to the field inspection.

Digital hammering inspection system with AE (Acoustic Emission) sensor has been developed and the effects of state, stiffness, etc. on the natural frequency of metal and concrete objects to be inspected were evaluated in terms of improper installations and age-related degradations. The system has been widely applied to social infrastructural diagnosis including expressways (West Nippon Expressway Company Limited, NEXCO-WEST), nuclear power plants (ex. Chubu Electric Power Co., Inc.), reprocessing plant of spent nuclear fuel (Japan Nuclear Fuel Limited) and a successful on-site trial of a new technology of i-Construction led by MLIT (the Ministry of Land, Infrastructure, Transport and Tourism).

In order to pursue safety and efficiently manage resources, we are improving our maintenance business process　by using information technology (IT) and introducing a work management process (WM process). These efforts have resulted in improvements in managing the duration of safety-equipment unavailability and in addressing non-conformance backlogs.

Safety management technology of hydrogen gas is extremely important not only for nuclear power generation but also for future society. This is international research and development on hydrogen safety technology in which industry, government and academia collaborate. A brand-new passive autocatalytic recombiner (PAR) system utilizing the monolithic “intelligent catalyst” has been studied for the long-term storage of high-concentration radioactive materials related to the decommissioning of nuclear reactors. In a small lab scale test, it was found that this monolithic catalyst can start a hydrogen oxidation reaction from a low temperature of minus 20 ℃. The monolith-type automotive catalyst showed high hydrogen conversion activity from a room temperature in a large-scale reactor of REKO-4 in Jülich (FZJ). It became clear that natural convection by reaction is greatly improved by roughening the cell density of the monolith catalyst especially under static environmental conditions such as in a storage container. Furthermore, this natural convection is strengthened by adopting a chimney, and the hydrogen oxidation reaction per unit time has improved about three times. Taking advantage of this superior catalytic property, we aim to complete the safety technology for storage containers at an early stage and advance the development of highly active catalyst from further low temperature.