In this research, to investigate the persistence of compressive stress on a shot peened surface, the residual stresses in a multi-pass welded pipe joint after shot peening were analyzed. Then, the variation of the stress distribution in the welded pipe was examined by elastic plastic analyses under axial tension and compression with consideration of the shot peened residual stress distribution. As a result, it was found that the stress distribution remains in compression by applying tension followed by compression. It was also found that the compressive stress can decrease by applying compression followed by tension. From the above results, it can be said that the persistence of compressive stress due to shot peening should be discussed before the peening operation, especially a large load can be assumed to act on the shot peened part.

Gas sampling type sodium small leak detector, SID (Sodium Ionization Detector), a gas sampling detector installed to monitor small sodium leak in the Prototype Fast Breeder Reactor Monju, had been operated since its system start-up test through to the 40% reactor’s output test. It’s use was terminated in April, 2018. SID showed some indication variations during its operation period, and necessary measures were implemented. As a result, the SID system maintained its functions without any critical malfunction until the end of its operation.

Flow-accelerated corrosion (FAC) causes a wide range of pipe wall thinning, and there is a risk that serious accidents are caused by significant pipe rupture and coolant leakage due to FAC. The purpose of this paper is to specify what kind of turbulence parameters affects wall thinning rate and to evaluate the influence of frequency characteristics of velocity fluctuations on wall thinning rate by conducting an accelerated wall thinning test using benzoic acid as thinning wall and a flow visualization test using sodium iodide solution and acrylic channel. Benzoic acid can simulate wall thinning of carbon steel in terms of mass transfer in high Schmidt number flow, and flow visualization was conducted by particle image velocimetry (PIV). From the evaluation of frequency characteristics of velocity fluctuation, it was found that the characteristic could not explain how large the wall thinning rate was. After scrutinizing the correlation between wall thinning rates and turbulent quantities, it was found that the total shear stresses composed of contribution by molecular viscosity and Reynolds stress evaluated not on and in the vicinity of the wall but also far from the wall have much to do with the wall thinning rate. In addition, the profile of the total shear stress to the power of 0.25 corresponds with that of wall thinning rate reasonably well.

This paper describes a three-dimensional environment reconstruction obtained from multiple images, aiming to determine the status of the reactor building of Fukushima Daiichi Nuclear Power Station. The Structure from Motion was used to estimate the three-dimensional structure of the objects and camera trajectory. To improve the feature detection achieved using the Structure from Motion, a contrast enhancement filter and unsharp masking filter were applied to pre-process the images. We applied the Structure from Motion method to pre-process multiple images obtained by reconnaissance inside the Primary Containment Vessel of Unit 3 using a remotely operated vehicle. Moreover, to improve the visibility, a Multi-View Stereo technique was applied to the data generated using the Structure from Motion. Herein, we report the results of the three-dimensional environment reconstruction.

Chubu electric power (Chubu) is now under investigation of radiation effects on the reactor pressure vessel (RPV) steel of a decommissioning BWR-4 in the Hamaoka unit-1 plant to confirm the validity of the current maintenance methodology and resultantly safety tolerance up to now. As a part of this program, we planned to survey the irradiation responses of the base metal just beneath the inner cladding of RPV. In this paper we report the results of Charpy impact and fracture toughness tests of a mock-up block of the archive material of RPV. The impact test using 1/3 sized specimens showed that the ductile brittle transition temperature (DBTT) of the base metal and cladding-HAZ (heat affected zone) were almost same, and the difference in the upper shelf energy (USE) between base metal and cladding-HAZ is within a scatter band. Fracture toughness test using compact tension (CT) specimens are successfully done and the results were compared with that in literature. Our data set of fracture toughness are considered to be consistent with a temperature dependent curve composed of past data.