To ensure integrity of structures and components in nuclear power plants, the demand has been increased for establishing nondestructive method for detection of pre-existing plastic strain. In this study, we examined applicability of potentiostatic etching method, which developed in our past paper, for actual austenitic steel components. On etching condition, solution temperature is one of the critical parameter. Thus this method should be conducted at a constant temperature between 30°C -40°C. Using r...
英字タイトル:
Applicability of potentiostatic etching method for evaluation of plastic strain in austenitic stainless steel structure

Since the Great Eastern Japan Earthquake, the most important issue that we have to face in reconstruction and local renewal is the safe decommissioning of Tokyo Electric Power Company's Fukushima Daiichi nuclear power plant reactors. Tohoku University is one of the first institutions to formulate diverse recovery projects in order to support the resolution of various difficulties that materialized after the disaster. One of these pillar projects that the university has undertaken is the Reactor Decommi...
英字タイトル:
Current status in Tohoku University fundamental research on nuclear decommissioning and human resources development project

1.はじめに 平成 23 年に発生した東京電力株式会社福島第一原子 力発電所の事故から約 6 年が経過した現在、今後 30 年 以上の長期に亘ることが予想されている同発電所 1 ~ 4 号機の廃止措置は、国家の威信を賭けた大事業として政 府を筆頭とするオールジャパン体制で中長期ロードマッ プ [1] に基づき、懸命な努力がなされている。この世界 にも前例の無い大きな課題(技術的挑戦)を解決し、廃 止措置を安全かつ着実に進めていくには、我が国の関連 組織の総力を挙げた取組みが必要となっている。 このような中......

Pipe wall thinning is one of the important degradation phenomena taking place in the nuclear power plant. Major mechanism of the mainly pipe wall thinning is Flow Accelerated Corrosion (FAC), where chemical process plays the primary role. But mechanism of FAC is not yet full y understood. Especially characteristics of oxide film formed in FAC is not well known although oxide film property would be strongly related to thinning rate in FAC. The main objective of this work is finding characteristics of oxide ...
英字タイトル:
Relation of Thinning Rate and Characterization of The Oxide Film Formed in Flow Accelerated Corrosion of Carbon Steels

In May 2011, at Hamaoka-5, the main condenser thin tube was damaged and seawater intruded to the reactor facility. It was purified to a level where corrosion did not occur by replacing the intruding water. However a few years later, the leak occurred from the stainless steel welded joint. It is presumed that the cause is that crevice corrosion was caused by the welded part of stainless steel with high corrosion sensitivity, the inflow of chloride ions, and the crud deposits. And in this study, we aim to elu...
英字タイトル:
Elucidating the corrosion of the stainless steel welded joint caused by seawater intrusion at Hamaoka-5

Wet polish with fine emery paper is most commonly used for final finish of SCC specimens and corrosion coupons. Although cold w ork introduced by the fine emery finish is slight, a series of experiments have demonstrated that the very slight cold work can ffect oxidation behaviors and apparent SCC susceptibility of Ni base alloys in hydrogenated steam. Oxidation tests and reverse type SCC experiments have been done in hydrogenated steam at 400C for Ni-Cr binary alloys with various Cr content from 14% t o 3...
英字タイトル:
Effect of slight cold work introduced with fine emery finish on oxidation and cracking behaviours of Ni base alloys in hydrogenated steam

Corrosion rate of carbon steel SS400 was investigated in test solution (NaClaq, Cl-:200ppm) with a rotating cylinder electrode system. Polarization resistance measurement was used to determine variation of corrosion rate with time and specimens surface were observed after the measurements. Under aerated condition (dissolved oxygen: 7.3ppm), the corrosion rate increased with increasing rotating speed in low rotation speed ranges , but the corrosion rate decreased in high rotating speed ranges. The reas...
英字タイトル:
Evaluation of corrosion of cooling system piping of Fukushima Daiichi NPP

It was reported that nitride layer formed on SUS310S heating tubes in the reactor of melamine production plant showed severe spalling susceptibility. After replacement to SUS304heating tubes, spalling and thinning was suppressed. According to previous studies, a crystal structure of the nitrided layers of SUS310S and SUS304 heating tubes mainly consist of γ’ and α’, respectively. The reason why the SUS304 heating tube showed low spalling susceptibility was considered to be a smaller expansion rate of α...
英字タイトル:
Wastage mechanism of heating tubes made of austenitic stainless steels in a complex environment of nitriding, oxidizing, and carburizing

The core shroud specimens (316L stainless steel) were used to characterize the surface hardening layer introduced by machining and to evaluate the SCC susceptibility in the simulated BWR coolant environment. Based on the results obtained, the effect of the surface hardening layer on the SCC susceptibility and its mechanism are discussed. It is suggested that the wall part has clearly higher SCC susceptibility than the support ring part when compared between the as-received materials (with surface hardening ...
英字タイトル:
Evaluation of SCC susceptibility of austenitic stainless steel with surface hardening layer in high-temperature water

In this study, we investigate the effect of oxygen potential on oxide film, intergranular oxidation and cracking susceptibility on nickel base alloy in hydrogenated superheated steam at 400℃. Intergranular cracking occurred at oxygen potential of LOGPO2=-26.32(Ni/NiO equilibrium). In contrast, no cracking occurred at oxygen potential of LOGPO2=-24.09 and LOGPO2=-27.04(near the cracked condition). This result shows that oxygen potential range for cracking susceptibility seemed to be narrow in hydrogenat...
英字タイトル:
Effect of oxygen potential on oxide film, intergranular oxidation and cracking susceptibility on nickel base alloy in superheated steam