Nobuo Totsuka

Influence of Dissolved Hydrogen on Structure of Oxide Film on Alloy 600 Formed in Primary Water of Pressurized Water Reactors

In order to investigate the relationship between the susceptibility of primary water stress corrosion cracking (PWSCC) in Alloy 600 and the content of dissolved hydrogen (DH) in the primary water of pressurized water reactors (PWR), structural analysis of oxide films formed under four different DH conditions in simulated primary water of PWR was carried out using a grazing incidence X-ray diffractometer (GIXRD), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). In particular, to perform accurate analysis of the thin oxide films, the synchrotron radiation of SPring-8 was used for GIXRD. It has been observed that the oxide film is mainly composed of nickel oxide, under the condition without hydrogen. On the other hand, needle-like oxides are formed at 1.0 ppm of DH. In the environment of 2.75 ppm of DH, the oxide film has thin spinel structures. From these results and phase diagram consideration, the condition around 1.0 ppm of DH corresponds to the boundary between stable NiO and spinel oxides, and also to the peak range of PWSCC susceptibility. This suggests that the boundary between NiO and spinel oxides may affect the SCC susceptibility.

Influence of interaction between multiple cracks on stress corrosion crack propagation

Abstract The interaction between multiple cracks has a major influence on crack growth behaviours. This influence is particularly significant in stress corrosion cracking (SCC) because of the relatively large number of cracks initiated due to environmental effects. In the SCC experiments using alloy 600 in high-temperature environments, many cracks were observed on the surface of fractured specimens. In this study, the interaction between multiple cracks was evaluated using a crack growth simulation. Some improvements were made to the simulation to reduce the calculation loads, which made it possible to conduct the simulation for many cases. Through the simulation, the relationships between the interaction and relative position, relative length, etc. of cracks were examined. The influence of the interaction between multiple cracks on the experimental results is then discussed.

Influence of Dissolved Hydrogen on Oxide Film and PWSCC of Alloy 600 in PWR Primary Water

In order to investigate the influence of dissolved hydrogen on the oxide film and primary water stress corrosion cracking (PWSCC) of Alloy 600 in primary water of PWR under actual operating temperature range, electrochemical polarization measurement, analysis of the oxide film on the alloy and PWSCC test were carried out. In all cases, the content of dissolved hydrogen was changed from 0 to 45 cc/kg H2O. The anodic polarization curve reveals that the peak current density increases with increasing dissolved hydrogen and the change of the peak current density becomes maximum between 11 and 30 cc/kg H2O of dissolved hydrogen. According to the results of oxide film analysis, it is seen that the oxide films formed below 11 cc/kg H2O of dissolved hydrogen are relatively thick and rich in Ni, but those formed at higher dissolved hydrogen content are relatively thin and rich in Cr and Fe. The susceptibility of the alloy to PWSCC has a peak at 11 cc/kg H2O of dissolved hydrogen, which reveals that the property of the oxide film may play important role in PWSCC of alloy.

Effect of Strain Rate on Primary Water Stress Corrosion Cracking Fracture Mode and Crack Growth Rate of Nickel Alloy and Austenitic Stainless Steel

Abstract The primary water stress corrosion cracking (PWSCC) of Alloy 600 (UNS N06600), Type 304 (UNS S30400), and Type 316 (UNS S31600) stainless steels (SS) was studied at 360°C and at nominal st...

Development of an autoclave with zirconia windows for in-situ observation of sample surface under the primary water conditions of pressurized water reactors

In some cases in-situ observation of sample surface is desirable for the corrosion research of reactor materials under the conditions of primary water of light water reactors. For the primary water conditions of boiling water reactors (BWR), sapphire crystal is used for an observation window of such autoclaves. 1,2) But in the primary water of pressurized water reactors (PWR), boric acid blurs sapphire crystal surface and prevents from thein-situ observation of sample surface. In order to find a possibility to observe sample surface of reactor materials under the primary water conditions of PWR and to develop an autoclave with such function, the following procedures were carried out: (1) A search of observation window materials which can be used under the primary water conditions of PWR. (2) Proposal of yttria stabilized zirconium oxide (cubic zirconia, CZ) crystal as a possible candidate for this purpose. (We chose CZ, because sintered zirconia had been widely utilized as an excellent electric insulator in the primary water condition.) (3) Measurement of light transmissivity of CZ and sapphire crystals after immersion in the water with the conditions of PWR. (4) Development of an autoclave with CZ windows for the in-situ observation of sample surface under the primary water conditions of PWR.

Transgranular Stress Corrosion Cracking of Mild Steel in 0.5N H2SO4 + 0.005N KI Solution – Stress Corrosion Behavior Under Constant Crosshead Speed Test

Abstract Investigation of stress corrosion cracking (SCC) of mild steel in 0.5N H2SO4 + 0.005N KI was carried out using a constant crosshead speed method at room temperature. Smooth specimens teste...

Transgranular Stress Corrosion Cracking of Mild Steel in 0.5N H2SO4 + 0.005N Kl Solution – XPS Observation of the Surface Film

Abstract The surface film formed on strained mild steel in 0.5N H2SO4 containing 0.005N Kl was examined by XPS in connection with the SCC susceptibility which is highest around 0.06 V relative to the corrosion potential. The film was found to consist mainly of FeOOH containing small amounts of sulfur and iodide. The iodide content alone varied with the polarization potential and had a critical potential coinciding with that for the SCC susceptibility, which is explained by the instability of the surface film at the potential.