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

Abstract

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.

Microstructural Characterization of SCC Crack Tip and Oxide Film for SUS 316 Stainless Steel in Simulated PWR Primary Water at 320.DEG.C.

“…This result is consistent with the oxide film formed on the nickel-based alloy under the same condition as the present authors reported previously. 26) The material used in this study was 316SS, which differs from 304SS primarily in that molybdenum is added to the former to reduce corrosion. For this reason, it was thought that molybdenum might play an important role in corrosion resistance by protecting the oxide film.…”

Effects of Hydrogen Peroxide on Corrosion of Stainless Steel, (V) Characterization of Oxide Film with Multilateral Surface Analyses

“…Furthermore, cross-sectional images and chemical compositions were observed with a scanning transmission electron microscope using energy dispersive X-ray spectroscopy (STEM-EDS). 19) Some results from X-ray diffraction (XRD), the Rutherford back scattering spectroscope (RBS) and the X-ray photoelectron spectroscope (XPS) were shown previously.…”

“…19) Then the cross-sections of oxide films were observed by scanning transmission electron microscope (STEM) and energy dispersive X-ray spectroscope (EDS).…”

Development of a microfluidic setup to study the corrosion product deposition in accelerated flow regions

“…[8][9][10][11][12] Typical PWR conditions are 295-325°C, <0.01 ppm O 2 , 2-3 ppm H 2 , 1-40 µS/cm, pH300°C 7-7.4, 0.1-3.5 ppm Li, and 0-2300 ppm H 3 BO 3 . 13 The deposition of CRUD can also occur in the secondary circuit of the PWR, operating at lower temperatures (T < 288°C) and different water chemistry (5 ppm of morpholine, 0.3 ppm, <5 ppb of O 2 , room temperature pH~8.5, conductivity~2 µS/cm). One of the most important examples of CRUD-related issue is the clogging tube support plates.…”

“…The oxide that forms on stainless steels and nickel based alloys in PWR primary water usually comprises two layers. 13 The inner layer, only a few nanometres thick, consists of a protective Cr-rich layer (identified as NiCr 2 O 4 ) and grows by a solid-state diffusion mechanism. 20 It has been suggested that the inner layer comprises a Cr-oxide sublayer at the metal/oxide interface, which is the main contributor to protection from corrosion.…”