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Several in-core components in nuclear power systems are exposed to high-temperature water in the presence of radiation fields. The dynamic effect of radiation and water chemistry on material performance in these environments is not well understood partly due to significant experimental challenges. A facility consisting of a high temperature/pressure corrosion loop coupled with in-situ Raman spectroscopy has been commissioned to examine material behaviour in more realistic reactor conditions. The in-situ Raman component of the facility has been validated by conducting experiments with both pre-oxidized, and freshly abraded SS304L in water at 80 °C and 300 °C. Testing in water also revealed the detection limitations of the system. The assessment reported in this paper highlights the capabilities to perform degradation studies of key nuclear components by conducting in-situ characterization of materials exposed to high temperature water via Raman spectroscopy, thereby providing chemical, structural and semi-quantitative kinetic information. [ABSTRACT FROM AUTHOR]

The oxidation of Ni-Cr-Al model alloys was investigated after exposure to a 480 °C hydrogenated steam environment. Low angle grain boundaries (LAGBs) and the studied coincidence site lattice grain boundaries (CSLBs) showed intergranular oxidation, while high angle grain boundaries (HAGBs) were protected by an external oxide. The intergranular oxide consisted of a central Al-rich oxide, surrounded by a Cr-rich oxide. Al contribution in intergranular and external oxidation was enhanced in Ni-Cr-Al alloys compared to Ni-Al alloys. Thus, the third element effect is applicable at low homologous temperature along short-circuit diffusion pathways, in this case grain boundaries. • LAGBs and CSLBs were more susceptible to intergranular oxidation than random HAGBs. • The intergranular oxide had a central Al-rich oxide surrounded by a Cr-rich oxide. • The intergranular oxide in Ni-Cr-Al was more similar to Ni-Al than Ni-Cr alloys. • The third element effect operates along short-circuit grain boundaries at 480 °C. [ABSTRACT FROM AUTHOR]

The intergranular oxidation of binary Ni-xAl (x = 4, 7 at.%) and Ni-yCr (y = 11, 15 at.%) model alloys was studied in a 480 °C hydrogenated steam environment. It was observed that the intergranular oxidation susceptibility in Ni-Al and Ni-Cr alloys is different. In Ni-Al alloys, HAGBs are very susceptible to intergranular oxidation, while low energy grain boundaries behave similar to bulk material. In Ni-Cr alloys, LAGBs and CSLBs are susceptible to intergranular oxidation, while HAGBs are protected by an external oxide. The structure of the intergranular oxide was also different between Ni-Cr and Ni-Al alloys; the intergranular oxide formed in Ni-Al alloys was sharper and penetrated to greater depth compared with Ni- Cr alloys. Comparisons are made to previous testing of alloy 600 (Ni-16Cr-Fe) in similar environments, highlighting the potential effect of residual Al and Ti on the intergranular oxidation of the alloy. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, commercially available coatings of CrN, TiAlN and AlCrN were applied by physical vapour deposition to obtain 2–4 μm thick coatings on Zircaloy-4. The corrosion resistance, as well as the impact on hydrogen permeability of these coatings, was investigated. The latter is important with respect to hydrogen embrittlement of reactor components exposed to water with a certain dissolved hydrogen content. The corrosion resistance was investigated under pure water at 350 °C for 24 h and under CANDU conditions (300 °C and pH 10.5) for 30 days. Limited experiments were also performed in superheated steam (atmospheric pressure) at temperatures up to 1100 °C. Surface imaging (scanning electron microscopy) was performed before and after the exposure of the samples, with additional transmission electron microscopy analysis on a limited selection of samples. The composition of the coatings was determined by energy dispersive x-ray spectroscopy and depth characteristics were determined by secondary ion mass spectrometry. The CrN-coated samples have shown the best corrosion resistance to date, under pressurized water reactor, CANDU, and superheated steam conditions. Additionally, oxidation of the CrN and TiAlN coatings caused a significant reduction in the hydrogen uptake. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the presence of dissolved ferrous ion (Fe2+(aq)) on surface oxide film growth and conversion on carbon steel in pH 8.4 borate solutions was studied as a function of potential. The results of electrochemical measurements and surface analyses provide a consistent picture of oxide growth and conversion behaviour and the role of Fe2+(aq) on the oxidation. At potentials<−0.4VSCE the presence of Fe2+(aq) in solution somewhat suppresses the dissolution of FeII, thus reducing the net rate of anodic oxidation, while at potentials>−0.4VSCE the presence of Fe2+(aq) at 0.1mM can substantially increase the rate of formation of γ-FeOOH on the carbon steel surface via oxidation of Fe2+(aq). [Copyright &y& Elsevier]

Abstract: Surface oxide film growth and conversion on carbon steel at pH25°C 10.6 was studied as a function of temperature in a range of 25–80°C. The current behaviour observed as a function of various cyclic voltammetry scan conditions and the current and EIS spectra as a function of time during 7-d potentiostatic experiments all present consistent pictures of an oxide growth and conversion mechanism that depends mainly on electrode potential. At pH25°C 10.6 where the solubilities of both FeII and FeIII species are low, the chemical and phase composition of the oxide film formed on carbon steel depends on the electrode potential, but is independent of temperature. For the type of film formed, three potential regions can be defined: formation of a uniform and compact magnetite-like layer at potentials <−0.6VSCE, a uniform and compact maghemite-like layer in the range from −0.6 to 0.0VSCE, and small crystallites of γ-FeOOH on a compact layer at potentials >0.0VSCE. Although temperature influences the rates of thermal processes such as dissolution and charge transport through the oxide phase, and the Schikorr reaction at temperatures >70°C, these thermal processes do not influence the oxide composition, but instead influence only the thickness of the oxide film at pH25°C 10.6. [Copyright &y& Elsevier]

Abstract: The effect of γ-radiation on the kinetics of carbon steel corrosion has been investigated by characterizing the oxide films formed on steel coupons at 150°C and at two pH values. Results show that continuous irradiation enhances surface oxide formation with the type of oxide formed dependant on the solution pH. For experiments at 150°C and a [OH−] equivalent to that for pH25°C =10.6, the surface oxide on carbon steel after γ-irradiation was non-porous and uniform, and no localized corrosion was observed. This oxide, however, appears to be susceptible to brittle fracture during cooling. Raman spectroscopy of the surface film indicates that it is a mixture of the phases of Fe3O4 and γ-Fe2O3. In contrast, at 150°C with [OH−] equivalent to neutral pH25°C, metal dissolution is significant and the surface oxide film is very porous. Raman spectra show that this oxide film is also composed of a mixture of Fe3O4 and γ-Fe2O3. The results from this work combined with previously reported electrochemical studies of the same system as a function of pH and temperature can be used to deconvolute the effects of radiation, pH and temperature on the nature of the corrosion process. [ABSTRACT FROM AUTHOR]

The effect of ionizing radiation on steel corrosion is an important materials issue in nuclear reactors. In the presence of ionizing radiation water decomposes into both oxidizing and reducing species (e.g., OH, H2O2, O2−) whose net interactions with steels are not fully understood. The effect of radiation on the corrosion kinetics of carbon steel has been studied at pH 10.6 and room temperature, using electrochemical and chemical speciation analyses. The present study investigates the effect of γ-radiation on carbon steel corrosion and compares it with that of chemically added H2O2, which is considered to be the key radiolytically produced oxidant at room temperature. Various oxide films were pre-grown potentiostatically on carbon steel electrodes, and then exposed to either γ-radiation at a dose rate of ∼6.8 kGy h−1 or to H2O2 in a concentration range of 10−6 to 10−2 M. The corrosion kinetics were studied by monitoring the corrosion potential (ECORR), and periodically performing linear polarization (LP) and electrochemical impedance spectroscopy (EIS) measurements. [Copyright &y& Elsevier]

Abstract: Surface oxide film growth and conversion processes on carbon steel were studied using a range of electrochemical techniques and ex situ surface analyses. The electrochemical study included (i) cyclic voltammetry as a function of various scan conditions and (ii) 7-day potentiostatic oxidation at a range of potentials while periodically performing Electrochemical Impedance Spectroscopy. Carbon steel surfaces at various stages of electrochemical oxidation were examined by SEM, Raman and X-ray photoelectron spectroscopy (XPS). These studies yield a consistent picture of film formation/conversion processes on carbon steel at pH 10.6, which is different to that reported for basic solutions (pH>13). Oxide film formation/conversion mechanisms for three potential regions are proposed. In region I (≤−0.6V vs SCE), the main oxide formed is Fe3O4 which grows via a solid-state process; in region II (−0.5V≤ E (vs SCE)≤−0.2V), continuous growth of the Fe3O4 layer is accompanied by its anodic conversion to a more maghemite (γ-Fe2O3)-like phase near, or at, the oxide/solution interface by a similar solid-state mechanism to that described for region I; in region III (0.0V< E (vs SCE)<0.4V), the anodic conversion of this Fe3O4/γ-Fe2O3 oxide to γ-FeOOH leads to a significant structural change, which can lead to film fracture and the introduction of enhanced transport pathways in the film. [Copyright &y& Elsevier]

• Ag-In alloys are susceptible to internal oxidation at relatively low temperatures. • Increasing indium concentration leads to increase in nodule size and area density. • Area density of nodules on the surface can be a function of grain orientation. • Grain boundary misorientation angle affects its internal/intergranular oxidation. • A porous oxide structure, and two different nodule structures were observed. Internal oxidation of Ag-xIn alloys (x = 10, 13, 16 at%) was studied in an air atmosphere at a relatively low homologous temperature (240 °C), where lattice diffusion is negligible. After exposure, metallic Ag nodules were present on the surfaces of all alloys, expelled to relieve stress due to internal oxidation, confirming that such coarse morphologies can be produced by short-circuit transport. Crystallographic orientation and grain boundary misorientation were found to influence nodule expulsion tendency, and the propensity for internal or external oxidation. Further analytical TEM characterization was used to study the nanoscale morphology and chemistry of nodules and internal oxide(s). [ABSTRACT FROM AUTHOR]

A novel Thomson-scattering diagnostic with continuous angular resolution over a span of 120° was developed for the characterization of plasmas produced at the Omega Laser Facility. Spectrally resolving light scattered from electron plasma wave features as a function of emission angle provides a means to efficiently probe a large range of plasma frequencies and k vectors. Together, these spectra contain critical constraints on the plasma-physics models used to interpret the data and enable experimental measurements of the electron-velocity distribution function over several orders of magnitude without assumptions about its mathematical form. Major components of the instrument include (1) a reflective collection objective that gathers light over a range of 120° × 12°; (2) a spatial-filter image relay for measurement localization; (3) cylindrical optics for producing a line image of the collection aperture; (4) a transmission grating spectrometer; and (5) a time-gated, image-intensified camera. Thomson-scattered light collected from an ∼ 50 − μ m 3 volume of plasma is recorded with 0.8-nm spectral and 1° angular resolution. Initial experiments examined the properties of the electron-velocity distribution in gas-jet-produced plasmas in the presence of heating via inverse bremsstrahlung absorption. [ABSTRACT FROM AUTHOR]

Selective dissolution (dealloying) of more reactive elements from a solid solution alloy can result in the formation of a nanoporous surface layer enriched in the more noble elements. For example, in Alloy 800 (wt.% Fe-32Ni-21Cr), a remnant nanoporous Ni-rich film is formed following the selective dissolution of Fe and Cr in boiling 50 wt.% NaOH caustic solutions (135–140 °C). This surface film has been proposed to act as a precursor to stress corrosion cracking (SCC) by a cleavage mechanism. This study investigates the effect of crystallographic orientation on the characteristics of a dealloyed layer (i.e., thickness and size of ligaments/pores) formed on Alloy 800. Electron backscattered diffraction (EBSD) is used to correlate grain orientation with the geometry and morphology of the dealloyed layer formed in the boiling caustic environment. Results indicate that the dealloyed layer formed on grains with planes close to the { 111 } family on the sample surface, has a finer geometry (i.e., a thinner layer compared with other grain orientations and consisting of smaller diameter ligaments). Further SCC experiments on Alloy 800 specimens revealed a lower density of cracks initiated from surface planes that were close to { 111 } , confirming a link between dealloyed layer geometry, texture, and SCC. [Display omitted] [ABSTRACT FROM AUTHOR]

Alloy X-750 was exposed to a 480 °C CO-CO 2 reducing gas mixture at an oxygen partial pressure below the NiO dissociation pressure. Post-exposure analytical transmission electron microscopy (ATEM) analysis confirmed the occurrence of preferential intergranular oxidation (PIO) and internal oxidation which resulted in the formation of Ni nodules. Thus, reducing CO-CO 2 mixtures can promote PIO in Alloy X-750, similar to Alloy 600 exposed to similar oxygen partial pressure but in H 2 -steam environment. In Alloy X-750, intergranular oxidation of Ti and Al were observed to occur prior to Cr oxidation, while the presence of intergranular Cr carbides hinders PIO penetration depth. • CO-CO2 mixtures can promote internal and intergranular oxidation in X-750. • Results are similar to observed in Alloy 600 exposed to H2-steam. • Intergranular oxidation front is led by Ti and Al. [ABSTRACT FROM AUTHOR]

Oxidation experiments on Alloy X-750 were performed in reducing CO-CO 2 mixtures to assess the possibility of preferential intergranular oxidation (PIO) in relation to CANDU garter-spring spacers. The testing environments simulate hypothetical off-chemistry scenarios, promoting the oxidation of the alloying elements, but not Ni. Surface and cross-section microscopy corroborated by Auger electron spectroscopy confirmed the occurrence of internal and intergranular oxidation in Alloy X-750, accompanied by Ni nodule expulsion to the surface. Results are qualitatively similar to observations in Alloy 600 exposed to 480°C hydrogenated steam, used as an accelerated environment for primary water stress corrosion cracking (PWSCC) testing. [ABSTRACT FROM AUTHOR]

The National Ignition Facility (NIF) is a 192 laser beam facility designed to support the Stockpile Stewardship, High Energy Density and Inertial Confinement Fusion (ICF) programs. We report on the design of an Optical Thomson Scattering (OTS) diagnostic that has the potential to transform the community's understanding of NIF hohlraum physics by providing first principle, local, time-resolved measurements of under-dense plasma conditions. The system design allows operation with different probe laser wavelengths by manual selection of the appropriate beam splitter and gratings before the shot. A deep-UV probe beam (λ0-210 nm) will be used to optimize the scattered signal for plasma densities of 5 × 1020 electrons/cm3 while a 3ω probe will be used for experiments investigating lower density plasmas of 1 × 1019 electrons/cm3.We report the phase I design of a two phase design strategy. Phase I includes the OTS telescope, spectrometer, and streak camera; these will be used to assess the background levels at NIF. Phase II will include the design and installation of a probe laser. [ABSTRACT FROM AUTHOR]

Objective: To evaluate residual platelet activity in a consecutive cohort of patients treated with dual antiplatelet therapy after coronary stent implantation Design: Prospective single-centre cohort study. Setting: University hospital in Germany. Patients: 480 patients with symptomatic coronary artery disease (n = 221 (46%) or acute coronary syndrome (ACS; n = 259 (54%) stable angina) were studied. Platelet activity was measured by collagen- (5 ~igIml) and adenosine diphosphate- (ADP; 20 jimol/l) induced platelet aggregation to assess post-treatment activity in patients treated with acetylsalicylic acid (500 mg bolus intra- venously followed by 100 mg once a day) and clopidogrel (600 nig loading dose followed by 75 mg once a day) Main outcome measures: Increased residual platelet activity (IRPA) was defined if platelet aggregation was in the upper tertile of values in the patient collective. Association of epidemiological factors with IRPA was evaluated in a multivariate logistic regression analysis. Results: IRPA-ADP was found in 53 patients (11.0%) and IRPA-collagen in 42 patients (8.8%). ACS was associated with IHPA independently from other factors (for IRPA- collagen: odds ratio (OR) = 2.3, 95% confidence interval (Cl) 1.2 to 4.5, p<0.05; for IRPA-ADP: OR = 2.4; 95% Cl 1.3 to 4.4, p<0.Ol; for IRPA-ADP/collagen: OR = 4.5, 95% Cl 1.2 to 16.9, p