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Secondary Ion Mass Spectrometry is an important technique for the study of the composition of a wide range of materials because of the exceptionally high sensitivity that allows the study of trace elements and the ability to distinguish isotopes that can be used as markers for reactions and transport processes. However, when studying nuclear materials, it is often necessary to analyse highly radioactive samples, and only rather few SIMS facilities are available in active environments. In this paper, we present a methodology using focussed ion beam milling to prepare samples from radioactive specimens that are sufficiently large to undertake SIMS mapping experiments over microstructurally significant regions, but with overall activities small enough to be readily transported and analysed by a SIMS instrument in a normal laboratory environment. Radioactive samples prepared using this methodology can also be used for correlative SIMS analysis with other analytical microscopies. SIMS results showing the distributions of deuterium in oxides on in‐reactor corroded zirconium alloys are presented to demonstrate the potential of this sample preparation technique. [ABSTRACT FROM AUTHOR]

Zirconium alloys, are usually used as fuel cladding materials in VVER (water-cooled, water-moderated energy reactor) type reactors, mainly, due to their low neutron absorption cross-section, desirable mechanical properties, and good corrosion resistance under reactor operating conditions. During exposure to water at high temperature, water reacts with zirconium alloys, which results in the production of an oxide layer. The entire area of corrosion along with the accompanying absorption of hydrogen in the zirconium metal matrix has attracted a lot of attention when the performance of the core components as well as the operation of the reactor is emphasized. The growth of the zirconium oxide layer plays a destructive role in decreasing thermal efficiency of the reactor by restricting the inlet temperature and chemical properties of the coolant. The present study aimed to develop a computer code to predict long-term water side corrosion weight gain, oxide thickness and determine the concentration of absorbed hydrogen in VVER-1000 reactors during normal operating conditions. The proposed model can be utilized to estimate the pre-transition and post-transition corrosion weight gain and the oxide thickness in operating conditions.

Oxidation of metals by water generates hydrogen which can enter the solid causing serious degradation of its mechanical properties and may also influence the corrosion rate. The present work focuses on hydrogen pickup during the corrosion of zirconium alloys in an aqueous environment. Transmission electron microscopy using Fresnel imaging on three different samples of oxidized Zr has been used to study the type, distribution, concentration and connectivity of nano-porosity as a function of depth through the oxide layer. Extensive interconnected nano-pipes are found in the non-protective outer part of the oxide, while in the protective barrier layer closer to the metal-oxide interface, continuous nano-pipes turn into individual nano-pores. Ab initio calculations show that molecular hydrogen is formed spontaneously by the reaction of water with oxygen vacancies in zirconium oxide. Molecular dynamics simulations reveal that these H 2 molecules can diffuse rapidly through nano-pores and nano-pipes as small as 0.5 nm in the oxide layer. Calculations demonstrate that molecular hydrogen dissociates spontaneously on surfaces of suboxides found experimentally at the metal-oxide interface. Oxygen vacancies in ZrO enable the ingress and diffusion of H atoms with an energy barrier of approximately 65 kJ/mol. Further diffusion of hydrogen through oxygen-saturated α -Zr metal is fast, leading to the formation of thermodynamically stable zirconium hydrides. Thus, formation and diffusion of molecular hydrogen through nano-pores in the bulk oxide and ingress of H atoms via suboxides is a possible mechanism of hydrogen pickup in any metal or alloy covered by an oxide scale that contains nano-porosity. Image 1 [ABSTRACT FROM AUTHOR]

The paper deals with the effect of the electrolyte composition on the protective properties of the PEO-coating on the Zr–1Nb zirconium alloy. To assess the functional properties of the coatings and their topography and microstructure, elemental and phase contents are studied and electrochemical and accelerated operational tests are performed to identify the most efficient electrolyte. It is found that the coatings obtained in the silicate-phosphate electrolyte exhibit the best protective properties. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Nuclear Technology & Radiation Protection is the property of Vinca Institute of Nuclear Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we focus mainly on evaluating the anisotropy evolution in Zircaloy-4 tubes with respect to hydrogen pickup which tends to affect the deformation behavior and fracture elongation due to embrittlement phenomenon induced by Zr hydrides. To capture the complex material behaviors of the H-charged (166 ppm) Zircaloy-4 tubes, we have applied the Hill anisotropic yield criterion by carrying out several material tests, such as the axial tensile, ring tensile, and axial crushing tests, for calibrating the anisotropic coefficients based on the directional strength and strain ratios. It makes possible to simulate the directional flow curves of the as-received and the H-charged Zircaloy-4 tubes based on the directional strength ratios along the axial and hoop directions, respectively, as well as a variation in deformation modes in the axial crushing test with substantial accuracy. [ABSTRACT FROM AUTHOR]

Hydrogen pickup during nuclear fuel cladding corrosion is a critical life-limiting degradation mechanism for nuclear fuel. Following a program dedicated to zirconium alloys, corrosion, it has been hypothesized that oxide electronic resistivity determines hydrogen pickup. In-situ electrochemical impedance spectroscopy experiments were performed on Zircaloy-4 and Zr-2.5Nb alloys in 360 °C water. The oxide resistivity was measured as function of time. The results show that as the oxide resistivity increases so does the hydrogen pickup fraction. The resistivity of the oxide layer formed on Zircaloy-4 is higher than on Zr-2.5Nb, resulting in a higher hydrogen pickup fraction of Zircaloy-4, compared to Zr-2.5Nb. [ABSTRACT FROM AUTHOR]

Oxidation reaction is inevitably consuming the thickness of load bearing matrix of Zircaloy-4 and releases hydrogen that can be ingress into the matrix, thereby resulting in the degradation of its structural integrity. The present work aims to simultaneously investigate the oxidation behavior, hydrogen pickup, and the associated microstructure evolution of Zircaloy-4 exposed to 800 °C–1000 °C pure steam. Gain weight, growth of the oxide layer and α-Zr(O) layer in Zircaloy-4 follow the parabolic law. The intensification of oxide corrosion versus temperature and duration time is attributed to the severe Sn segregation that leads to the oxide layer delamination. α-Zr(O) layer just appeared when the oxidation temperature does not exceed the phase transition temperature. Radial cracks are prone to initiating at the concave position of the oxide/metal undulation interface. The hydrogen pickup measured by vacuum hot extraction was no more than 40 ppm, and no precipitated hydrides were identified. A mild Sn segregation in the outer oxide layer has a small influence in deteriorating the outer oxide layer protectiveness, the hinder effect of an unbroken outer oxide layer to the diffusion of hydrogen into the α-Zr(O) layer and matrix metal, and then resulting in a smaller influence of hydrogen embrittlement in this study. • Phase transition temperature is the determinant factor for the formation of α-Zr(O) layer. • The hinder effect of unbroken outer oxide layer to the hydrogen ingression leads the lower hydrogen pickup. • The concave position of O-M interface is the preferred site for initiating the crack in α-Zr(O). • Heterogeneous strain distribution in the prior-β region might deteriorate the remained ductility of oxidized Zircaloy-4. • The correlation among oxide behavior, hydrogen pickup and Sn inhomogeneity segregation in the oxide layer is clarified. [ABSTRACT FROM AUTHOR]

Zircaloy-4 samples with various levels of Ni content (0–483 wt. ppm) were exposed in autoclave for up to 2800 days. Samples were destructively and non-destructively measured to determine the weight gain from oxidation and hydrogen contents to better understand the role hydrogen has in increasing oxide growth rates and to study the effect of Ni on the mechanism of hydrogen pickup in Zr alloys. Overall, additions of Ni lead to significantly higher hydrogen pickup of the alloy. As observed previously, at higher weight gains, a small decrease in hydrogen pickup fraction is observed for all alloys tested (Zircaloy-4 with and without Ni). A small beneficial effect of Ni was observed on corrosion rate when controlling for the amount of hydrogen in the material, which potentially indicates that if hydrogen content were controlled via other means (e.g., volume or other alloy additions) Ni may improve corrosion resistance of the material. Results generally support published density functional theory (DFT) hypotheses that point to an increase in hydrogen solubility or catalysis of surface reactions as the mechanism by which Ni increases hydrogen pickup. Data or future corrosion testing of alloys with Ta, V, or Ti additions could further support or refute these theories by testing aspects of the proposed mechanisms. [ABSTRACT FROM AUTHOR]

Zircaloy is extensively used as a nuclear fuel cladding tube material. The fuel cladding encapsulates radioactive fuel pellet and it is resorted to an exceptionally harsh environment which is the combination of high temperature, high stresses, a chemically aggressive coolant and intense radiation fluxes. Hydrogen or deuterium produced as a result of aqueous corrosion of Zircaloy cladding diffuses into its matrix. Hydrogen diffused into Zircaloy fuel cladding beyond the terminal solid solubility precipitates out as brittle hydride phases. The precipitation of brittle hydride degrades the mechanical properties of Zircaloy so severely that it limits the service life of fuel cladding and may even cause its failure. The failure of Zircaloy cladding due to hydrogen ingress into its matrix is called hydrogen embrittlement or hydride-induced embrittlement. The phenomenon of hydrogen embrittlement is deeply dependent on the behaviour of hydrogen inside the lattice of Zircaloy subjected to the harsh and highly transient conditions of nuclear reactor as a fuel cladding. A plethora of investigations on hydrogen embrittlement has already been reported in the literature. The research investigations pertaining to hydrogen embrittlement are highly scattered with contradictory outcomes. The present article attempts to succinctly summarize relevant research works in order to develop simplistic and coherent understanding of this complex phenomenon, apart from highlighting the thrust areas which require further investigations. [ABSTRACT FROM AUTHOR]

Under normal operation condition of nuclear power plants, there may exist some special phenomena related to high burnup fuel cladding, such as breakaway oxidation, inner surface oxygen ingress and hydrogen pickup embrittlement. The effects of these phenomena on cladding fracture limit during LOCA conditions were investigated by fuel cladding research program sponsored by U.S. NRC. Based on the research, new LOCA acceptance criterion 10CFR50.46c draft was agreed and released. In the present study, research on compliance between large break LOCA of HPR1000 and new LOCA acceptance criterion 10CFR50.46c was performed. Firstly, a hydrogen content prediction model for different cladding material was innovatively proposed and then large break LOCA analysis of HPR1000 at different burnup points was performed. Research showed that the analysis results of large break LOCA of HPR1000 could meet requirement of 10CFR50.46c. The PCT and transient ECR margin were 190.1 °C and 10.1% respectively which were large enough for large break LOCA to ensure reactor core safety. • A hydrogen content prediction model for different cladding material was innovatively proposed. • LBLOCA analysis of HRP1000 was performed at different burnup points by adopting self-developed codes LOCUST and CATLAPA. • Research on compliance between LBLOCA of HPR1000 and 10CFR50.46c was performed for the first time. [ABSTRACT FROM AUTHOR]

An incidence of delayed catastrophic cracking in commercially processed low nickel austenitic stainless steel coils during unwinding of the material at a customer's end has been investigated. The fracture surfaces of failed steel coil samples revealed a brittle intercrystalline mode of fracture with typical manifestations of clear grain facets. Optical and scanning electron microscopy of polished, unetched steel specimens exposed a preponderance of branched as well as discrete stepwise microcracks, commonly observed in hydrogen-induced delayed failures. The specimens, electrolytically etched in 10% oxalic acid, were found to exhibit pronounced intergranular cracking, stepwise microcracking, grain dropping, and intergranular ditching in the annealed austenite microstructure of low nickel stainless steel. Investigations also revealed unusual levels of residual hydrogen to the extent of 11 ppm in steel specimens and a marked loss of tensile ductility was also noticeable in the defective steel with elongations barely approaching 8% in comparison to an overall elongation of 50% at the time of its dispatch to the customer. Based on the delayed nature of cracking, which transpired at customer's premises after several days/months of dispatch, and the fact that the failure of the coils occurred at the time of uncoiling, when the operating stresses are well below the yield point of the material, it is surmised that the failure is attributable to hydrogen-induced damage. This article also takes a critical look at the possible sources of hydrogen pickup during steel making and elucidates remedial measures for control of hydrogen content in steels. [ABSTRACT FROM AUTHOR]

Abstract: To understand the basic oxidation kinetics of alloying elements which is considered to be strongly related with the corrosion and hydrogen pickup, the depth profiles of chemical states of alloying elements (Cr and Fe) were measured in the oxide layer of Zr-0.5Sn-1.0Cr-0.5Fe alloys. The depth profiles were obtained by combinations of a surface-sensitive XANES and an extremely low energy Ar ion sputtering. The XANES measurements revealed that the chemical states of alloying elements (Fe and Cr) varied with the depth in the oxide layer. Especially in the oxide layer formed in steam, a decrease of the fractions of oxidation states was significant rather than that in LiOH solution. In the oxide layer formed in steam, the oxidation rate of chromium was faster than iron by a factor of approximately 2. [Copyright &y& Elsevier]

• Mass gain of pure Zr at 900–1100 °C steam was reduced to 22–45% by ZrO 2 /Cr composite coating. • PEO interlayer suppressed hydrogen permeation into Zr substrate during steam oxidation. • Steam oxidation mechanisms of bare and ZrO 2 /Cr-coated pure Zr were discussed. Plasma electrolytic oxidation (PEO) and filtered cathodic vacuum arc deposition (FCVAD) techniques were employed to fabricate a ZrO 2 /Cr composite coating on pure zirconium. The steam oxidation properties of bare and ZrO 2 /Cr-coated pure Zr were performed in water vapor environment at 900–1100 °C. Their morphologies, microstructures and phase constituents before and after steam oxidation were analyzed. Meanwhile, their composition depth profiles were measured by glow discharge optical emission spectroscopy (GDOES). It was found that the mass gain of ZrO 2 /Cr-coated Zr was about 22–45% of that of bare Zr after 3600 s steam oxidation at 900–1100 °C, and the PEO and FCVAD composite treatments significantly improved the steam oxidation resistance of Zr. After steam oxidation, the phosphorous element in the outer layer of PEO film from phosphate electrolyte diffused into the residual Cr layer, however, most of the phosphorous in the interior of PEO layer was remained although the phosphorus diffusion in the region was accelerated with the increase of steam temperature. The ZrO 2 to Zr 3 O phase transformation in PEO intermediate layer occurred in high temperature steam. Furthermore, the PEO zirconia interlayer suppressed hydrogen permeation into the Zr substrate during steam oxidation at 900–1100 °C. [ABSTRACT FROM AUTHOR]

• Long-term monitoring of in-situ electrochemical polarization curves were conducted. • Cathodic reaction is activation-controlled, while anodic reaction is diffusion-controlled. • Different hydrogen evolution reaction mechanisms with corrosion time are observed. • Recombination of H atoms becomes harder with time in pre-transition stage. • HER mechanisms can be used to interpret the behaviors of hydrogen pickup of Zr. Long-term on-line monitoring of in-situ electrochemical polarization curves were conducted on two zirconium claddings during corrosion in 360 °C water. Results suggest that cathodic reaction is activation-controlled, while anodic reaction is diffusion-controlled. Cathodic Tafel constants match well with the value predicted by Tafel kinetics and different hydrogen evolution reaction mechanisms of alloys with corrosion time are observed. Generally, recombination of hydrogen atoms becomes harder with time and is even harder in one of the alloys, which is proposed to increase the diffusion probability of hydrogen atoms into zirconium matrix. This proposal is in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

• Fresnel imaging in the TEM has been used to identify different types of porosity in the protective oxide near the "barrier layer", around 0˜200 nm from the metal-oxide interface. • More disorganised oxide grains and nano-porosity network is found by TEM and TKD in rapidly oxidising samples. • NanoSIMS analysis suggests that the transition event enables the propagation or trapping of deuterium while the pre-transition sample is a good barrier to deuterium penetration. • APT data provides strong direct evidence for D segregation in the "barrier layer" at oxide grain boundaries and nano porosity. • The nanopores, if interconnected, can be the dominant pathway for hydrogen transport to the metal matrix. We have used (S)TEM, TKD, NanoSIMS and APT to study nano-porosity in the oxide grown on deuterated Zr-1.0Nb and Zr-2.5Nb alloys. A detailed analysis of "barrier layer" nano-porosity by TEM and TKD has revealed that the oxide grain structure is much more disorganised and the nano-porosity network better developed in the rapidly oxidising post-transition alloy. Direct observations of the trapped deuterium (D) distributions from NanoSIMS analysis also shows much more penetration of the oxide layer post-transition. APT analysis shows that there is Fe and D segregation to some of the oxide grain boundaries with occasional evidence of porosity containing trapped D and H. We conclude that interconnected porosity would offer a dominant pathway for the transport of hydrogenic species to the metal substrate during the aqueous corrosion of zirconium alloys in service. [ABSTRACT FROM AUTHOR]