Mechanism of hydrogen absorption during the exposure of alloy 600-like single-crystals to PWR primary simulated media

Jambon, Fanny; Marchetti, L.; Jomard, François; Chêne, J.

doi:10.1016/j.jnucmat.2011.04.066

Cited by 32 publications

(10 citation statements)

References 14 publications

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“…At first sight, it seems that H should not have noticeable effects in these conditions. Nevertheless, it is hard to determine experimentally the local H concentration, even using secondary ion mass spectrometry on samples oxidized in well-controlled conditions [15,16], let alone in the nanometer-scale process zone of a stress corrosion crack [13]. Local H concentrations beyond 1000 ppm cannot be excluded, making it necessary to consider the implication of SAVs in PWR conditions.…”

Section: Resultsmentioning

confidence: 99%

“…However, the role of local strain is not explained and other mechanisms could play direct or indirect roles. For example, absorbed H, produced during depassivation/repassivation events [15,16], could directly embrittle the GBs or participate indirectly by enhancing Cr transport via SAV formation. It was shown by Ni/Cu interdiffusion experiments [17] that SAVs can indeed increase diffusion by many orders of magnitude.…”

Section: Introductionmentioning

confidence: 99%

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Stability of vacancy-hydrogen clusters in nickel from first-principles calculations

2014

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The interactions of hydrogen (H) atoms with vacancies are investigated by means of ab initio calculations. The lowest segregation energies are À0.27 and À0.41 eV at single vacancies and divacancies, respectively. These values are in excellent agreement with those corresponding to the two characteristic peaks of the thermal desorption spectra. The microscopic interpretation of the experimental data is therefore clarified. An energetic model is built from the ab initio data and used to study the influence of H bulk concentration and temperature on the concentration of vacancy-H clusters. Analytical expressions, validated by Monte Carlo simulations, are given. The mean vacancy occupation and the H-induced vacancy enrichment are calculated at two temperatures representative of H embrittlement experiments and stress corrosion cracking at high temperatures. The stability domain of VH 6 clusters is found to significantly overlap with the experimental conditions for embrittlement. Therefore, vacancy clustering at high concentrations can be qualitatively discussed based on VH 6-VH 6 interactions that are found weakly repulsive. Consequences on H damage in Ni are discussed. The effect of metal vibrations on segregation and local hydride stability is qualitatively evaluated by off-lattice Monte Carlo simulations using a semi-empirical Ni-H potential. They are shown to shift local hydride stability towards higher H concentrations.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Stability of vacancy-hydrogen clusters in nickel from first-principles calculations

2014

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“…Surface state following various grinding and polishing processes is a key factor influencing the corrosion behaviour [10,11]. To date, a number of studies have been carried out to clarify the effect of surface state on corrosion of austenitic stainless steels and nickelbase alloys in high temperature water, which showed that the ground, mechanical polished and electropolished surfaces had different corrosion behaviours [13][14][15][16][17][18][19][20][21][22][23][24][25]. The effect of electropolishing on corrosion is one focus of these studies.…”

Section: Introductionmentioning

confidence: 99%

Effect of electropolishing on corrosion of Alloy 600 in high temperature water

et al. 2015

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“…A comparison with diffusion data at high temperature suggests an acceleration of transport by several orders of magnitude [20], likely caused by a large amount of out of equilibrium vacancies injected in the material [21] during oxidation. On the other hand, much effort has been devoted to determine the growth mechanism of the oxide and prove the hydrogen uptake [22][23][24]. Understanding the interplay between H and vacancies during diffusion is important for the modeling of * dome.tanguy@univ-lyon1.fr H degradation, for room temperature embrittlement, and for intermediate temperature oxidation.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen influence on diffusion in nickel from first-principles calculations

2015

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We propose a method to evaluate the diffusion coefficient of vacancy-hydrogen clusters (VH n ) in metals. The key is a good separation of time scales between H diffusion and the metal-vacancy exchange. The Ni-H system is investigated in details, using ab initio calculations, but the arguments can be transposed to other systems. It is shown that cluster diffusion can be treated as an uncorrelated random walk and that H is always in equilibrium before the vacancy-metal exchange. Then, the diffusion coefficient is a sum over jump paths of the equilibrium probability of being in a specific VH n configuration times the corresponding activation terms. The influence of H on the energy barrier is well reproduced by effective pair interactions between the jumping Ni and the H atoms inside the vacancy. This model is motivated by an analysis of the electronic charge redistribution in key saddle configurations. The interaction is repulsive and decreases with distance. The model is used to find easy jump path, reduce the number of saddle searches, and provide an estimate of the error expected from this reduction. The application to the Ni-H system shows that vacancies are drastically slowed down by H. The effects of temperature and bulk H concentration are explored and the origin of the non-Arrhenius behavior is explained. At equilibrium, VH n clusters always induce a speedup of metal diffusion. The implications concerning H induced damage, in particular in regards to Ni-Cr oxidation, are discussed.

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Mechanism of hydrogen absorption during the exposure of alloy 600-like single-crystals to PWR primary simulated media

Cited by 32 publications

References 14 publications

Stability of vacancy-hydrogen clusters in nickel from first-principles calculations

Stability of vacancy-hydrogen clusters in nickel from first-principles calculations

Effect of electropolishing on corrosion of Alloy 600 in high temperature water

Hydrogen influence on diffusion in nickel from first-principles calculations

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