Continuum model for hydrogen pickup in zirconium alloys of LWR fuel cladding

Wang, Xing; Zheng, Mingjie; Szlufarska, Izabela; Morgan, Dane

doi:10.1063/1.4979472

Cited by 8 publications

(5 citation statements)

References 45 publications

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“…Consistent with our previous work [69] and other studies [61], we assume the existence of a charge gradient across the oxide layer that originates from the onset of an electron density profile [75]. As well, in this work we consider autoclave conditions and thus neglect the thermomigration contribution.…”

Section: Diffusion Model Of Hydrogen In Zromentioning

confidence: 66%

“…This, known as the pickup fraction, sets the boundary condition for the adsorption of hydrogen at the clad's surface. Adsorbed H 2 molecules can split into atomic hydrogen by a number of processes [65,66], although whether this atomic H appears in a neutral or charged state in the metal is still an issue under debate [61,65]. Hydrogen atoms diffuse through the oxide layer and reach the oxide/metal interface, from which they can enter the α-Zr substrate and undergo a number of processes depending on temperature and concentration.…”

Section: Zr-clad Hydrogen Chemistrymentioning

confidence: 99%

“…This is the accepted picture during the pre-transition regime, as, after that, fast H transport then occurs through percolated crack networks formed in the oxide layer [59]. However, there is contradicting evidence in the literature about this [60,61], and it is not clear what effect a dynamic boundary condition might have on hydrogen precipitation in the metal substrate at higher temperatures, and what the evolution of the hydride microstructure will be in those conditions. With the objective of shedding new light on these and other issues by using new computational and experimental understanding, in this paper, we present an comprehensive hydrogen transport and precipitation model in Zr formulated from first principles reaction kinetics and fundamental thermodynamics and mechanics.…”

Section: Introductionmentioning

confidence: 99%

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Kinetic Model of Incipient Hydride Formation in Zr Clad under Dynamic Oxide Growth Conditions

Reyes

Shah

et al. 2020

Materials

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The formation of elongated zirconium hydride platelets during corrosion of nuclear fuel clad is linked to its premature failure due to embrittlement and delayed hydride cracking. Despite their importance, however, most existing models of hydride nucleation and growth in Zr alloys are phenomenological and lack sufficient physical detail to become predictive under the variety of conditions found in nuclear reactors during operation. Moreover, most models ignore the dynamic nature of clad oxidation, which requires that hydrogen transport and precipitation be considered in a scenario where the oxide layer is continuously growing at the expense of the metal substrate. In this paper, we perform simulations of hydride formation in Zr clads with a moving oxide/metal boundary using a stochastic kinetic diffusion/reaction model parameterized with state-of-the-art defect and solute energetics. Our model uses the solutions of the hydrogen diffusion problem across an increasingly-coarse oxide layer to define boundary conditions for the kinetic simulations of hydrogen penetration, precipitation, and dissolution in the metal clad. Our method captures the spatial dependence of the problem by discretizing all spatial derivatives using a stochastic finite difference scheme. Our results include hydride number densities and size distributions along the radial coordinate of the clad for the first 1.6 h of evolution, providing a quantitative picture of hydride incipient nucleation and growth under clad service conditions.

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Section: Diffusion Model Of Hydrogen In Zromentioning

confidence: 66%

Section: Zr-clad Hydrogen Chemistrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Kinetic Model of Incipient Hydride Formation in Zr Clad under Dynamic Oxide Growth Conditions

Reyes

Shah

et al. 2020

Materials

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“…In addition, it is reasonable to expect that interstitial O will affect the diffusion of H in bulk Zr, generally. In most studies addressing the ability of H to diffuse into Zr, the focus is the effect of ZrO 2 on this process [9,10]. As we will show here, interstitial O will also act as hydrogen traps that can have a notable effect on the diffusion process.…”

Section: Introductionmentioning

confidence: 86%

Denuded zones in zirconium pressure vessels: oxygen’s role examined via multi-scale diffusion model

Liyanage

Miller

Rajapakse

2020

Modelling Simul. Mater. Sci. Eng.

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Zirconium alloys are extensively used as cladding material in nuclear reactors. They are vulnerable to hydrogen degradation under the harsh service conditions of the reactors. Optical micrographs taken in some pressure tubes shows the presence of hydride denuded zones closer to the surface, where the hydrides formed in this region are smaller in size compared to the bulk. We investigated the effect of oxygen on diffusivity of hydrogen in α Zr, to check the hypothesis that oxygen slows the diffusion of hydrogen and thereby encourages the occurrence of hydride denuded zones. We used a multi-scale model to simulate H diffusion in Zr with different O concentrations to identify the effect that O has on H diffusivity. From the study we found that oxygen indeed decreases the diffusivity of hydrogen in α Zr for moderate oxygen concentrations. We investigated the diffusion processes of individual H atoms, which showed that the reduction in diffusivity is caused by a decrease in the hopping rates and the formation of hydrogen traps by the combination of several interstitial sites. Though the diffusivity of H seems to be reduced by O, looking at the O concentration profiles found in Zircaloy pressure tubes, we see that the slowing down is insufficient to cause a significant enough change to the size of hydride precipitates. This causes us to reject the hypothesis as the main reason for the formation of denuded zones in Zircaloy pressure tubes.

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“…The hydrogen atom released in the process of oxidation of Zr (Reaction 1) either combines with another to form a hydrogen molecule (resulting in Equation ) or diffuses into the zirconium metal (Equation ). Some of the hydrogen produced during the surface oxidation permeates through the protective Zr oxide layers, diffuses, and accumulates in Zr metal . The remaining hydrogen, not absorbed by the cladding material, is carried away by the reactor coolant.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen evolution and corrosion behavior of zirconium tubing in sub‐ and supercritical water

Choudhry

Svishchev

2019

Materials & Corrosion

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Hydrogen evolution is inevitable during the oxidation of zirconium in high‐temperature water. A fraction of this evolved hydrogen diffuses into the cladding material, and the remaining is carried away by the reactor coolant. In this study, hydrogen evolution and corrosion behavior of zirconium‐702 in high‐temperature water are investigated using a continuous tubular flow‐through reactor. The results show that at a constant pressure of 25 MPa, the evolution of hydrogen gas from an oxidized zirconium reactor surface is approximately 24 times larger at 500°C than at 350°C. At higher temperatures, the zirconium reactor tubing exposed to water shows ballooning, with bending before the rupture near the exit end of the reactor tube, where the concentration of evolved hydrogen is the highest.

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Continuum model for hydrogen pickup in zirconium alloys of LWR fuel cladding

Cited by 8 publications

References 45 publications

Kinetic Model of Incipient Hydride Formation in Zr Clad under Dynamic Oxide Growth Conditions

Kinetic Model of Incipient Hydride Formation in Zr Clad under Dynamic Oxide Growth Conditions

Denuded zones in zirconium pressure vessels: oxygen’s role examined via multi-scale diffusion model

Hydrogen evolution and corrosion behavior of zirconium tubing in sub‐ and supercritical water

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