Fission gas release from UO2 nuclear fuel: A review

Rest, J.; Cooper, M.W.D.; Spino, J.; Turnbull, J.A.; Uffelen, P. Van; Walker, C.T.

doi:10.1016/j.jnucmat.2018.08.019

Cited by 142 publications

(52 citation statements)

References 227 publications

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“…Another practical concentration unit, commonly used in atomic-scale simulations, is the ratio of the number of He atoms in the bubble to the corresponding number of vacancies in the UO 2 matrix forming the bubble. This ratio is noted, n He /n vac in the following and is defined as: n He n vac = number of He atoms in a bubble number of U and O vacancies in a bubble (6) Namely, n He /n vac = 1, signifies that all the vacancies (either uranium or oxygen) are replaced with one He atom and a value of 1/3 corresponds herein to one He atom per Schottky defect. The He bubbles are created by removing UO 2 atoms within a sphere of radius r in the middle of the simulation box.…”

Section: Helium Nanobubblesmentioning

confidence: 99%

“…However, the exact role of the nanobubbles in this phenomena is still under debate. Physical integrity of He bubbles under self-irradiation is also an important question for fission gas release models [5] through re-solution rate coefficients [6]. To answer these questions one of the key ingredients is to describe accurately the He equation of state (EOS) reproducing the pressure-volume relationship.…”

Section: Introductionmentioning

confidence: 99%

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A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

Brutzel

Chartier

2019

Journal of Nuclear Materials

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Molecular dynamics simulations have been carried out to determine the equation of state of helium inside nanobubbles embedded into a UO 2 matrix. The parameters of the equation of state are fitted with the Brearley and MacInnes hard-sphere model based on the formalism of Carnahan-Starling used in fuel performance codes. This new equation of state takes into account the interactions between the surrounding UO 2 matrix and the helium atoms. Four nanobubble sizes (diameters: 1, 2, 5, and 10 nm) have been investigated over four temperatures (300, 500, 700, and 900 K) and for initial helium concentration inside the bubble ranging from 0.33 × 10 5 to 3.9 × 10 5 mol.m −3 (corresponding to helium-to-vacancy ratio of 0.3 to 3.3, respectively). We find that helium atoms are inhomogeneously distributed inside the bubble. A boundary layer of 1 nm thickness appears at the bubble surface in which helium atoms are more concentrated and diffuse into the UO 2 matrix. We also find a saturation concentration of the helium atoms that can be incorporated into the bubble. This concentration limit is equal to 1.6 helium atom per vacancy in UO 2 . It corresponds to an atomic volume of 7.8 × 10 −30 m 3 , which is almost half of the value proposed with the original Brearley and MacInnes model (13 × 10 −30 m 3 ). For this threshold concentration and for bubble of diameter higher than 5 nm, nano-cracks and dislocations appear at the bubble surface. However, experimental observation is needed to confirm this finding. We calculated the critical pressures inside the bubble which yields to this onset of crack in UO 2 . These critical pressures are in good agreement with those calculated with the Griffith criterion for brittle fracture.

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Section: Helium Nanobubblesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

Brutzel

Chartier

2019

Journal of Nuclear Materials

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“…As noted in Section 2.3.1, this assumption is made in order to reproduce fission gas release data from fuel rods with moderately high burnup that have been irradiated in commercial LWRs, although there is no direct evidence of significant gas release connected with the restructuring per se. In fact, some data suggest that the enhanced gas release observed for high burnup LWR fuel rods would emanate from material subjacent to the restructured rim zone, and hypotheses for this release exist [48]. Our modelling of fission gas release as a direct consequence of HBS formation may need to be reconsidered, if convincing evidence for these release mechanisms appears.…”

Section: Future Workmentioning

confidence: 93%

“…The key equations for fission gas production, transport and distribution applied in our model originate from the seminal work of Speight [45], and they are solved numerically by the method proposed by Forsberg and Massih [46] with later improvements by Hermansson and Massih [47]. A recent review of the subject can be found elsewhere [48].…”

Section: Fission Gas Production Transport and Distributionmentioning

confidence: 99%

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Modelling of fine fragmentation and fission gas release of UO₂ fuel in accident conditions

Jernkvist

2019

EPJ Nuclear Sci. Technol.

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In reactor accidents that involve rapid overheating of oxide fuel, overpressurization of gas-filled bubbles and pores may lead to rupture of these cavities, fine fragmentation of the fuel material, and burst-type release of the cavity gas. Analytical rupture criteria for various types of cavities exist, but application of these criteria requires that microstructural characteristics of the fuel, such as cavity size, shape and number density, are known together with the gas content of the cavities. In this paper, we integrate rupture criteria for two kinds of cavities with models that calculate the aforementioned parameters in UO2 LWR fuel for a given operating history. The models are intended for implementation in engineering type computer programs for thermal-mechanical analyses of LWR fuel rods. Here, they have been implemented in the FRAPCON and FRAPTRAN programs and validated against experiments that simulate LOCA and RIA conditions. The capabilities and shortcomings of the proposed models are discussed in light of selected results from this validation. Calculated results suggest that the extent of fuel fragmentation and transient fission gas release depends strongly on the pre-accident fuel microstructure and fission gas distribution, but also on rapid changes in the external pressure exerted on the fuel pellets during the accident.

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Research for the Safe Management of Nuclear Waste at Forschungszentrum Jülich: Materials Chemistry and Solid Solution Aspects

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Fission gas release from UO2 nuclear fuel: A review

Cited by 142 publications

References 227 publications

A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

Modelling of fine fragmentation and fission gas release of UO₂ fuel in accident conditions

Research for the Safe Management of Nuclear Waste at Forschungszentrum Jülich: Materials Chemistry and Solid Solution Aspects

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Fission gas release from UO2 nuclear fuel: A review

Cited by 142 publications

References 227 publications

A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

Modelling of fine fragmentation and fission gas release of UO2 fuel in accident conditions

Research for the Safe Management of Nuclear Waste at Forschungszentrum Jülich: Materials Chemistry and Solid Solution Aspects

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Modelling of fine fragmentation and fission gas release of UO₂ fuel in accident conditions