New modelling of the U–O–Zr phase diagram in the hyper-stoichiometric region and consequences for the fuel rod liquefaction in oxidising conditions

Barrachin, M.; Chevalier, P.Y.; Cheynet, Bertrand; Fischer, Evelyne

doi:10.1016/j.jnucmat.2008.02.003

Cited by 32 publications

(8 citation statements)

References 40 publications

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“…27 This indicates that the particle was locally heated higher than ~2800 K. The melting temperature can be even lower than 2800 K in corium, which is a lava-like melt of the fuels, because the liquidus and solidus temperatures of the hyperstoichiometric U oxides (up to UO 2.21 ) decrease to as low as 2800 K and 2400 K, respectively. 30 In addition, the wide range in the composition of U-Zr oxides (U/(U+Zr) = 0.14-0.91), indicates that the melt did not form a large-scale pool of homogeneous composition. Rather, the U-Zr-oxide eutectic occurred heterogeneously at the micron scale due to spatial variations in the chemistry.…”

Section: Formation Processes Of the Reactor Debris Fragmentsmentioning

confidence: 99%

Uranium Dioxides and Debris Fragments Released to the Environment with Cesium-Rich Microparticles from the Fukushima Daiichi Nuclear Power Plant

Ochiai

Imoto

Suetake

et al. 2018

Environ. Sci. Technol.

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Trace U was released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) during the meltdowns, but the speciation of the released components of the nuclear fuel remains unknown. We report, for the first time, the atomic-scale characteristics of nanofragments of the nuclear fuels that were released from the FDNPP into the environment. Nanofragments of an intrinsic U-phase were discovered to be closely associated with radioactive cesium-rich microparticles (CsMPs) in paddy soils collected ∼4 km from the FDNPP. The nanoscale fuel fragments were either encapsulated by or attached to CsMPs and occurred in two different forms: (i) UO nanocrystals of ∼70 nm size, which are embedded into magnetite associated with Tc and Mo on the surface and (ii) Isometric (U,Zr)O nanocrystals of ∼200 nm size, with the U/(U+Zr) molar ratio ranging from 0.14 to 0.91, with intrinsic pores (∼6 nm), indicating the entrapment of vapors or fission-product gases during crystallization. These results document the heterogeneous physical and chemical properties of debris at the nanoscale, which is a mixture of melted fuel and reactor materials, reflecting the complex thermal processes within the FDNPP reactor during meltdown. Still CsMPs are an important medium for the transport of debris fragments into the environment in a respirable form.

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Section: Formation Processes Of the Reactor Debris Fragmentsmentioning

confidence: 99%

Uranium Dioxides and Debris Fragments Released to the Environment with Cesium-Rich Microparticles from the Fukushima Daiichi Nuclear Power Plant

Ochiai

Imoto

Suetake

et al. 2018

Environ. Sci. Technol.

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“…The laser-heating radiation spectroscopy technique presented here is recognized as an innovative and effective method for the investigation of very high-temperature and melting behavior of refractory materials 15 , 16 . Thanks to its remote and almost container-less nature, it is particularly suited for the experimental study of radioactive nuclear materials and the simulation of core meltdown accidents in NPPs, as shown by the example results presented here.…”

Section: Discussionmentioning

confidence: 99%

Laser-heating and Radiance Spectrometry for the Study of Nuclear Materials in Conditions Simulating a Nuclear Power Plant Accident

Manara

Soldi

Mastromarino

et al. 2017

JoVE

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Major and severe accidents have occurred three times in nuclear power plants (NPPs), at Three Mile Island (USA, 1979), Chernobyl (former USSR, 1986) and Fukushima (Japan, 2011). Research on the causes, dynamics, and consequences of these mishaps has been performed in a few laboratories worldwide in the last three decades. Common goals of such research activities are: the prevention of these kinds of accidents, both in existing and potential new nuclear power plants; the minimization of their eventual consequences; and ultimately, a full understanding of the real risks connected with NPPs. At the European Commission Joint Research Centre's Institute for Transuranium Elements, a laser-heating and fast radiance spectro-pyrometry facility is used for the laboratory simulation, on a small scale, of NPP core meltdown, the most common type of severe accident (SA) that can occur in a nuclear reactor as a consequence of a failure of the cooling system. This simulation tool permits fast and effective high-temperature measurements on real nuclear materials, such as plutonium and minor actinide-containing fission fuel samples. In this respect, and in its capability to produce large amount of data concerning materials under extreme conditions, the current experimental approach is certainly unique. For current and future concepts of NPP, example results are presented on the melting behavior of some different types of nuclear fuels: uranium-plutonium oxides, carbides, and nitrides. Results on the high-temperature interaction of oxide fuels with containment materials are also briefly shown.

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“…The thermodynamic Calphad modelling of the U-O-Zr phase diagram is available in different papers [19,62,63]. An important conclusion of these works is that the overall topology of the phase diagram is thermodynamically assessed over the whole temperature range 1000-2800 • C in the hypo-stoichiometric region.…”

Section: Intermediate Temperature Regime (1450-2200 • C)mentioning

confidence: 99%

“…At temperature above 2300 • C (some papers mentioned temperatures slightly below 2300 • C [19,20]), a (partial) relocation of the fuel rod materials occurs resulting in the formation of a more or less large molten pool. This is the third regime.…”

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confidence: 99%

Corium Experimental Thermodynamics: A Review and Some Perspectives

Barrachin

2021

Thermo

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More than 30 years ago a specialist meeting was held at Joint Research Center Ispra (Italy) from 15 to 17 January 1990 to review the current understanding of chemistry during severe accidents in light water reactors (LWR). Let us consider that, at the end of the 1980s, thermodynamics introduced in the severe accident codes was really poor. Only some equilibrium constants for a few simple reactions between stoichiometric compounds were used as well as some simple correlations giving estimates of solidus and liquidus temperatures. In the same time, the CALPHAD method was developed and was full of promise to approximate the thermodynamic properties of a complex thermochemical system by the way of a critical assessment of experimental data, a definition of a simple physical model and an optimisation procedure to define the values of the model parameters. It was evident that a nuclear thermodynamic database had to be developed with that new technique to obtain quite rapidly prominent progress in the knowledge of thermochemistry in the severe accident research area. Discussions focused on the important chemical phenomena that could occur across the wide range of conditions of a damaged nuclear plant. The most pressing need for improved chemical models is identified with condensed phase mixtures to model the corium progression. This paper reviews more than 30 years of experimental data production in the field of corium thermodynamics. This work has been conducted through multiple international programs (EURATOM, ISTC, OECD) as well as through more specific studies conducted at the national scale. This research has been capitalised in specific databases such as NUCLEA and TAF-ID, databases developed at IRSN and at CEA, respectively, and are now used in degradation models of the severe accident simulation codes. This research is presented in this paper. In the conclusion, we outline the research perspectives that need to be considered in order to address today’s and tomorrow’s issues.

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New modelling of the U–O–Zr phase diagram in the hyper-stoichiometric region and consequences for the fuel rod liquefaction in oxidising conditions

Cited by 32 publications

References 40 publications

Uranium Dioxides and Debris Fragments Released to the Environment with Cesium-Rich Microparticles from the Fukushima Daiichi Nuclear Power Plant

Uranium Dioxides and Debris Fragments Released to the Environment with Cesium-Rich Microparticles from the Fukushima Daiichi Nuclear Power Plant

Laser-heating and Radiance Spectrometry for the Study of Nuclear Materials in Conditions Simulating a Nuclear Power Plant Accident

Corium Experimental Thermodynamics: A Review and Some Perspectives

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