Oxidation effect on steel corrosion and thermal loads during corium melt in-vessel retention

International audienceDuring a severe accident with core meltdown, the in-vessel molten core retention is challenged by the vessel steel ablation due to thermal and physicochemical interaction of melt with steel. In accidents with oxidizing atmosphere above the melt surface, a low melting point UO2+x-ZrO 2-FeOy corium pool can form. In this case ablation of the RPV steel interacting with the molten corium is a corrosion process. Experiments carried out within the International Scientific and Technology Center's (ISTC) METCOR Project have shown that the corrosion rate can vary and depends on both surface temperature of the RPV steel and oxygen potential of the melt. If the oxygen potential is low, the corrosion rate is controlled by the solid phase diffusion of Fe ions in the corrosion layer. At high oxygen potential and steel surface layer temperature of 1050 °C and higher, the corrosion rate intensifies because of corrosion layer liquefaction and liquid phase diffusion of Fe ions. The paper analyzes conditions under which corrosion intensification occurs and can impact on in-vessel melt retention (IVR). © 2014 The Authors

Corrosion of Vessel Steel During its Interaction with Molten Corium - Part 2 Model Development

An experimental examination of the cooled vessel steel corrosion during the interaction with molten corium is presented. The experiments have been conducted test facility and followed up with physico-chemical and metallographic analyses of melt samples and coriumspecimen ingots. The results discussed in the first part of the paper have revealed specific corrosion mechanisms for air and inert atmosphere above the melt. Models have been proposed based on this information and approximate curves constructed for the estimation of the corrosion rate or corrosion depth of vessel steel in conditions simulated by the experiments.JRC.E.2-Hot cell

Corrosion of Vessel Steel During its Interaction with Molten Corium - Part 1 Experimental

This paper is concerned with corrosion of a cooled vessel steel structure interacting with molten corium in air and neutral (nitrogen) atmospheres during an in-vessel retention scenario. The data on corrosion kinetics at different temperatures on the heated steel surface, heat flux densities and oxygen potential in the system are presented. The post-test physico-chemical and metallographic analyses of melt samples and the corium–specimen ingot have clarified certain mechanisms of steel corrosion taking place during the in-vessel melt interaction.JRC.E.2-Hot cell

Corrosion of Vessel Steel during its Interaction with Molten Corium. Part 2. Model Development.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe

Corium phase equilibria based on MASCA, METCOR and CORPHAD results

Experimental data on component partitioning between suboxidized corium melt and steel in the in-vessel melt retention (IVR) conditions are compared. The data are produced within the OECD MASCA program and the ISTC CORPHAD project under close-to-isothermal conditions and in the ISTC METCOR project under thermal gradient conditions. Chemical equilibrium in the U-Zr-Fe(Cr,Ni,...)-O system is reached in all experiments. In MASCA tests the molten pool formed under inert atmosphere has two immiscible liquids, oxygen-enriched (oxidic) and oxygen-depleted (metallic), resulting of the miscibility gap of the mentioned system. Sub-system data of the U-Zr-Fe(Cr,Ni,...)-O phase diagram investigated within the ISTC CORPHAD project are interpreted in relation with the MASCA results. In METCOR tests the equilibrium is established between oxidic liquid and mushy metallic part of the system. Results of comparison are discussed and the implications for IVR noted. © 2008

Oxidation effects during corium melt in-vessel retention

International audienceIn the in-vessel corium retention studies conducted on the Rasplav-3 test facility within the ISTC METCOR-P project and OECD MASCA program, experiments were made to investigate transient processes taking place during the oxidation of prototypic molten corium. Qualitative and quantitative data have been produced on the sensitivity of melt oxidation rate to the type of oxidant, melt composition, molten pool surface characteristics. The oxidation rate is a governing factor for additional heat generation and hydrogen release; also for the time of secondary inversion of oxidic and metallic layers of corium molten pool. © 201

Experimental Study of Interactions Between Suboxidized Corium and Reactor Vessel Steel

One of the critical factors in the analysis of in-vessel melt retention is the vessel strength. It is, in particular, sensitive to the thickness of intact vessel wall, which, in its turn, depends on the thermal conditions and physicochemical interactions with corium. Physicochemical interaction of prototypic UO2-ZrO2-Zr corium melt and VVER vessel steel was examined during the 2nd Phase of the ISTC METCOR Project.JRC.E.2-Hot cell

Experimental study of transient phenomena in the three-liquid oxidic-metallic corium pool

International audienceNon-steady physicochemical phenomena in the three-liquid molten pool of prototypic corium are studied in the context of in-vessel melt retention problem. Experiments are made on the Rasplav-3 test facility within the CORDEB program. Structure of the initial molten pool consists of the surface light melt of molten steel, the intermediate layer of oxidic melt separated from steel melt by the crust; and the bottom layer of heavy metallic melt. It is determined that the three-layer pool structure can stay stable for a certain period of time, but the partitioning of steel and oxidic melt components through the crust brings the possibility of transformation of the three-layer pool to a two-layer structure. © 2018 Elsevier B.V

Effect of temperature gradient on chemical element partitioning in corium pool during in-vessel retention

International audienceThe paper presents some results of the ISTC (International Science and Technology Center)-financed project ‘Investigation of Corium Melt Interaction with NPP Reactor Vessel Steel’ (METCOR). In the METCOR experiments the metallic phase of a two-liquid system was produced by the interaction between hot suboxidized corium and cooled VVER vessel steel, with the steel being corroded. Models of corrosion mechanisms in the considered conditions are used to systematize data on the limiting temperature of corrosion/(dissolution) of the vessel steel. A considerable influence of thermal gradient conditions is shown, which has to be taken into account in the analysis of molten pool behaviour. © 2017 Elsevier B.V