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Phase Relations in Corium Systems

#3813


Phase Relations in Corium Systems

Tech Area / Field

  • FIR-EXP/Experiments/Fission Reactors

Status
8 Project completed

Registration date
24.08.2007

Completion date
17.10.2012

Senior Project Manager
Tocheny L V

Leading Institute
Research Institute of Technology, Russia, Leningrad reg., Sosnovy Bor

Supporting institutes

  • Joint Institute for High Temperatures RAS, Russia, Moscow

Collaborators

  • Forschungszentrum Karlsruhe GmbH, Germany, Karlsruhe\nCEA / Institut de Radioprotection et de Surete Nucleaire, France, Saint-Paul-lez-Durance\nEuropean Commission / Joint Research Center / Institute for Transuranium Elements, Germany, Karlsruhe\nAREVA / Areva NP GmbH, Germany, Erlangen\nCEA / DEN / Direction du Soutien Nucleaire Industriel, France, Gif-sur-Yvette Cedex

Project summary

The general objective of the proposed project is to ensure NPP reactor safety in case of a severe accident with core meltdown, and optimal designing of the melt localization devices by means of enhancing precision of thermodynamic calculations of phase conditions and transformations in multicomponent corium systems.

Specific subject of the project is the experimental investigation of phase diagrams of oxidic and metal-oxidic corium systems which form as the result of core meltdown and interaction of melt with construction and structural materials of the reactor, concrete shaft and core catcher.

The modern practice of justifying safety of reactor facilities in case of a severe accident is to a significant extent based on the coupled thermalhydraulic and thermodynamic modeling of the involved high-temperature process. Thermodynamic modeling of multicomponent melts employs specialized numerical codes (e.g., GEMINI-2) and program-specific databases (e.g., NUCLEA-06) created on the basis of experimental data the volume of which is still insufficient for reliable reactor application.

A significant number of investigations was devoted to experimental studies of corium phase diagrams. Among the recent ones there should be mentioned such EU projects as ECOSTAR, COLOSS, ENTHALPY, CIT and SARNET (the proposed project performers participated in the three former ones), as well as the ISTC project # 1950.2 CORPHAD, entirely realized by the proposed project performers.

For instance, the said European projects have helped to optimize the following diagrams: UO2-ZrO2; UO2-ZrO2-FeO-Cr2O3; Fe2O3-ZrO2; Fe2O3-UO2. The CORPHAD project (completed in November 2006) had yielded new data on phase diagrams of other systems of relevance to the reactor application, and concomitant information of importance for understanding mechanisms of physicochemical processes and for increasing precision of modeling thermodynamics and thermochemistry of multicomponent corium systems:

  • The binary oxidic systems UO2-FeO, ZrO2-FeO, Fe2O3(Fe3O4)-SiO2 and Fe3O4-SiO2 have been investigated. Tliq/Tsol concentration dependencies within a broad range have been determined along with the eutectic point coordinates and the limits of components’ solubility in the solid phase. The obtained results allowed optimizing the NUCLEA database.
  • A limited domain of the SiO2-UO2 binary system has been studied, the miscibility gap boundary and monotectic temperature evaluated.
  • A study has been performed to determine coordinates of eutectic points of the ternary oxidic system UO2±x-ZrO2-FeOy under low oxyge potential of the system (in an inert atmosphere) and in the oxidizing atmosphere (air).
  • Tliq and Tsol, as well as compositions of the liquids coexisting in the miscibility gap have been determined for a range of compositions of ternary metal-oxidic systems U-Zr-O, Zr-Fe-O and U-Fe-O in the low oxygen concentrations domain.
  • Tliq has been determined for the composition of a multicomponent prototypic corium mixture specified by the collaborators.
  • Extensive studies aimed at developing thermal analysis methodology have been carried out.
  • The facilities fit for realization of new analytical methods have been created.

The newly invited participants from IVT RAS have also developed a new method and designed a facility for phase diagram studies by means of laser-induced heating (Laser pulse method), the application of which has yielded new experimental data on phase diagrams of UO2-ZrO2, UO2-Zr and U-O.

The obtained results were used for optimizing the NUCLEA database and raising precision of modeling in-vessel thermodynamic behaviour of corium during a severe accident with core melting. The main results of the preformed studies have been published in the following papers and presentations:

  • Lopukh D., Bechta S., Pechenkov A., Vitol S., Hellmann S., Fischer M., Froment K., Duret B., Seiler J. New Experimental Results on the Interaction of Molten Corium with Core Catcher Material // 8th International Conference on Nuclear Engineering, ICONE-8179, April 2-6, 2000, Baltimore, MD, USA.
  • Mezentseva L.P., Popova V.F., Almjashev V.I., Lomanova N.A., Ugolkov V.L., Bechta S.V., Khabensky V.B., Gusarov V.V. Phase and chemical transformations in the SiO2-Fe2O3(Fe3O4) system at different partial pressure of oxygen // J. of Inorganic Chemistry, 2006, V. 51, No. 1, p. 1-8.
  • Bechta S.V., Krushinov E.V., Almjashev V.I., Vitol S.A., L.P., Petrov Yu.B., Lopukh D.B., Khabensky V.B., Barrachin M., Hellmann S., Gusarov V.V. Phase relations in the ZrO2-FeO system// J. of Inorganic Chemistry, 2006, V. 51, No. 2, p. 367-374.
  • Bechta S.V., Krushinov E.V., Almjashev V.I., Vitol S.A., Mezentseva L.P., Petrov Yu.B., Lopukh D.B., Khabensky V.B., Barrachin M., Hellmann S., Froment K., Fischer M., Tromm W., Bottomley D., Defoort F., Gusarov V.V., Phase diagram of the ZrO2-FeO system // J. Nucl. Mater., 348 (2006), 114-121.
  • Mezentseva L.P., Popova V.F., Almjashev V.I., Lomanova N.A., Ugolkov V.L., Bechta S.V., Khabensky V.B., Barrachin M., Hellmann S., Gusarov V.V. Phase diagrams of the SiO2-Fe2O3(Fe3O4) systems in different gas atmospheres // J. Europ. Ceram. Soc., 2006, in press.
  • Bechta S.V., Khabensky V.B., Granovsky V.S., Krushinov E.V., Vitol S.A., Gusarov V.V., Almjashev V.I., Mezentseva L.P., Petrov Yu.B., Lopukh D.B., Fischer M., Bottomley D., Tromm W., Barrachin M., Altstadt E., Piluso P., Fichot F., Hellmann S., Defoort F., CORPHAD and METCOR ISTC projects // The first European Review Meeting on Severe Accident Research (ERMSAR-2005), Aix-en-Provence, France, 14-16 November, 2005.
  • Bechta S.V., Krushinov E.V., Almjashev V.I., Vitol S.A., Mezentseva L.P., Lopukh D.B., Petrov Yu.B., Khabensky V.B., Barrachin M., Hellmann S., Froment K., Fischer M., Tromm W., Bottomley D., Defoort F., Gusarov V.V., Phase diagram of the UO2-FeO1+x system // J. Nucl. Mater., 362 (2007) 46-52
  • Bechta S.V., Krushinov E.V., Almjashev V.I., Vitol S.A., Mezentseva L.P., Petrov Yu.B., Lopukh D.B., Lomanova N.A., Khabensky V.B., Barrachin M., Hellmann S., Froment K., Fischer M., Tromm W., Bottomley D., Gusarov V.V. Phase transformations in the binary section of the UO2-FeO-Fe system // Radiochemistry, 2007, V. 49, No. 1, p. 20-24.
  • Manara D., Sheindlin M. and Levis M. Advances in Measurements of the Melting Transition in Non-Stoichiometric UO2 // Int. J. of Thermophysics, vol. 25, No. 2 (2004), p. 533-545.
  • Manara D., Pflieger R. and Sheindlin M. Advances in the Experimental Determination of the Uranium – Oxygen Phase Diagram at High Temperature // Int. J. of Thermophysics, vol. 20, ¹ 4, July 2005, p. 1193-1206.
  • Pflieger R., Sheindlin M. And Colle J.-Y., Thermodynamics of Refractory Nuclear Materials Studied by Mass Spectrometry of Laser-Produced Vapors // Int. J. of Thermophysics, vol. 26, ¹ 4, July 2005, p. 1075-1093.

At the same time, the large number of the little-investigated systems, laboriousness and complexity of performing tests with and posttest analyses of the high-temperature corium, as well as the limited time for realization of the ISTC CORPHAD project prevented a comprehensive study of phase diagrams of the systems that form during a severe accident, have relevance to the reactor application and are used for justifying safety of reactor facilities.

Among these little-studied systems are:

  • Binary and ternary oxidic systems (CaO-UO2, CaO-FeO, SiO2-UO2, UO2-FeO-SiO2, UO2-FeO-CaO, ZrO2-FeO-SiO2, ZrO2-FeO-CaO) containing components of concretes and sacrificial materials, i.e. of importance for modeling the interaction of corium with materials of the concrete shaft and core catcher at the ex-vessel stage of a severe accident development. The SiO2–containing systems should be specially mentioned, as their high viscosity and low electroconductivity make their experimental investigation problematic. Still, they are very important for modeling the ex-vessel corium from a series of power reactors, including such modern ones as EPR.
  • Metal-oxidic systems U-Zr-Fe-O with different concentrations of components, especially in the miscibility gap.
  • Multicomponent mixtures representing prototypic ex-vessel corium.

The said systemns are to be studied in the proposed project.

The main results of the project should be the following experimentally determined main characteristics:

  • Tliq and Tsol concentration dependencies;
  • Coordinates of characteristic points, such as eutectic, dystectic, etc.;
  • Limits of components solubility in the solid phase;
  • Compositions of the liquids coexisting in the miscibility gap.

The data generated in the course of the project implementation will be used for:
  • Replenishing databases with the missing or specified experimental information concerning phase diagrams of the oxidic and metal-oxidic corium systems;
  • Refining the calculated thermodynamic models, including the sphere of modeling stratification and the quasiequilibrium states under thermogradient conditions;
  • Verifying thermodynamic numerical codes that model phase diagrams of multicomponent systems which form as the result of interaction between the molten core and structural and construction materials of the reactor, concrete shaft and core catcher.;
  • Justifying and enhancing safety of the existing and new NPP designs with VVER, PWR and BWR reactors.


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