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Phase Diagrams for Corium

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Phase Diagrams for Multicomponent Systems Containing Corium and Products of its Interaction with NPP Materials

Tech Area / Field

  • FIR-MAT/Materials and Materials Conversion/Fission Reactors
  • FIR-MOD/Modelling/Fission Reactors
  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors

Status
8 Project completed

Registration date
16.07.2002

Completion date
16.05.2008

Senior Project Manager
Rudneva V Ya

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

Collaborators

  • CEA / Institut de Radioprotection et de Surete Nucleaire, France, Saint-Paul-lez-Durance\nInstitut für Kern und Energietechnik, Germany, Karlsruhe\nEuropean Commission / Joint Research Center / Institute for Transuranium Elements, Germany, Karlsruhe\nCEA / Direction des Technologies Avancees Centre d'Etudes et de Recherches sur les Materiaux/Laboratoire de la Solidification et de Ses Procedes, France, Grenoble\nArgonne National Laboratory (ANL) / Reactor Engineering Division, USA, IL, Argonne\nFramatome ANP GmbH, Germany, Erlangen

Project summary

The main project objective is to increase the PWR and BWR safety level in case of severe accidents entailing core degradation and melting. The specific subject of the proposed project is to experimentally determine phase diagrams for the multi-component corium systems and for products of its interaction with NPP materials.

One of the ways to safely manage the PWR or BWR severe accident is to localize the molten core inside the containment and to keep the ex-containment release of volatile and low-volatile fission products within safe levels.

Currently two severe accident management approaches are accepted for the operating and future PWR and BWR reactors.

1. For the medium-capacity reactors the in-vessel corium retention can be efficient if outside water cooling is possible.
2. Higher-capacity reactors are provided with an ex-vessel core catcher, where the molten core is stabilised and cooled.
The numeric modelling of interaction between the molten core and construction/structural materials of the reactor unit, concrete pit and core catcher requires adequate phase diagrams of corium and corium-based mixtures. The calculations of phase diagrams of multi-component systems use thermodynamic computer codes and corresponding databases, incorporating the experimental data.

At present, the experimental data on phase diagrams of realistic corium systems are still limited, which is explained by the following:

· Experimental studies with a high-temperature (up to 3300 K), chemically active, molten corium are very complicated, only a limited number of currently available experimental facilities can provide the required conditions.


· Newly developed PWR and BWR units employ advanced construction and structural materials, including sacrificial material used in severe accident management.
· New phenomena, specific for the in- and ex-vessel stages of a severe accident have been identified. They influence the molten pool structure and characteristics, e.g. the U and Zr extraction from the sub-oxidised corium melt by the molten steel, as it was observed on the “Rasplav-3” test facility during the test of the OECD/MASCA project. Although the phenomenon had been predicted by [Hofmann, 1976], [Gueneau, 1999] and [Parker, 1982], further detailed investigations are needed.
· National norms and regulations of some countries impose certain restrictions on activities in which radioactive materials are handled.
Due to the above-mentioned reasons, the necessity for additional experimental data on phase diagrams is obvious, which is the key objective of the CORPHAD Project.

The main phase diagram studies of uranium-bearing systems will be performed on the NITI experimental facilities, where realistic reactor conditions can be provided. These experimental installations have been successfully operated during the last 14 years. In 1994 - 1997 NITI used them in the ISTC Project 064-94 “Zirconia-based core catcher”; from April 1999 till December 2000 they were employed in the ISTC Project 833-99 “Investigation of corium melt interaction with NPP reactor vessel steel”. From 2001 until present time the experimental studies within OECD/MASCA project are carried out there.

The proposed work will be implemented with the participation of experts from St. Petersburg Technological University (SPbGTU), Research Institute of Silicate Chemistry of the Russian Academy of Sciences (ISC RAS) and St. Petersburg Electrotechnical University (SPbGETU).

The proposed project will use the expertise of highly-qualified specialists, who study severe accidents, interaction of high-temperature corium with different materials, physical chemistry and non-metallic material technologies; they have been authors and co-authors of many research papers and reference books, written on the subject of the proposed project. There are 5 professors and 8 doctors of sciences in the project team.


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