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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 (CORPHAD)

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
02.08.2000

Completion date
16.09.2002

Senior Project Manager
Rudneva V Ya

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

Collaborators

  • CEA / 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

Project summary

The ultimate goal of the proposed project is the nuclear reactor safety enhancement in case of a severe accident involving the core meltdown. The objectives of the project are:
- Experimental studies for constructing new and improving currently-used phase diagrams of oxide and mixed corium systems, including the components of reactor control systems, concrete shaft, and core catcher (with sacrificial and protective oxides).
- Experimental investigation of the transition kinetics between different melt steady states, to improve physic-chemistry models and to estimate kinetic coefficients.
- Verification tests to study the interaction of melt with construction and refractory materials, to develop integral calculation codes.
- Development of an advanced numeric code to predict phase diagrams and certain physic-chemical properties of n-component corium, mixed with interaction products.
- Updating available databases used in phase-diagram calculations and describing physic-chemical processes in corium melts.
- Development of an improved-interface numeric code to predict the behavior of various materials in contact with corium in a wide temperature range.

The currently used numeric codes (most widely used are THERMOCALC and GEMINI) and their databases are applied for modeling physico-chemical corium characteristics and in the theoretical justification of NPP safety in case of a severe accident with core meltdown.

However, these numeric codes require further development. This involves additional experimental studies for examining thermodynamic characteristics of compounds at different phases to add the components currently missing into the database. Besides, the molten corium crystallization, or its solid components melting and dissolution is a non-equilibrical process, in which the system phase parameters change in time, so experimental evaluation of kinetics coefficients is necessary to refine the numeric physico-chemical models.

The currently available databases on binary and ternary oxidic systems and binary alloys have different contents and usage possibilities. Very well-known are TDB CR used for basic reactor calculations; PDEC (Phase Diagrams for Ceramics); Bard (Binary Alloys Phase Diagrams); TAPD CD; IVTANTERMO and others.

The Project will make a significant contribution to the well-established TDB CR phase diagram database, used in reactor calculations, using:


· new data from experiments mostly with uranium-bearing systems produced on the RASPLAV-2 installation at NITI and from other test facilities of SPbGTI, SPbGETU and ISC RAS;
· published data including Russian reference books and other sources previously unavailable for all the above mentioned databases.

Experimental phase composition study of radioactive (mostly uranium-bearing) and non-radioactive mixtures at different temperatures is one of the fundamental Project objectives. Mixture compositions and temperature ranges will be chosen by the joint decision of Project team and collaborators. The following parameters will be determined during the experimental investigation of 2- and 3- component diagrams: solidus temperature (TSol), liquidus temperature (TLiq), eutectic melt compositions and melting temperature, concentration and temperature regions of melt stratification. Additionally, chemical reaction rates during interaction will be evaluated at the transition from one equilibrical state to another, interaction energy parameters and release of gaseous species.

The obtained experimental data will be included into appropriate databases, used to improve physicochemical models and for computer code verification. If the collaborators consider it advisable, prior to the scheduled experimental program, the pretest forecast calculations will be made, using available computer codes (THERMOCALC and GEMINI) in order to estimate the prediction accuracy of calculation codes.

A significant part of experimental studies will be conducted on RASPLAV - 2 installation, which has been successfully operated for 13 years. In 1997 the ISTC project 064-094 "NPP Reactor Core Catcher Designed on the Basis of ZrO2 Concrete" was completed, in which it was engaged for studying the interaction between uranium-bearing corium and zirconia concrete. Since April 1999 it has been used in the ISTC project 833-99 "Investigation of Corium Melt Interaction With NPP Reactor Vessel Steel", which will be completed in the end of 2000.

To produce corium melt in the RASPLAV-2 facility an original technology of induction melting in a cold crucible (IMCC) is employed. Presence of a solid phase (lining crust) between the melt and crucible provides conditions for high rates of melt superheating; oxidizing and inert above-melt atmosphere; does not restrict test duration, and has some other advantages. IMCC installations are successfully operated at NITI and, SPbGETU for obtaining data on phase diagrams.

The experimental studies of high-temperature phase diagrams for oxide non-radioactive systems will partially be conducted at the installations of ISC RAS and SPbGTI. There phase diagrams at up to 2573 K have been studied for over 50 years using Galakhov methods, differential thermal analysis and visual polythermal analysis enabling to get highly accurate and credible data.

Numerous phase diagrams produced at the facilities of ISC RAS were included into all contemporary reference books on the phase diagrams of oxide systems ("Diagrams of refractory oxide systems", "Phase diagrams for Ceramists", which proves the high adequacy and reliability of results obtained there.

The proposed project aims to establish a calculation complex with improved service options, to construct phase and fusibility diagrams for ternary and more complex systems in non-equilibrium conditions, expressed in quasi-equilibrium approximation, using the Radischev-Perelman optimal projection method.

The behavior forecast for materials in contact with corium is planned using the verified kinetic models.

If the Project proposal is accepted the scope and matrix of experiments will be determined on agreement with collaborators to meet the requirements to the data integrated into international programs.

The proposed Project involves researchers and engineers (more than 60 %) previously engaged in the development of military technologies, so it topically belongs to the project category supported by ISTC.


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