De-mixing of Corium During Spreading
- Department of Energy Systems and Energy Economics, Ruhr- University Bochum (Germany)
Especially, for the next generation of nuclear power plants the mitigation of possible severe accidents has been taken into account in the design phase. Core catcher concepts are discussed (e.g. for the European Pressurized Water Reactor EPR) in order to reduce containment threat even under the very unlikely conditions of core melt down and subsequent ex-vessel release of molten material. Regarding the EPR, it is foreseen to let the core melt spread onto a flat area in order to provide for controlled cooling conditions to insure the integrity Of the containment vessel. Regarding the investigation and validation of the core catcher concept, experimental programs focusing on melt flow conditions and coolability were initiated. Furthermore, to translate the test results to real boundary conditions, computer codes which are capable to adequately model the relevant phenomena are made available. So far, the outcomes of the studies generally lead to a broad knowledge concerning the melt spreading phenomena. Nevertheless, uncertainties concerning the modeling of melt spreading still exist. Among these, the separation kinetics of the melt, mainly in a metallic and an oxidic phase, is not understood in every detail yet. Such a separation is observed in practically all experiments dealing with core melts including metallic and oxidic components and most probably has got a strong influence on the spreading behavior of molten corium, since important properties, e.g. viscosity, emissivity as well as liquidus and solidus temperature, are dependent on the fluid composition to a very large extend. To consider a de-mixing flow of a metallic and oxidic melt in codes a large computational effort would be necessary. Since it is believed that the flow during spreading is turbulent enough, in all commonly known spreading codes the melt is regarded as being completely mixed during the whole spreading process. Eventually, the influence of stratification on the temperature is accounted for by using different heat transport models for the bottom and the top of the melt. Even though this approach seems to be reasonable, for a more detailed verification of it the stratification behavior of melts will be discussed in the work on hand for the beginning of the spreading process, since here the subsequent cooling behavior during spreading will be determined. For this purpose a simplified approach based on the lattice gas method is used. In this method, the use of non-distinguishable particles moving on a fixed lattice allows for a memory effective programming and, hence, the simulation of a transient flow of two immiscible phases. The basic theory will be discussed briefly and example calculations will be presented in the paper. Up to now, the approach is developed, but a sufficient data basis to use it is lacking and will be provided in the near future. (authors)
- Research Organization:
- American Nuclear Society, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
- OSTI ID:
- 21167875
- Resource Relation:
- Conference: ICAPP'02: 2002 International congress on advances in nuclear power plants, Hollywood, FL (United States), 9-13 Jun 2002; Other Information: Country of input: France; 11 refs
- Country of Publication:
- United States
- Language:
- English
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