Interface temperature between solid and liquid corium in severe accident situations: A comprehensive study of characteristic time delay needed for reaching liquidus temperature

• Published in: Nuclear engineering and design 2010-08, Vol.240 (8), p.1975-1985
• Main Authors: Combeau, H., Appolaire, B., Seiler, J.M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Controled nuclear fusion plants; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Fuels; Installations for energy generation and conversion: thermal and electrical energy; Mass transfer; Nuclear fuels; Nuclear power generation; Nuclear reactor components; Pools; Segregations; Silicon dioxide; Solidification; Time delay
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2010.04.004

T liquidus was proposed as the interface temperature ( Seiler and Froment, 2000), for various severe accident situations for thermalhydraulic steady state. This proposal was made on the basis of the analysis of solidification front stability in thermalhydraulic steady state for volumetrically heated corium pools and was extended to reactor transients with slow solidification rates that are controlled by the long-term decrease in residual power. The conclusions were corroborated by prototypic corium and variable solidification rates obtained by experimental approaches ( Dauvois et al., 2000; Journeau et al., 2003) for corium containing small amounts of silica or none at all. When the concentration in silica increases (approximately above 10 wt%), it was concluded from the experiments that a plane-front situation could not be obtained. The present work offers a theoretical approach to the maximum time delay that is necessary for mass transfer and full phase-segregation in volumetrically heated liquid pools bounded by a crust. It is concluded that full segregation is obtained for in-vessel situations within time delays that are shorter or of the same order of magnitude as the characteristic time for the corium pool to form and evolve to a quasi-steady-state situation. The characteristic time delay for mass transfer associated with simulant material experiments is also determined. Phase segregation can also be obtained for corium–concrete interaction, provided that the silica content is less than approximately 10 wt%. However in the latter case, more complex phenomena occur at the interface due to the interaction with sparging gas (such as porous medium formation) which requires a different model approach.