CSNI/NEA RASPLAV Seminar 2000, 14-15 November 2000, Munich, Germany - Executive Summary

The objective of the RASPLAV Project was to provide data on the behaviour of molten core materials on the RPV lower head under severe accident conditions, and to assess the possible physicochemical interactions between molten corium and the vessel wall. Data were also obtained to confirm heat transfer modelling for a large convective corium pool within the lower head. The project consisted of the following components: - To provide data from large-scale integral experiments on the behaviour and interactions of prototypic core-melt materials within the lower head; - To perform small-scale corium experiments to measure the thermo-physical properties (density, electrical and thermal conductivity, viscosity, etc.) required for performing and interpreting the integral (large-scale) tests; - To determine the uncertainties introduced by using non-prototypic conditions and materials by means of the small-scale corium experiments; - To carry out the molten-salt experiments with the following objectives: - To study heat transfer processes in the melt; - To justify the choice of procedures for large-scale experiments, such as the heating method; To develop an understanding of relevant phenomena, such as crust formation, and non-eutectic materials behaviour; - To develop computer tools and models for analysis of results from the large-scale integral tests and the supporting small-scale experiments. During the first phase of the RASPLAV Project (1994-97) the large-scale experiments demonstrated clearly that behaviour of corium melts differed from that of simulant materials. Under certain conditions, the corium would separate into two layers that were enriched in zirconium or in uranium. The second phase of the RASPLAV Project started in July 1997 and concentrated on exploring the physical and chemical phenomena occurring in a convective molten pool. The effect of different corium compositions, the potential for and the effects of material stratification and the influence of various boundary conditions were investigated. The work involved a combination of integral and separate effect tests including molten-salt tests to investigate non-eutectic mixtures and the effects of stratification, extension of the material property database to allow interpretation and modelling of the experimental data. The CSNI decided to hold a seminar where the major outcome of the RASPLAV Project could be presented and discussed also in the context of other experienced activities on Severe Accidents. The objectives of the seminar are: - to review the experimental results of the RASPLAV Project; - to exchange information on complementary research; - to discuss the progress made on understanding severe accident progression; - to discuss the applicability to nuclear power plants and use of the results. The Seminar was intended to provide an in-depth review of the RASPLAV Project in terms of the technical capabilities, results and analyses produced during the project execution. The application of the results and their significance for power plant applications were addressed. Relevant results of the complementary research carried out at various laboratories were also presented. The seminar consisted of five sessions. The abstracts of the presentations are given in the appendix, as well as the list of participants and the conference program