CSNI Workshop MASCA Seminar 2004 Hosted by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) Aix-en-Provence, France 10-11 June 2004 The NEA has, since 1994, sponsored collaborative projects on severe accidents carried out at the RRC KI in Russia. These projects, entitled the RASPLAV and the MASCA Projects, consisted of a programme of experiments and analyses intended to address the conditions under which molten core material can be retained inside the reactor pressure vessel (RPV) by cooling of the vessel from outside. The results have been of wider applicability in that they have provided new insights as to the behaviour of molten corium pools and consequent heat load on the lower head of the reactor pressure vessel. These results are important since the thermal conditions affect the lower head failure mode (and the consequent pouring and spreading of the melt). The RASPLAV Project demonstrated that the corium melt behaved comparably to the simulant material in its natural circulation, therefore previous evaluations based on simulant material data could be scaled to prototypic reactor conditions. However, two of the four RASPLAV tests exhibited an unexpected behaviour. Sufficient knowledge of fission product spatial and chemical distributions in the melt pool is lacking. Well-designed experiments obtained with corium compositions prototypical of power reactors was supposed to provide the technical support for assessments of the in-vessel melt pool retention strategy as well as of ex-vessel phenomena. The MASCA tests covered this accident management need. This goal was achieved through corium tests of different scale, including pre- and post-test analyses and development of computational models. Additional measurements of thermo-physical properties of the melts such as density, thermal conductivity and liquidus-solidus temperatures considerably expanded the material properties database obtained in the RASPLAV Project. The objectives of the MAterial SCAling (MASCA) project were to: investigate the influence of chemical behavior on heat transfer in stratified molten pools (U-Zr-O-Fe(SS)-C(B)); investigate FP behaviour in a molten pool and in particular partitioning of FP between layers in case of stratification; partitioning of FP between phases during melting and solidification; distribution of FP simulants in the melts; expand material properties data base; develop computer models describing relevant phenomena. The CSNI decided to hold a seminar where the major outcome of the MASCA Project could be presented and discussed also in the context of other experienced activities on severe accidents. The objectives of the seminar were to: review the experimental results of the MASCA project; exchange information on complementary research; discuss the progress made on the understanding of severe accident progression; discuss the applicability to nuclear power plants and use of the results. Related links Seminar programme NEA Committee on the Safety of Nuclear Installations (CSNI) RASPLAV project MASCA project Institut de Radioprotection et de Sûreté Nucléaire (IRSN) Organising committee (restricted access) © 2004 Organisation for Economic Co-operation and Development Last updated: 26 March 2004