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Late phase source term phenomena


The aim of the LPP project is to quantify fission product and core materials released from molten corium. This work has examined the kinetics of release of the key fission products, lanthanides and actinides (as simulants), and also allowed the importance of key phenomena (e.g. sparging, slag formation, two-phase systems) to be examined. A series of experiments to aid with understanding the chemistry of species released during the late phase of an accident has also been carried out, together with experiments aimed at examining the long-term behaviour of a solidified core immersed in a water pool. The results from these experiments have been used to test and develop code models for the relevant phenomena. The models and experimental results have also been considered in plant calculations for Eastern European and advanced reactor designs. The results of the project will aid in the development of severe accident management strategies and provide data on fission product behaviour in the late phase of an accident. Such data are also important in the interpretation of results from the Phebus FP programme. The objectives of the project were as follows: - To provide an experimental database on the kinetics of release of fission products and core materials released from molten pools, with emphasis on sparging, slag formation, two-phase pools, the oxygen potential of the atmosphere and melt composition. - To conduct experiments on the release behaviour of lanthanides and actinides simulants. - To provide data on the identity and physico-chemical form of fission products released in the late phase of an accident. - To provide experimental data on the long-term behaviour of fission products leached from a solidified core immersed in a water pool, with consideration of the entrainment of leached fission products. - To conduct experimental assessments, model development and code testing using experimental data. - To conduct sensitivity studies to address long-term coolability and impacts on radiological source term in the context of plant calculations for existing and future reactors. Experiments were conducted to study the processes affecting fission product and core materials released from molten pools. These studied the effects of temperature, oxygen potential, sparging, slag formation, two-phase pools and melt composition on the release. The behaviour of simulant lanthanides and actinides was also studied. In addition to the parameters for the metallic melt experiments, releases from oxide pool and crust effects were studied in the ceramic melt tests. Experiments were conducted on the transport and aerosol behaviour of ruthenium released in the late-phase. These studies examined the species formed under accident conditions. In addition, experiments were conducted on the leaching behaviour of solidified core debris. This was immersed in water at ~100°C for different periods of time. An assessment of the experimental conditions was made, in order that they were as representative as possible. The experimental and modelling studies were integrated with plant assessments. These examined the consequences of an accident in terms of the plant behaviour (radiological source term and coolability of the molten pool). These will aid with the development of severe accident management strategies (e.g. immersed core). Operational Eastern European plants, and advanced reactors were studied.