In-Vessel Corium Formation and Relocation
EUROCOURSE 2003 CORIUM : Severe Accident R&D and Nuclear Power Plant Safety Janvier 27-31, 2003 Aix en Provence.
In-vessel corium formation and progression concerns the state of the reactor core from core uncovery up to reactor vessel meltthrough, or up to corium stabilization in accidents recovered. Corium formation and progression determines the in-vessel hydrogen generation, fission product behaviour, explosive and non-explosive molten fuel/coolant interaction and the coolability of the degraded core and the mode of vessel failure. It provides also important input for all reactor pressure vessel and containment failure issues. For example, the quantity, temperature, release rate and pressure of the corium released from the reactor pressure vessel and the amount of H2 and steam transferred to the containment can all have an effect on the integrity of the containment. This course focuses on the corium behaviour up to the transfer to the lower head. The experimental database available including small-scale, large-scale experiments and main TMI-2 core degradation results are described. Modelling aspects and severe accident codes are also presented. Complementary aspects related with in-vessel molten pools are briefly considered here but are described in more detail in course 9. Later phase related with coolability molten pools in lower head and vessel failure are described in course 9b. Finally, remaining safety relevant issues with identified uncertainties are summarized and perspectives are given regarding future European R&D efforts planned to reduce these uncertainties.