Phenomena Threatening Containment Integrity and Evaluating Source Term Characteristics
Veikko Taivassalo, Eveliina Takasuo, Magnus Strandberg, Tero Tyrväinen, Ilkka Karanta, Anna Nieminen,
To assess phenomena threatening the BWR containment integrity more reliably, long-term debris bed coolability and possibility of hydrogen explosions to occur were analysed deterministically. When comparing VTT’s MEWA results on the debris bed post-dryout temperature to KTH’s DECOSIM results, a good agreement was achieved while the temperatures continued to increase, but the stabilized temperatures differed notably. Hydrogen explosions are possible in the containment only if the inertion is lost. This is most probable during the shutdown or start-up.
In addition, factors affecting source term characteristics, i.e. release temperature, altitude and probability were considered for different accident scenarios to further develop the methods and tools for PRA. Source term release height is usually the height of the location where the reactor building leaks or the height of the chimney if release is controlled. The temperature of release from containment is in most cases close to 100 oC but the temperature of radionuclides can potentially change during their migration in the reactor building.