Severe accident mitigating measures in the Ringhals and Forsmark plants and resulting reduction of the source term

In the paper the severe accident mitigating measures in the Ringhals and Forsmark plants are outlined. A strong emphasis is put on both hardware and procedural measures to ensure that the reactor is brought back to a stable cooling state and that the containment integrity will not be endangered. Specific measures to protect the BWRs in the early stage of an accident sequence will be implemented such as protection of penetrations from molten core debris and the possibility to vent the containment in the case of a loss of coolant accident combined with the loss of pressure suppression function. An important part of the envisaged strategy after vessel melt-through is to supply water to the containment as soon as possible to avoid pressure build-up, to wash out aerosols and to reach a final stable state by covering the remaining core with water. In the case of a late pressure build-up a filtered vent will limit the release of radioactive products to less than 0.1% of the core inventory of Cs and I in a 1800 MWt reactor according to the requirements by the Swedish government. The analysis performed so far has shown that this limit is met with a wide margin. (author). 2 refs, 3 figs