Source terms for emergency planning in Ontario

Following a severe reactor accident, it is estimated that it would take about four hours to initiate an off-site response action. Decisions to implement such actions are based on predictions of the source term. During the first few hours, such predictions must be based on calculations, until reliable measurements can be obtained, and an emergency response is developed on this basis. The use of overly conservative assumptions, such as those used for licencing assessments, results in over predictions of the source term to such an extent that they may lead to inappropriate emergency responses, the risk of which may exceed the radiation risk. This paper discusses recent developments in the source term area and advocates the use of more realistic models and assumptions for source term predictions as input to emergency planning in the Province of Ontario