Proposed general principles and safety requirements for CANDU nuclear power plants

A new set of safety requirements are proposed for licensing of CANDU nuclear power plants. These requirements combine present requirements, current practices and proposed modifications and may be considered as a development and an extension of the present approach in safety analysis. Six categories of events have been proposed, each one characterized by a consequence interval and by the maximum frequency of all events of consequences within the corresponding interval. For each category, maximum risk reference values can be derived which are equal or less than the risk derived from normal operation. An explicit cut-off frequency has been proposed beyond which there is no need to determine the consequences of an event. Single rare events and multiple coincident failures can now be treated on a more rational basis. Failures of subsystems are explicitly considered. Additional emphasis is put on safety support systems. A new criterion is proposed for analysing external events by which the risk of such events must not be significantly greater than would be experienced if no reactor were in the region. The proposed safety requirements, as well as the philosophy underlying these requirements, should improve the licensing procedure as well as the overall safety of a nuclear power plant. The proposed approach could also be used for safety evaluation of other industries. (auth)