The relationship between reliability and safety in nuclear power plants

This paper is concerned primarily with the problem of taking account of the relationship between reliability and safety at the conceptual design stage. The relationship between availability and safety is discussed and a composite set of quantitative criteria, in a form suitable for use in the design stage, is derived. This set has been used as a basis for the studies employed for illustrative purposes in this paper. A method is described by which reliability engineering techniques can be applied to reactor design at the conceptual stage in order to clarify the more important safety aspects. By the use of this method it is possible to determine the reliability which will be required from each of the major protection systems (i.e. reactor shutdown, core cooling and containment) and from certain critical structures in order that the reactor should meet a given set of safety criteria, specified in quantitative terms. The application of this method to the case of an SGHWR is described. Possible ways of reducing the reliability required from the reactor protection systems are discussed. (author)