Safety improvements in design and operation for CANDU nuclear power plants

Safety related design features embodied in CANDU nuclear power plants have evolved progressively since the construction of the first prototype unit in the 1950s. They have their origins in the lessons learned from the NRX research reactor accident in 1952. Canadian regulatory requirements together with operational policies and procedures have evolved in step with these improved design features. The paper discusses the basic directions which this evolutionary process is now taking or is expected to take over the next several years. Before proceeding with this discussion, the basic Canadian safety requirements are firstly summarized. This provides the reader with background regarding the basic requirements underlying these evolutionary directions. The first improvement area discussed is the increasingly comprehensive use of probabilistic analysis techniques as a powerful tool for the assessment of design adequacy and in providing plant operators with a more detailed insight into expected plant behaviour under possible upset and accident conditions. The paper then describes advanced digital computer applications in plant safety systems. These applications are being implemented in a progressive carefully planned manner to ensure that essential safety system reliability is not compromised. significant benefits are anticipated in improved operability and avoidance of spurious safety system actuation. The next section of the paper describes general improvements in the 'man-machine interface'. These are evolutionary in nature and build on the extensive experience gained in the application of on-line closed-loop computer control to CANDU reactors. A programme to reduce plant complexity is next discussed. The objective is to reverse past trends towards increasing complexity which have adversely affected plant operability. The final section briefly discusses the future role of safety related R and D programmes in the achievement of improved designs. (author). 2 tabs