Integrated assessment approach to ensure removal of decay heat with RCW out of service

In the unusual event that Recirculated Cooling Water System of a CANDU NPP is drained for maintenance or generally incapacitated and the reactor is in the Guaranteed Shutdown State, an alternative source of cooling water is required to remove decay heat. For the Cernavoda Unit 1 NPP, CNE-PROD assessed and proposed a novel arrangement to address this issue, prepared a design, and requested AECL to assess the proposed approach. As part of the assessment, AECL developed and performed an integrated approach that brought together a variety of design, operational, maintenance and safety considerations. First, a simplified hydraulic analysis was performed, the heat removal requirements of the system were reviewed and alternative heat sinks were evaluated. Then, the maintenance and operational implications were considered in detail, using AECL's Systematic Assessment of Maintenance (SAM) process. This included a detailed assessment of failure modes of interest and associated effects (Failure Modes and Effects Analysis). This assessment included consideration of the impact on operational chemistry. In addition, the safety implications (potential for human error and safety consequences of failure) were reviewed. Based upon the system requirements, hydraulic assessment, and maintenance review, several alternatives or improvements to the CNE-PROD proposal were developed. In addition, a number of operational suggestions, as well as additional concerns and considerations were identified. Finally, potential alternative solutions were looked at based upon previous AECL experience. This paper will describe the novel CNE-PROD arrangement and provide an overview of the integrated assessment approach taken by AECL (using Plant Life Management technologies) to evaluate the proposed arrangement and to identify additional considerations. (author)