Risk informed plant modifications and upgrades for life extension of Indian BWR

Probabilistic Safety Assessment techniques can be used to determine how ageing is affecting component and system unavailability; to identify plant components and systems that have a propensity to ageing and are risk significant. An essential requirement for PSA is the failure data for various components. An analysis of the failure data TAPS operation revealed that they were still in their useful life period. Hence, age related component modelling were not called for. With the objective of TAPS life extension, NPCIL initiated Level - 1 Probabilistic Safety Assessment (PSA) studies for Tarapur Atomic Power Station - 1 and 2. This Plant specific PSA Level - 1 study resulted in identifying and understanding the key plant vulnerabilities and in making recommendations for improvements by identifying risk significant systems and component and in particular, in case of TAPS, PSA has proved to be a valuable tool to understand the implications of non - conformance to the current standards and in making decisions on upgrades. The same methodology was used for trying out the different configurations of the system under consideration for upgrade and for optimizing the final decision on the same. These results are also useful for prioritizing the implementation of the upgrades/modifications, technical specification optimisation, where the maximum benefit for plant safety can be obtained. Insights available based on this risk informed study for TAPS life extension are discussed in this paper. (author)