Application of PSA based operational event analysis to Indian nuclear power plants

In the aftermath of catastrophes, it is common to find prior indicators, missed signals and missed alerts that if recognized and appropriately managed well in time, the undesirable events can be averted. It has lead to the practice of identifying such indicators, also known as precursors, and carrying out accident sequence precursor analyses. The results of such analyses help significantly in design evaluation, precursor management and risk assessment. In AERB, the practice has been started of analyzing significant precursors in the Nuclear Power Plants (NPPs). Spurious opening of Instrumented relief valves (IRVs) are observed in Indian NPPs. A similar incident occurred in one of the NPP unit recently. The incident also involved the light water injection through Emergency core cooling system (ECCS). The event is analyzed both deterministically and probabilistically for assessing the safety significance of the event, identification of possible precursors. The operating event has also provided an opportunity to validate the assumptions and models used in the Probabilistic Safety Assessment (PSA) carried out for the plant.