Research and Development Activities in Level-1 Probabilistic Safety Assessment and Aging Studies

Research and development activities that are in progress in Reactor Safety Division in the areas namely Level-1 Probabilistic Safety Assessment (PSA) and ageing of control and instrumentation components and cables are presented. The results of AHWR level-1 PSA studies carried out are presented. PSA studies have applications in many areas. A software “Risk Monitor” was developed that can be used to continuously monitor the status of the Nuclear Power Plant (NPP) with regard to the functioning or non-functioning of its different subsystems and assess the associated risk emanating from the facility on the basis of this information. Probabilistic precursor analysis studies have been initiated for assessing risk arising out of the events that occurred during the operation of the plant. A case study has been carried out for a typical NPP. All the PSA studies are dependent on failure parameters that enter into various component models. A case study has been carried out, along with NPCIL and AERB for assessing more applicable failure parameters for class IV failure frequencies using Bayesian methods. Fire PSA studies have been carried out for MAPS, as a case study, to identify the vulnerable areas. Pilot studies on Risk informed In-Service-Inspection studies have been carried out, for a typical NPP and a section of Heavy Water Plant, for categorizing the components for In-Service inspection based on their contribution to risk. These two pilot studies indicate that RI-ISI has a very high potential in reducing inspection requirements compared to the requirements as per the currently adopted standards. A neural network based diagnostic system for identification of accident scenarios in 220 MWe Indian pressurized heavy water reactors (PHWRs) has been developed for operator support and accident management. Various facilities have been set up and a few were updated for carrying out the Thermal & Radiation Ageing and Loss Of Coolant Accident (LOCA) Qualification Studies of Control & Instrumentation (C&I) components and Equipments. Instrumentation systems for carrying out these studies are also being up dated. Nowa-days digital systems are increasingly being used in instrumentation and control. Studies based on physics of failure are in progress to address the issues related to their failure, which are needed in PSA studies. Even though software that goes into these systems undergoes extensive validation and verification, quantification of the failure rates of these software are needed in PSA studies. Work on software reliability is also under way.