Risk-informed decision-making related to the on-line maintenance

Abstract On-line maintenance (OLM) represents the term, which includes testing and maintenance that is performed when the main generator of the nuclear power plant is connected to the grid. OLM on one side helps to decrease the number of activities, which would be performed during the scheduled outage, but on the other side it may contribute to a different level of risk, if the activity is performed when the plant is operating. If the risk of OLM during the power operation is much larger than the risk of similar activity performed during the shutdown the OLM may not be the desired strategy. Additionally, if the risk of OLM during the power operation is not larger than the risk of similar activity performed during the shutdown, the OLM would be the preferred strategy. The objective of the paper is to show risk evaluations of selected OLM activities of selected real plants and to examine if the current practices are suitable for the new nuclear power plants. The results of risk evaluations of OLM and their comparison show that the criteria or guidelines developed for existing plants are not completely suitable for new plants. The new power plants with expected lower risk measures, which can be lower for more than couple of orders of magnitude compared to existing plants, would be able to deal with OLM in plant configurations which would increase the risk for orders of magnitude, but would still be acceptable in terms of risk, if the existing criteria or guidelines are used. Results suggest that the risk guidelines for the OLM should be updated for their use in the case of new nuclear power plants.

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