Perspectives of Optimization of Technical Services and Maintenances Using Risk-Informed Decision-Making at NPPs in Ukraine

In most cases, when it goes about maintenance and repair optimization, the repair concept based on technical state of equipment is considered. This article describes the approach to maintenance and repair optimization at nuclear power plants by their transfer from the outage period to unit operation at power. The analysis of maintenance and repair optimization at foreign NPPs is carried out. The U.S. experience in reducing the outage duration is described. The article presents information on the pilot maintenance and repair optimization project at Zaporizhzhya NPP unit 2. The US Department of Energy through Argonne National Laboratory provides support in the implementation of the project in Ukraine focused on maintenance optimization of safety important systems based on risk-informed configuration management. The scope of this Project involves technical engineering analyses, plant personnel training, a study of improved economic performance indicators, and development of new strategies for NPP configuration, maintenance and operation. In order to optimize plant oeration, it is necessary to analyze plant commitments and requirements using effective, unbiased engineering assessments. Plant specific Probabilistic Risk Assessment combined with other engineering analyses techniques will be used for these assessments. This article also describes the results of the analysis of the preparedness of the Ukrainian regulatory framework for the implementation of the Project on maintenance optimization. The analysis focused on the U.S. and Ukrainian regulations and documents of the IAEA and WENRA international organizations related to maintenance optimization using riskinformed management of plant configuration. Based on the comparative analysis results, the authors identified possible limitations stipulated by non-compliance of the Ukrainian nuclear and radiation safety regulatory framework with the U.S. regulatory and methodological documents used for maintenance and repair optimization at the U.S. NPPs. In particular, the overview of USA regulations leads to the conclusion that they contain exhaustive requirements for the application of maintenance using risk-informed plant configuration management at all stages of its implementation, starting with the requirements for the alternative approach to maintenance and ending with the requirements for maintenance performance monitoring. Ukrainian regulations in turn contain only general provisions and areas for potential application of risk-informed approaches in operation and inspection. It should also be noted that the U.S. maintenance optimization methodology uses criteria based on the core damage frequency and large early release frequency. However, besides core damage frequency Ukraine uses the emergency release frequency criterion that does not correspond to the definition for large early release frequency used in the U.S.