Utvärdering av förebyggande underhåll och åldringshantering av stationära blybatterier vid Forsmarks kärnkraftverk : Strategier, krav och förbättringar

Sammanfattning

The reliable performance of stationary lead acid batteries is essential for maintaining safety functions and defence in depth at the Forsmark Nuclear Power Plant, where the batteries supply auxiliary power during loss of offsite power (LOOP) events. As Forsmark prepares for operation up to 80 years, effective preventive maintenance and ageing management are critical to ensure continued system reliability. This thesis evaluates whether Forsmark’s current preventive maintenance programme for stationary lead acid batteries is adequate to ensure long term reliability or if improvements are required. The study analyses how well the programme addresses known degradation mechanisms such as temperature, charging conditions and ripple currents, and compares it with established industry practice, supplier recommendations and the ageing management principles defined in IAEA SSG-48. The work is divided into two parts. The first part reviews and evaluates Forsmark’s preventive maintenance documentation and benchmarks it against industry practice and the technical attributes for ageing management defined by the IAEA. The evaluation identifies gaps related to the lack of standardised capacity test interpretation, unsystematic temperature monitoring and limited use of trend analysis. Based on these findings, the second part develops an Excel and VBA based calculation tool that uses manufacturer plate performance diagrams to estimate capacity and time to a defined end of discharge voltage (1.80 V per cell) from partial discharge tests, enabling temperature corrected trend analysis. The development of this tool directly addresses the weaknesses identified in the first part, providing a practical method for predictive assessment and improved test evaluation. The results show that Forsmark’s programme is generally well structured and consistent with supplier guidance and international best practice but remains mainly condition based rather than predictive. The proposed calculation tool, together with systematic temperature monitoring and standardised test interpretation, strengthens the predictive capability of Forsmark’s ageing management programme and supports the long-term reliable operation of its safety critical battery systems. These measures are expected to enhance early detection of degradation and contribute to improved reliability assurance during Forsmark’s extended operation.