Krško Nuclear Power Plant start-up after successful repair of the damaged pipeline
Slovenian Nuclear Safety Administration (SNSA) has received a report from the Krško Nuclear Power Plant (NPP) on the event and the repair of the damaged pipeline as well as on the immediate and short-term actions taken to restart of the plant.
A part of the NPP's safety injection system pipeline, where a leak on the weld location was detected, has been replaced by 5 November. The part of the pipeline on the second branch of the safety injection system was also replaced as a precautionary measure, although no trace of leakage was found there. After the successful inspection of the installed materials and welds on the pipelines, the standard procedures for entering the criticality state and further restart of the plant were initiated.
The SNSA regularly supervised the execution of the repair work and was also informed on a daily basis of the planned activities for the repair of the pipeline during the unplanned outage, as well as the execution of the activities and inspection results. With the help of specialised technical support organisations, SNSA also carried out an assessment of the work performed.
Krško NPP submitted a report on the event and the repair of the damaged pipeline, as well as on the immediate and short-term measures taken to restart the plant. The short-term measures included non-destructive ultrasonic testing of the removed pipelines, functional testing of snubbers on the safety injection pipelines and installation of a temperature monitoring system on the safety injection pipelines. As part of the long-term measures, the NPP will carry out a detailed analysis of the cause of the leak. The two dismantled parts of the pipeline were sent abroad for destructive and metallographic examinations of the material and welds in a suitable hot cell laboratory. Based on the results of these analyses, the Krško NPP will take additional technical measures if necessary.
The replacement of both pipelines was a complicated procedure due to the radiation in the vicinity of the reactor vessel and the contamination of the pipelines. No worker received a radiation dose above the legal limits. The measured collective dose of all workers was lower than the dose estimated before the start of the repair work. The NPP personnel were well prepared for the repair work on the pipeline, all protective measures for the workers were taken, and effective decontamination of the work area and the pipelines was carried out.
The impact of the unplanned outage on the environment and the population was very low and comparable to the impact during normal operation of the NPP. Gaseous discharges to the environment were slightly increased during the unplanned outage, but the levels were still comparable to those during regular outages. All radioactive discharges were well below the legal limits set for the NPP.
The Krško NPP is expected to start supplying electricity to the grid in the coming days.