Unit 6 of Bulgaria’s Kozloduy NPP is being taken offline for the replacement of a defective rupture disk on the turbine’s moisture separator reheater, located in the conventional (non-nuclear) part of the unit, according to the Kozloduy NPP website. No pollutants have been released into the environment, the NPP said.
The components of the device to be installed – the disk and the rupture pin – were manufactured from newly supplied materials equivalent to the original ones. Once the planned repair work is completed, unit 6 will be reconnected to the national grid. Unit 5, meanwhile is operating according to schedule. In December 2025, unit 6 taken offline twice due to a similar fault.
Ivaylo Mirchev is a prominent Bulgarian politician and businessman said the NPP has lost more than €55m ($65m) since 1 December 2025 due to stoppages and power reductions. Mirchev is a member of the National Assembly and a leading figure within the PP-DB (Prodlzhavame Promyanata – Demokratichcna Blgariya) a major pro-Western, liberal-conservative electoral coalition and the second-largest group in the Bulgarian Parliament. He complained that no explanations had been given for these incidents or measures to prevent future ones. He suggested that inferior material had been used in gross violation of regulatory documents.
However, this is a secondary concern compared with repeated forced shutdowns of unit 6 due to a leak in one of its steam generators. The problem involves cracks in the third steam generator. While the leaks often remain within safe regulatory limits, the unit is repeatedly taken offline as a “preventive measure” to perform repairs and ensure long-term stability. Repeated cracks have been detected in a specific section of the generator’s heat exchange tubes. An investigation is currently underway to determine the “root cause” of the cracks. This caused multiple shutdowns, including significant outages in June 2024, July 2025, and December 2025.
