site.btaK-NPP Radiation Unchanged After Unit 6 Fault Report

Radiation conditions at the Kozloduy Nuclear Power Plant site were unchanged and were expected to remain so, the Nuclear Regulatory Agency said here on Friday, after information circulated about a fault in Unit 6’s secondary circuit.

The agency was notified of the case as part of its daily communication with Kozloduy NPP.

The activation of the devices was unrelated to the unit’s safety. There was no change and none was expected in radiation conditions at the Kozloduy NPP site, the agency added.

Unit 6 was reconnected to the power grid at 10:54 on December 16, 2025, after it had been taken offline as a precaution the previous day to replace a faulty protective device. It was then found that a protective diaphragm device on the turbine’s moisture separator reheater needed to be replaced; it is located in the unit’s conventional, non-nuclear part.

The annual overhaul of Kozloduy NPP’s Unit 6 ended on December 1, 2025. During the scheduled maintenance, which began on October 25, 2025, systems and equipment underwent preventive checks and technical servicing, along with all activities set out in the annual maintenance programme. The reactor was refuelled with fresh nuclear fuel for the 31st fuel cycle.

Kozloduy Nuclear Power Plant’s Unit 6 completed its annual maintenance on December 1, 2025, after being taken offline on October 25, 2025, and returned to the grid following an inspection and positive assessment by the Nuclear Regulatory Agency, the plant said. The overhaul included preventive checks and servicing, long-term operation measures, and refuelling for the unit’s 31st fuel campaign; output is increased in stages under technological requirements, while Unit 5 operates to schedule.

In the summer of 2025, Unit 6 was temporarily shut down for planned work linked to a coolant/heat-transfer-fluid leak in the third steam generator; the plant said monitoring remained well below regulatory limits and there was no change in radiation levels on site. Unit 6 was reconnected to the power grid on August 5, 2025, after repairs and testing.