Decrease to 50% of the rated power of Unit 6

Nuclear Facility: Unit 6, Kozloduy NPP
Date: 25.05.2021 Time: 11:30
Event title: Decrease to 50% of the rated power of Unit 6
Event description:
On 25.05.2021 Unit 6 operated at rated power. When routinely switching the oil pump of the control system of turbine driven feedwater pump No.2 (TDFWP*-2), the control valves of the drive turbine opened at 100 %. Despite the actions of the operators, the water flow increased and when it reached 4500 m3/h, TCP-2 tripped on “high water flow” protection signal. The technological protections unloaded the unit up to 48.9% according to the design algorithms. Activities have been undertaken to establish the reasons for switching off the TCP-2, as a result of which elements of the pump control system have been replaced. After a successful inspection of the control system, at 20:30 TDFWP-2 was switched on and the power increase was started in accordance with the requirements of the Technical Specifications for Safe Operation of Unit 6. There has been no violation of the operational limits and conditions and respectively there have not been any changes in the radiological conditions. * TDFWP supplies water to the steam generators and is part of the conventional (non-nuclear) part of the plant.
INES rating of the event: Below Scale/Level 0 No safety significance