Zaporizhia NPP loses power connection during increased military activity

28 November 2023

The Zaporizhia NPP (ZNPP) lost the connection to its main off-site power line, forcing it to rely on back-up electricity for reactor cooling International Atomic Energy Agency (IAEA) Director General Rafael Mariano Grossi said in his latest update. IAEA experts present at the ZNPP heard several rockets that appeared to have been fired from close to the plant. The IAEA team did not see the projectiles because of clouds but the distinctive sound indicated they were fired from a Multiple Launch Rocket System (MLRS) nearby.

“Today’s events once again clearly demonstrate the extremely fragile nuclear safety and security situation at the Zaporizhia NPP,” said Grossi. “The plant – located on the frontline – continues to face many potential threats as a result of this tragic war,” he added. “I remain deeply concerned about nuclear safety and security at the plant, both when it comes to its vulnerable off-site power supplies – which can be affected by attacks far away from the site – and the more direct military risks it is facing, potentially undermining the principles that I set out at the United Nations Security Council in May. In this context, the apparent firing of rockets from near the plant is a special source of concern,” he said.

Russia took control of ZNPP in March 2022 as part of its special military operation in Ukraine. In October 2022, Russian President Vladimir Putin signed a decree formally transferring ZNPP to Russian jurisdiction under nuclear utility Rosenergoatom (part of Rosatom). A Russian Federal State Unitary Enterprise. Zaporizhia NPP was established by Rosenergoatom to operate the plant. However, Ukrainian nuclear utility Energoatom still claims ownership of the plant.

The ZNPP said a short circuit that occurred around 100 kilometres north of the plant caused the cut in the connection to its sole remaining 750 kilovolt (kV) power line – out of the four that existed before the conflict. The plant continues to receive external power from its only available 330 kV back-up power line. However, one emergency diesel generator also started operating to supply reactor unit 4 after the power loss, indicating a possible issue with its electrical configuration. The diesel generator was manually shut down after ten minutes. Unit 4 is the only reactor of the six on the site that is in hot shutdown in order to continue providing power and heat for essential safety operations at the plant. The other units are all in cold shutdown.

The plant said the 750 kV line is being repaired but it was not clear when it will be reconnected. ZNPP has lost external power supplies repeatedly during the conflict, including seven complete loss of off-site power events. On each of those occasions, the operation of emergency diesel generators at the site was required to provide the electricity needed by the plant for vital nuclear safety and security functions, including reactor cooling. The connection to the 750 kV line was last lost on 10 August.

The previous day, IAEA experts said they had observed an emergency exercise conducted at ZNPP. The exercise focused on actions that should be taken in response to a hypothetical break of a pipe containing radioactive wastewater and the disconnection of power from one reactor unit.

The IAEA experts followed the two-hour exercise from the ZNPP’s temporary emergency centre, observing the coordination of emergency response actions. They also observed field activities during the exercise, including radiation and contamination monitoring as well as preparations for the evacuation of some plant staff. After the exercise was completed, the IAEA team observed the standard debriefing. Overall, the IAEA experts said the exercise scenario was carried out as planned.

“Having effective emergency preparedness and response arrangements is one of the seven indispensable pillars for ensuring nuclear safety and security in an armed conflict. It is vital that the Zaporizhia Nuclear Power Plant tests its emergency response arrangements. We encourage the plants in Ukraine to conduct more exercises in future to further test their emergency preparedness,” Grossi said.

Earlier ZNPP’s unit 5 had reached cold shutdown, leaving only unit 4in hot shutdown to produce steam and heating. The plant decided to move the unit from hot shutdown after boron was detected in a secondary cooling circuit, albeit at levels below the limits set by its technical specifications. No radioactivity has been detected in the secondary cooling circuit. Borated water is used in the primary coolant to help maintain nuclear safety functions.

After the cold shutdown state was reached at unit 5, ZNPP informed the IAEA team that it will not immediately investigate the cause of the presence of boron in the secondary cooling circuit of one of the unit’s steam generators. The IAEA experts will continue to monitor this issue during its discussions with ZNPP and walkdowns of the plant.

The IAEA experts are also continuing to gather information to fully understand why unit 6 temporarily lost power on 14 November and relied on a diesel generator for 90 minutes. They held multiple discussions on this issue with the ZNPP’s electrical department.

Unit 4 continues to provide steam for nuclear safety related activities at the ZNPP and also for heating at the site and the nearby town of Energodar, where most plant staff live. Additional heating is provided by mobile diesel boilers installed at the ZNPP together with boilers located in the nearby industrial zone.

Image: Zaporizhia nuclear power plant (courtesy of IAEA)

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