Ukraine plant loses only remaining backup power line

This is the latest in a series of incidents highlighting ongoing nuclear safety and security risks more than two years into the conflict between Russia and Ukraine, said IAEA director general Rafael Mariano Grossi.

IAEA experts stationed at the plant reported that the sole remaining 330-kilovolt line was disconnected at 10:06 a.m. local time on April 4, leaving the plant entirely dependent on its sole remaining 750-kV line for off-site power. Prior to the start of the conflict in February 2022, Zaporizhzhia had four 750-kV and six 330-kV power lines available.

The cause of the latest outage was not immediately clear, but it followed reports of military activity in the region. The IAEA team on the ground reported hearing the firing of rockets on April 3 and numerous rounds of outgoing artillery fire on April 4. Staff at the site reported hearing daily explosions for the past week at various distances from the plant.

Quotable: “As has happened repeatedly during this devastating war, Europe’s largest nuclear power plant has lost a key source of the electricity it needs to cool its reactors as well as for other essential nuclear safety and security functions. This morning’s developments once again underline the very real dangers facing this major facility,” Grossi said.

Background: Zaporizhzhia has been under Russian military control since March 2022. It is one of the 10 largest nuclear plants in the world and is Europe’s largest.

The plant stopped producing electricity for the national grid in September 2022, but it has kept at least one of its six units in hot shutdown to provide district heating as well as process steam for liquid waste treatment at the site. Earlier this year, the plant started operating four newly installed diesel steam generators to handle such waste. Unit 4 has remained in hot shutdown primarily to provide heat to the nearby town of Enerhodar, where most of the plant staff live. The five other reactors are in cold shutdown.

Since August 2022, Zaporizhzhia has suffered eight events with a complete loss of off-site power, most recently in December 2023. The 330-kV line was also disconnected for three weeks earlier this year, but the main 750-kV line remained available at that time.

What’s next: The IAEA team at Zaporizhzhia discussed last week putting Unit 4 into cold shutdown, now that the winter heating season for Enerhodar is over. According to Grossi, the move to cold shutdown would be “more favorable for nuclear safety and security, but it should not detract from the fact that the situation at the Zaporizhzhia nuclear power plant remains highly precarious.”

The IAEA team continues to perform walkdowns at the site, including to some of the reactor units as well as to the plant’s inlet and discharge channels, where they can also observe the cooling towers and their pumping station. The water supplied from the site’s eleven underground wells is providing enough cooling water for the six units in shutdown, the team has reported, but it is still not enough to maintain the water inventory in the plant’s cooling pond.

The Russians controlling the plant have not given the IAEA access to all parts of the plant. Last week, the agency's team was denied access to the cooling pond isolation gate, a location last inspected by the team in November 2023.

During a recent visit to the Unit 4 reactor building, the IAEA observed the chemical analysis laboratory and the safety system rooms. No leaks or traces of boric acid were seen, but the team noted what appeared to be some crystallized boric acid in one of the sump intakes during a visit to the Unit 1 sumps for the emergency core cooling system. Borated water is used in the primary coolant to help maintain nuclear safety functions. Although leaks may occur, prompt investigation, repair, and cleanup are crucial to prevent potential damage to any system important to nuclear safety.

Elsewhere in Ukraine: The State Nuclear Regulatory Inspectorate of Ukraine informed the IAEA that a research and development facility in the country’s northeast—used before the war to produce radioisotopes for medical and industrial applications—also lost off-site power due to shelling. The facility now relies on emergency diesel generators, as it did during a previous weeklong outage at the end of March. The on-site radiation situation is within normal limits, the inspector said.

Also, the subcritical Neutron Source installation, located in the Kharkiv Institute of Physics and Technology in eastern Ukraine, was transferred to a deep subcritical state at the start of the war, and its radioactive inventory is low. In November 2022, an IAEA safeguards and nuclear security expert mission found that the facility had been heavily damaged by shelling, but there was no indication of radiological release or diversion of declared nuclear material.

“As this facility has been shut down since the start of the armed conflict more than two years ago, we do not currently expect the situation to have any consequences for public safety. But it also underlines the potential risks to nuclear safety and nuclear security during the military conflict and we will continue to monitor the situation at the facility,” Grossi said.

The IAEA teams at Khmelnytskyi, Rivne, and South Ukraine nuclear power plants, as well as at the Chernobyl site, reported that nuclear safety and security continues to be maintained despite multiple air raid alarms over the recent past. Maintenance in the Unit 2 turbine hall at Khmelnytskyi has been completed, and the reactor has returned to nominal power. Unit 4 at Rivne remains in planned outage.