Ukraine's nuclear plants cut output after Russian strikes on substations

The cut followed a strike on 3 November, when Energy Minister Denys Shmyhal said Russia sent three drones towards a substation critical to the stable running of the Khmelnytskyi nuclear plant. The plant has two reactors and about 2,000 MW of capacity, according to IntelliNews. "Such actions pose a threat not only to Ukraine, but also to nuclear safety across Europe," Shmyhal said, Ukrainska Pravda reported. Ukraine alerted the International Atomic Energy Agency, he said.

The drone attack was part of a larger raid. EU Today, citing Ukrainian authorities, put the raid at 289 drones, 59 cruise missiles and 17 ballistic missiles aimed mainly at energy targets. Fakti.bg reported 310 drones for the same night. First Deputy Energy Minister Artem Nekrasov said the strikes had limited the system's ability to distribute what the plants produce. Emergency outages were in force in the Kharkiv region. Some consumers had no power in the Vinnytsia, Zhytomyr, Zaporizhzhia, Kirovohrad, Kharkiv and Kherson regions. The ministry said the capital region was worst off. Hourly outage schedules and capacity limits for industry applied in most regions, it said. DTEK said emergency outages can be imposed and lifted several times an hour because the grid state changes quickly after attacks.

Why substation damage cuts nuclear output

Substation damage can stop nuclear plants supplying the grid even when their reactors are not hit. Energoatom runs nine units with a combined 7,880 MW, about 44% of the 18 GW winter peak reached in January, Interfax-Ukraine reported in July. Nuclear carried 53-55% of Ukraine's generation in June, according to the Razumkov Centre. The 750kV substations that tie the reactors into the system use a voltage uncommon in Europe, where most transmission runs at 400kV or lower, which makes replacements hard to find and spare stocks thin.

The cut also protects the units. Nuclear plants supply baseload and cannot change output quickly, and a surplus on a damaged grid can trip a unit that then takes several days to restart, Oleksandr Vizir of the Ukraine Facility Platform warned in October. On 7 February, strikes on substations feeding the plants forced them all off the grid, leaving a shortfall of up to 8 GW, about half of consumption at the time. Ukrenergo chief Vitaliy Zaichenko later said that strike cut nuclear output by around 50% for a time. It is the nearest guide available to what is at stake, not a measure of the current cut.

What happens next

The Energy Ministry said output would return to normal only gradually. Crews are repairing the damaged networks. DTEK, the largest private energy company, said three of its thermal plants were fully taken out of operation on 3 November, removing part of the capacity that could otherwise cover for lost nuclear output.

Energoatom chief Pavlo Kovtoniuk said in July that the main task was to have every unit at full power by mid-November, before the heating season. The current cut lands inside that window. The ministry has not said when the plants will return to nominal output, and that depends on how fast crews can reach the damage and whether the next raid comes first.