Power was cut to Ukraine’s nuclear power plant at Zaporizhzhia on Wednesday for the second time in five days, the head of the United Nations’ nuclear watchdog said, a situation that leaves the plant relying on diesel generators for the fuel that it needs to cool its reactors.
Russian forces shelled an electricity substation in central Ukraine on Wednesday, knocking out power to the plant, the state energy company said. It was the latest in a series of Russian attacks on the country’s critical energy infrastructure in recent days.
Rafael Mariano Grossi, the director general of the United Nations’ nuclear watchdog, the International Atomic Energy Agency, said in a statement on Twitter that it was “a deeply worrying development” that underlined the urgent need for a safety and security zone around the plant, which is the largest in Europe.
On previous occasions, shellfire has damaged the power lines that bring electricity into the plant. But on Wednesday, rocket fire at a substation in the Dnipropetrovsk region farther north cut the power line to the nuclear facility, according to Energoatom, Ukraine’s state nuclear energy company. The substation is more than 100 miles from the nuclear facility.
The company said that it had tried to send fuel to Zaporizhzhia to replenish its stocks, but that as of 10 a.m. local time, Russian forces had prevented its vehicles from passing. It is not unusual for vehicles to be delayed when crossing a front line.
Although the nuclear plant’s backup generators switch on automatically, Energoatom said that cutting the electricity supply, which is needed to cool the reactors, risked causing a nuclear accident.
Shellfire at Zaporizhzhia last week caused a two-day power cut that ended on Sunday when the lines were repaired.
On Tuesday, Mr. Grossi met President Vladimir V. Putin of Russia in Moscow as part of efforts to prevent a nuclear accident at the plant, having also met President Volodymyr Zelensky of Ukraine last week.
Russian forces have controlled the plant since March, though it is still operated by Ukrainian workers and engineers. Last week, Moscow said that the plant would be brought within the Russian energy system. Such a move has been denounced by the Ukrainian authorities and the I.A.E.A.
