U.N. Monitor Aims to Cross Front Line in Ukraine to Inspect Nuclear Plant

The leader of the United Nations atomic watchdog said Tuesday that he would cross the front lines in Ukraine’s war against Russia to investigate conditions at the Zaporizhzhia Nuclear Power Plant, where the destruction of a nearby dam has compromised a key source of water to cool its reactors.

After meeting with President Volodymyr Zelensky of Ukraine in Kyiv on Tuesday afternoon, Rafael Mariano Grossi, the director of the International Atomic Energy Agency, said he was setting off on Tuesday evening to the plant in southern Ukraine that is occupied by Russian forces.

It was not clear what security arrangements had been reached with the warring sides but Mr. Grossi said he hoped to spend several hours assessing the situation at the plant, where inspectors from the I.A.E.A. are already stationed. Mr. Grossi and Ukrainian officials have said that there is no imminent threat of a meltdown, but his trip appeared calculated to call the world’s attention, again, to the precarious situation there.

An explosion a week ago at the Kakhovka hydroelectric dam on the lower Dnipro River unleashed a flood downstream and drained much of the reservoir that had served as the primary source of water for a cooling pond at the plant, which is critical to prevent a nuclear meltdown.

Mr. Grossi said that the loss of the water supply in itself is not a cause of “immediate danger,” but that any problem with the containment system for the pond on site could prove incredibly challenging. The pond provides water to cool the nuclear fuel inside the plant’s six reactors as well as spent nuclear fuel.

“If there was a break in the gates that contained this water or anything like this, you would really lose all your cooling capacity,” he said.

The pond is currently full and has a surface area of more than three square miles and a depth of more than 50 feet, according to Ukrainian officials. The water level is closely monitored and five of the nuclear plant’s six reactors are in cold shutdown mode, which greatly reduces the amount of water they require to ensure safety. A sixth still produces some steam, which is used for the plant’s internal operation, Mr. Grossi said.

Mr. Grossi has said in recent days that there is enough water in the pond to last for “several months,” but on Tuesday he painted a more pessimistic picture, telling journalists that “there could be water for a few weeks or maybe a month or two.” He said he was going to the plant to make a better assessment. The dam breach is “another step into the weakening of the safety net that one has in any nuclear power plant,” he added.

Mr. Zelensky said in a statement later that he supported an I.A.E.A. proposal to send its experts to assess the risk.

Europe’s largest nuclear power plant has faced a series of crises since Russian forces seized it more than a year ago amid a blaze of gunfire. Last summer, it was subject to repeated shelling and on at least one occasion artillery hit an area where spent nuclear fuel is stored.

Control of the plant, which is on the eastern bank of the Dnipro River, has given Moscow a degree of leverage over Ukraine’s energy production. It has not produced electricity for the grid since last year but even so it requires power from outside for safety purposes.

A single high-voltage cable has been bringing electricity in for much of the war. It has repeatedly been severed by shelling, leading to seven blackouts and the reliance on diesel generators, whose capacity can be measured in days, to keep safety systems running. On each occasion the external power has been quickly restored.

The risk that Ukraine faces at the nuclear plant stands apart, even amid the destruction of Russia’s full scale invasion, which has led to the occupation of parts of the country and the flight into exile as refugees of more than 8 million people. The United Nations says it has confirmed the deaths of about 9,000 civilians, but that it believes “the actual figures are considerably higher.”

It is the first time that a nuclear power plant has found itself in an active battle zone, according to Mr. Grossi, and concern over a potential accident is particularly acute in a country that experienced the worst civilian nuclear disaster in history, at the Chernobyl plant in 1986.

Mr. Grossi spent months trying to persuade the governments in Kyiv and Moscow to set up a security zone around the Zaporizhzhia plant, but was unable to secure agreement. In recent months, both sides have built up their forces along a front in the region east of the nuclear plant in preparation for a Ukrainian counteroffensive to reclaim land lost to Russia. The Ukrainian assault began in recent days and is expected to gather steam in the coming weeks.

More fighting in the vicinity of the plant would worsen instability, Mr. Grossi has said, but it is not the only risk. The British military intelligence agency has released satellite images showing that Russian troops have established shooting positions on rooftops in the plant and have brought in military equipment. Ukrainian authorities also say that Russia has stationed troops at the plant before they are deployed to the frontline.

In addition, Russia has for more than a year sought to impose management control at Zaporizhzhia, putting pressure on local workers to break their contracts with Ukraine’s nuclear energy company, Energoatom, and sign contracts with Rosatom, Russia’s own state nuclear firm.

The staff of 11,000 has been cut to a skeletal crew. Mr. Grossi confirmed Tuesday that many of the remaining workers are not allowed to go to the facility because they refuse to sign contracts with its Russian controllers. Workers who have escaped into territory controlled by Ukraine and some still at the plant describe an increasingly repressive environment. Some have accused the Russian occupation forces of detaining and torturing employees.

Nuclear experts say that the Russian actions violate a cardinal rule of civilian nuclear safety, which puts a premium on stable management control and a calm operating environment.

This was the backdrop when the dam was destroyed last week, draining the reservoir. Engineering experts say that a deliberate explosion inside the dam, which was controlled by Russian forces, probably caused its collapse.

In a measure of Kyiv’s distrust of Moscow, the head of Ukraine’s intelligence agency, the S.B.U. said Tuesday that Russian troops might attempt to destroy the nuclear plant just to forestall Ukraine’s counter offensive. He added, however, that it would be almost impossible to blow up the reactors.