KYIV, Ukraine — The head of the United Nations nuclear energy watchdog on Friday stepped up his calls for the creation of a safe zone around the Zaporizhzhia Nuclear Power Plant in Ukraine after renewed shelling caused a widespread blackout in the town where the plant’s workers live.
“This is an unsustainable situation and is becoming increasingly precarious,” Rafael Mariano Grossi, the director general of the International Atomic Energy Agency, said in a statement. “The power plant has no offsite power. And we have seen that once infrastructure is repaired, it is damaged once again.”
Mr. Grossi said that shelling had destroyed the power infrastructure feeding the plant’s satellite town, Enerhodar, leading to a blackout. There was “no running water, no power, no sewage,” he said.
“This is completely unacceptable,” he added. “It cannot stand.”
Ukrainian engineers at the plant are relying on its one active reactor to run the station’s critical safety and cooling systems — a precarious stopgap measure that reflects the desperation of the moment, Petro Kotin, the head of the Ukrainian national energy company, Energoatom, said on Thursday.
Mr. Kotin said in an interview on Thursday that while the emergency measure was known to the engineers and outlined in technical documents, it has never been tried for more than a few hours — and has already gone on for days.
The plant has been using the measure since it was disconnected from external power on Monday, leaving diesel generators as the last fail safe, a risky situation in a war zone where fuel supplies could be compromised.
Reconnecting to external power requires spare parts, Mr. Kotin said, and workers were racing to bring them from Ukrainian-controlled territory, crossing the front line to reach the Russian-controlled station. Even so, Mr. Kotin said the “degradation” of the facility continued to grow “worse and worse and worse.”
A team of inspectors from the I.A.E.A. visited the plant last week and called for the creation of a safe zone around the facility. Mr. Grossi has said for days that his biggest concern was the station’s ability to rely on external power.
While the reactors themselves are designed to withstand a plane crash, power is needed for essential cooling systems that are much more vulnerable. And since Monday, the plant has been running in what is referred to as island mode, using one “hot” reactor pumping out 140 megawatts of power — less than half its normal generation — to provide energy for essential plant equipment.
Mr. Kotin said that the reactor’s technical specifications do not envision this mode being used for more than an hour.
Edwin Lyman, a nuclear power expert at the Union of Concerned Scientists, a private group in Cambridge, Mass., said the situation was not unprecedented, but was also not standard practice. The I.A.E.A., which sets reactor safety standards for nuclear plants, published a technical document in 2018 that details the backup procedure, also known as “house load operation.”
Even plants that have the capability to run in island mode, the I.A.E.A. document noted, may face “a time limit, generally of a few hours.”
There are four high-voltage cables running from the plant to the Ukrainian grid and one lower-voltage backup line connected to a nearby fossil-fuel plant. But artillery fire around the plant — Ukraine and Russia each blame the other for the continued shelling — has severed those connections, plus two more lines that run to a small on-site power plant.
On Aug. 25, the plant was completely cut off from external power for the first time in its history, briefly plunging it into blackout and forcing the emergency diesel generators to be switched on. Engineers raced to repair the lower-voltage reserve line and reconnected the plant to the grid 14 hours later.
On Monday, that reserve line was severed again. Mr. Kotin said engineers made the difficult decision to keep one reactor running to supply power to the plant rather than switching immediately to the generators.
Ukrainian officials fear they could be forced to cycle down the plant’s last running reactor anyway, because it was not designed to work this way indefinitely.
