UN watchdog warns Ukraine war remains world’s biggest threat to nuclear safety

The war in Ukraine remains the most serious nuclear safety risk in the world as the conflict approaches its fifth year, the head of the UN’s nuclear watchdog warned on Friday. Ongoing fighting continues to threaten power supplies and critical infrastructure at nuclear sites located near combat zones, raising the risk of a serious accident.

Speaking to the Board of Governors of the International Atomic Energy Agency (IAEA), Director General Rafael Grossi said the agency’s top priority remains preventing a nuclear incident amid continued hostilities.

“The conflict in Ukraine is about to enter its fifth year,” Grossi said. “It continues to pose the world’s biggest threat to nuclear safety.”

IAEA teams remain deployed at all nuclear power plants affected by the conflict and issue regular assessments of safety and security conditions. The Board of Governors, the agency’s main decision-making body, brings together representatives from 35 countries to oversee nuclear safety, security, and safeguards. Its current members include Russia, the United States, the United Kingdom, and France.

Off-site power remains a critical lifeline

Grossi emphasized that reliable off-site power—electricity supplied from the national grid—is essential for nuclear safety. Without it, nuclear facilities must rely on backup systems to operate cooling and other vital safety functions.

“There must be secure off-site power supply from the grid for all nuclear sites,” he said, noting that this requirement forms the fourth pillar of the IAEA’s “Seven Pillars” framework for nuclear safety during armed conflict.

He also referred to Principle Three of the IAEA’s Five Principles for protecting the Zaporizhzhya Nuclear Power Plant (ZNPP), which states that every effort must be made to ensure off-site power remains available and secure at all times.

Grossi said both frameworks enjoy broad international backing, including from parties directly involved in the conflict, and that he has repeatedly urged compliance, including in briefings to the UN Security Council.

Limited progress at Zaporizhzhya amid persistent risks

Grossi reported recent progress at the Zaporizhzhya plant, Europe’s largest nuclear facility. On January 19, the plant was reconnected to its last remaining 330-kilovolt backup power line after repairs carried out during a temporary ceasefire coordinated with Ukrainian and Russian counterparts.

The line had been out of service since January 2, reportedly due to military activity.

Before the reconnection, ZNPP depended on a single 750-kilovolt main power line to supply electricity for critical safety systems, including cooling for its six shut-down reactors and spent fuel pools. IAEA experts are also monitoring winter-related risks at the site, such as preventing water in cooling and sprinkler ponds from freezing.

Power infrastructure beyond nuclear sites also at risk

Grossi stressed that nuclear safety in Ukraine depends not only on reactor sites themselves but also on the broader electrical grid.

“Damage to electrical substations undermines nuclear safety and must be avoided,” he said.

An IAEA expert mission is currently assessing ten key substations that are critical to nuclear safety, amid continued attacks on Ukraine’s energy infrastructure.

Other nuclear facilities affected

IAEA teams have also reported military activity near other nuclear installations, including the Chornobyl site. There, damage to a key substation disrupted multiple power lines and forced the temporary use of emergency diesel generators. The affected lines have since been restored.

Grossi said the IAEA’s presence has helped reduce risks and introduce a degree of predictability in an otherwise volatile conflict. However, he cautioned that technical safeguards can only go so far.

“The best way to ensure nuclear safety and security,” he said, “is to bring this conflict to an end.”