Grossi, on his 11th visit to the country since the war with Russia began, toured the Kyivska electricity substation.
Speaking to reporters alongside Ukraine's energy minister Herman Halushchenko and Energoatom's Petro Kotin, he said he wanted to assess the situation personally, saying the substation was very important to the functioning of the grid.
"Having external power supply is essential. A nuclear power plant produces power, electricity, but it also needs electricity in order to ensure its safety operation. When a power plant is not getting it - and it's through these kind of installations that it is getting it - it's like a blackout, so this compromises the safety of a power plant and it could eventually lead to an accident," he said.
Grossi added that it was clear that the "infrastructure has been degraded" but he had been "impressed with the work, the effort, being put in to ensure nuclear safety".
The IAEA has a team of experts stationed at the Zaporizhzhia nuclear power plant, which has been under Russian military control since early March 2022, and at Ukraine's three other operating nuclear power plants. He said they have also extended their inspections to nine substations that "are critical for the safe functioning of the nuclear power plants ... a nuclear accident can come with a direct attack on a nuclear power plant, but it can also be the result of disruption in the power grid".
Grossi is expected to have talks in Ukraine and in Russia during February as the IAEA continues its efforts to ensure the safety of nuclear power plants. The main focus remains on the six-unit Zaporizhzhia nuclear power plant, which is located by the frontline between Ukrainian and Russian troops.
The IAEA has set out basic rules to help ensure nuclear safety - namely that nuclear power plants should not be fired at, or fired from, and should not be used as a military base.
