The head of the International Atomic Energy Agency has inspected the disabled Fukushima Daiichi nuclear power plant. It is the first visit by Director General Rafael Grossi there since the plant's operator began releasing treated and diluted water into the ocean in August last year.

Grossi, who is visiting Japan, went to the nuclear plant on Wednesday.

He was accompanied by the president of the plant operator Tokyo Electric Power Company, Kobayakawa Tomoaki. The IAEA chief observed the equipment that checks treated water after being diluted with large quantities of seawater.

Kobayakawa explained about the usage of an undersea tunnel to release water about 1 kilometer off the coast. He also talked about a system for halting the release operation if a problem occurs.

Grossi later told reporters that the IAEA has been conducting its own independent sampling survey about the discharge. He said, "The results have been in line with what we were expecting."

He noted that the water release has a long way to go, but he described the operation so far as a "very encouraging start."

Grossi said that the IAEA will continue monitoring the operation.

Water used to cool molten fuel at the plant has been mixing with rain and groundwater. The accumulated water is being treated to remove most radioactive substances, but it still contains tritium.

Before releasing the treated water into the ocean, the plant's operator dilutes it to reduce the tritium levels to about one-seventh of the World Health Organization's guidance level for drinking water.

The IAEA reaffirmed in a report issued in January that the operation is consistent with international safety standards.