NHK has learned that the head of the International Atomic Energy Agency is making arrangements to visit Japan early next month, before treated and diluted water from the crippled Fukushima Daiichi nuclear power plant is released into the ocean.

Water used to cool molten fuel at the facility mixes with rain and groundwater. The water that accumulates is treated to remove most radioactive materials, but it still contains some tritium.

Japan's government plans to dilute the filtered water to bring the concentration of tritium well below the percentage permitted by national regulations.

The amount of tritium in the diluted water is also expected to be below the World Health Organization's guidance levels for drinking water quality.

The government wants to start releasing the treated and diluted water around the summer of this year.

At the request of the Japanese government, the IAEA sent a team of experts to Japan. The experts assessed the safety of the plan from February of last year through this month. A comprehensive evaluation report is due out shortly.

Government officials say IAEA Director General Rafael Grossi is planning to personally hand the report to Japanese Prime Minister Kishida Fumio.

Kishida is expected to make a decision about the timing of the release, after he meets with Grossi and studies the report.