An International Atomic Energy Agency (IAEA) mission will visit Japan next week to review plans to begin releasing more than a million tons of nuclear contaminated water from Japan's Fukushima Daiichi nuclear power plant into the sea, IAEA Director General Rafael Mariano Grossi said on Monday.

A team of about 15 experts will meet with government and utility officials during their February 14 to 18 mission, which includes a visit to the Fukushima Daiichi plant. The team is expected to include staff members from IAEA departments and laboratories, and an expert from each of 11 countries including South Korea and China, IAEA announced on its website.

The government and Tokyo Electric Power Company Holdings announced plans last year to begin gradually releasing the still-contaminated water in spring 2023 after further treatment and dilution. The plan has been fiercely opposed by fishermen, local residents and Japan's neighbors including South Korea and China.

Japan has sought IAEA's assistance to ensure the release meets international safety standards and gain the understanding of other countries. 

A massive earthquake and tsunami in 2011 destroyed the Fukushima plant's cooling systems, triggering the meltdown of three reactors and the release of large amounts of radiation, thereby causing the evacuation of over 160,000 people. Water used to cool the highly radioactive reactor cores has since leaked extensively, mixing with groundwater seeping into reactor buildings.

The water is being stored in about 1,000 tanks at the plant which need to be removed to allow for the wrecked plant's decades-long decommissioning. The tanks are expected to reach their capacity of 1.37 million tonnes later this year.

Japanese officials say the only realistic option is to slowly release the contaminated water, diluted with sea water, into the ocean. The discharge is expected to take decades to finish.

Officials say all isotopes selected for treatment can be reduced to low levels except for tritium, which is inseparable from the water but is harmless in small amounts.

The IAEA mission was originally scheduled for December but was delayed due to the global surge of the coronavirus variant Omicron. Japan's industry ministry and the IAEA have agreed to compile an interim report on the water discharge plan in 2022.

The IAEA review is conducted in an objective, credible and science-based manner and will help to send a transparent and credible message to the people of Japan and other countries, Grossi said. 

(With input from AP)