Controversial plan that is crucial part of crippled plant’s decommissioning will be monitored by UN nuclear watchdog.
Plant operator Tokyo Electric Power Company (Tepco) said on Thursday that weather and sea conditions were suitable and that it would switch on the seawater transfer pumps at around 1pm (04:00 GMT) to begin the discharge into the Pacific.
More than one million metric tonnes of the treated water, used to cool the wrecked reactors after the 2011 tsunami, is currently stored in some 1,000 tanks around the site and its removal is a key part of decommissioning the still highly dangerous facility.
Monitors from the International Atomic Energy Agency (IAEA), which has backed the plan, will be on-site for the discharge, and samples of water and fish will be taken.
Japan says all radioactive elements have been filtered out except tritium, which is hard to remove from water. The hydrogen isotope is also discharged – at higher levels – by operational nuclear power plants, including in China and France.
The company will carry out four releases of treated water until March 2024, with 7,800 cubic metres of water released each time. The first discharge will take about 17 days.
That water will contain about 190 becquerels of tritium per litre, below the World Health Organization drinking water limit of 10,000 becquerels per litre, according to Tepco. A becquerel is a measure of radioactivity.
‘Extremely selfish’
The plan has sparked continuing controversy despite Japan’s insistence that the process is safe and the backing of the IAEA, the United Nations’s nuclear watchdog, which approved the proposal in July, saying the impact on health and the environment would be “negligible”.
On Wednesday, China said it would take necessary measures to protect the marine environment, food safety and public health.
Foreign ministry spokesperson Wang Wenbin called Japan’s move “extremely selfish” and said China had lodged a formal complaint over the decision.
China and the territories of Macau and Hong Kong have also banned Japanese seafood imports from around Fukushima and Tokyo, and stepped up radiation monitoring. Hong Kong Chief Executive John Lee called the discharge “irresponsible”.
South Korea has also been cautious amid public concern, despite a government assessment finding no problems with the scientific and technical aspects of the release.
On Wednesday night, South Korea’s main opposition party led a candlelit vigil against the discharge.
The Fukushima Daiichi plant was devastated in March 2011 after it was overrun by a tsunami triggered by a 9.0 magnitude earthquake that killed nearly 20,000 people in northeastern Japan.
It was the world’s worst nuclear disaster since Chernobyl in 1986.