The water since used to cool the reactors is highly radioactive and mixes with groundwater in the underground levels of the reactor buildings.
Around 125 tonnes of contaminated water is transferred to vast tanks on the site every day, with Tokyo Electric Power Co (Tepco), the operator of the plant, estimating that storage capacity will be reached in the summer of 2022.
“The decision is clearly unacceptable – the Pacific Ocean must not be used as a dumping ground for nuclear waste,” said Shaun Burnie, senior nuclear specialist for Greenpeace.
“The Japanese government is choosing the cheapest option, not the best option, which is long-term storage,” he said.
The Japanese government has refused requests for independent testing of the water. The only official data on the contaminants are provided by Tepco.
“The contaminated water contains many radionuclides, which we know impact the environment and human health – including strontium-90,” said Mr Burnie.
Tepco initially claimed that the only significant contaminant in the water is tritium, which the company describes as “safe” because it is prevalent in daily life and does not build up in the body.
Documents provided to The Telegraph in 2018 by a source in the government show, however, that efforts to “cleanse” the water of radionuclides to “non-detect” levels have failed to eliminate radioactive elements, including iodine, ruthenium, rhodium, antimony, tellurium, cobalt and strontium.
Tepco subsequently admitted that levels of strontium-90 were more than 100 times above legally permitted levels in nearly 60,000 tons of water that had already been treated and were 20,000 times above safety levels set by the government.