Tokyo, Sep 29 (AP) The operator of Japan's wrecked Fukushima nuclear plant said Friday that much of the radioactive water stored at the plant isn't clean enough and needs further treatment if it is to be released into the ocean.

Tokyo Electric Power Co and the government had said that treatment of the water had removed all radioactive elements except tritium, which experts say is safe in small amounts.

They called it "tritium water," but it actually wasn't.

TEPCO said Friday that studies found the water still contains other elements, including radioactive iodine, cesium and strontium.

It said more than 80 per cent of the 900,000 tons of water stored in large, densely packed tanks contains radioactivity exceeding limits for release into the environment.

TEPCO general manager Junichi Matsumoto said radioactive elements remained, especially earlier in the crisis when plant workers had to deal with large amounts of contaminated water leaking from the wrecked reactors and could not afford time to stop the treatment machines to change filters frequently.

"We had to prioritise processing large amounts of water as quickly as possible to reduce the overall risk," Matsumoto said.

About 161,000 tons of the treated water has 10 to 100 times the limit for release into the environment, and another 65,200 tons has up to nearly 20,000 times the limit, TEPCO said.

Matsumoto said the plant will treat the water further to ensure contamination levels are reduced to allowable limits.

He was responding to growing public criticism and distrust about the status of the water.

More than 7 ½ years since a massive March 2011 earthquake and tsunami destroyed three reactors at the plant, Japan has yet to reach a consensus on what to do with the radioactive water.

Fishermen and residents oppose its release into the ocean. Nuclear experts have recommended the controlled release of the water into the Pacific as the only realistic option.

The release option faced harsh criticism at town meetings in Fukushima and Tokyo in late August, when TEPCO and government officials provided little explanation of the water contamination, which had been reported in local media days earlier.

TEPCO only says it has the capacity to store up to 1.37 million tons of water through 2020 and that it cannot stay at the plant forever.

Some experts say the water can be stored for decades, but others say the tanks take up too much space at the plant and could interfere with ongoing decommissioning work, which could take decades.(AP)

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