TOKYO, May 21 (Reuters) - The operator of Japan's destroyed Fukushima nuclear plant began releasing groundwater that it said is within legal radiation safety limits into the Pacific Ocean on Wednesday, in a bid to manage huge amounts of radioactive water built up at the site.
Tokyo Electric Power, or Tepco, has been fighting a daily battle against contaminated water since the Fukushima nuclear station was wrecked by a massive earthquake and tsunami in March 2011.
The controversial release, which was agreed by local fishermen after extended talks, coincides with a breakdown of a water treatment system for the highly contaminated water held in makeshift tanks.
It also comes amid revelations this week in the Asahi Shimbun newspaper that the majority of workers at the plant fled during the height of the meltdowns after the quake and tsunami knocked out cooling and backup power.
Groundwater flows down from nearby hills and 400 tonnes enters basements of the wrecked reactor buildings on a daily basis, according to Tepco's estimates, mixing with highly radioactive water used to cool reactors.
Workers then pump out the contaminated water, treat it and store it in more than 1,000 makeshift tanks that cover the facility grounds. The tanks that hold the most contaminated liquids are nearly full and workers are rushing to build more capacity.
Tepco said 560 tonnes of groundwater captured and stored before it entered the basements is to be released on Wednesday, using a bypass system that funnels it towards the sea after checking for radiation levels.
Using the bypass, Tepco hopes to divert on average 100 tonnes of untainted groundwater a day into the ocean.
A water treatment facility known as the Advanced Liquid Processing System, designed to remove the most dangerous nuclides, was completely shut down again this week. The system has not been fully operational since it was installed nearly two years ago.
The manager of the plant has admitted the repeated leaks and equipment malfunctions are "embarrassing."
About 90 percent of Tepco workers defied orders and left the Fukushima Daiichi plant on March 15, 2011, after an explosion rocked the site, the Asahi reported on Tuesday, citing unreleased transcripts of interviews with the manager at the time, Masao Yoshida.
Yoshida, widely viewed as a national hero for taking decisive action in the critical days and weeks of the disaster that prevented a more serious crisis, died of cancer last year.
Fukushima fishermen opposed plans to release groundwater for more than two years, fearing it would case even more damage to the reputation of produce from the region.
In March, local fisheries unions approved the plan, calling it a "painful decision," but necessary to stem the tide of radioactive water piling up at Fukushima. Many of them have been out of work after a voluntary ban on fishing in the area.
Tepco, the Japan Atomic Energy Agency and independent groups found that radioactive elements in the released water have less than 1 becquerels per litre of Cesium-134 and Cesium-137. All other radioactive elements checked are also far below standards for groundwater release.
The legal limit for releasing Cesium-134 into the ocean is 60 becquerels per litre. (Reporting by Mari Saito; Editing by Aaron Sheldrick and Simon Cameron-Moore)