Groundwater at the crippled Fukushima No. 1 nuclear power plant site has passed detailed safety tests, officials said, and officials are preparing to vent hundreds of tons of water into the Pacific Ocean rather than store it as early as next Wednesday.
Tokyo Electric Power Co. is expected to spend the next few days completing preparations, including informing local communities.
Tepco carried out some of the radiation tests, but in a bid to ensure the results are seen as credible, other tests were conducted by the Japan Atomic Energy Agency and the Japan Chemical Analysis Center.
Beta ray-emitting isotopes such as strontium-90 were found to be undetectable, and cesium-134 and -137 were detected at below the safety threshold of 1 becquerel per liter.
Tepco said it will start releasing groundwater currently stored in one of the plant's tanks as soon as it has explained the findings to the Fukushima Prefectural Government and the Fukushima Prefectural Federation of Fisheries Co-operative Associations.
The first batch to be released will total around 560 tons of groundwater, said an official from the Ministry of Economy, Trade and Industry involved in the ongoing recovery effort. That amount of water will take about two hours to pour into the sea.
Tepco is under pressure to free up storage space after three years of filling up hundreds of hastily constructed short-term storage tanks.
Establishing a so-called groundwater bypass is considered a key measure to slow the buildup of highly radioactive water.
Local fishermen have agreed to the release of groundwater that meets stringent safety criteria.
Tepco is installing more tanks to ensure that it has reserve storage capacity, but it also wants to reduce the overall buildup of water requiring storage.