The government and Tokyo Electric Power Co. are considering pumping up contaminated groundwater from 42 wells around the Fukushima No. 1 nuclear power plant's Nos. 1 to 4 reactors and releasing it into the Pacific Ocean after removing almost all radioactive substances, The Yomiuri Shimbun has learned.
The plan is aimed at curbing an increase in contaminated water in reactor and turbine buildings by reducing the amount of groundwater flowing in.
TEPCO expects to be able to reduce the amount seeping into the buildings, currently about 300 to 400 tons a day, by about 200 tons.
Along with frozen-soil walls, it will be a key measure for dealing with contaminated water at the plant, according to TEPCO.
Aiming to start the release of the groundwater into the sea in autumn, TEPCO plans to provide an explanation to local fisheries cooperatives later this month.
Known as subdrain pits, the wells from which the groundwater will be pumped surround the reactor and turbine buildings.
Before the nuclear crisis began in March 2011, TEPCO was already pumping groundwater from 57 subdrain pits at the plant and releasing it into the sea because it flowed into the buildings when water levels grew too high.
However, it became impossible to use the subdrain pits, partly because the pumps were damaged in the Great East Japan Earthquake in March 2011.
In addition to 27 repairable subdrain pits, TEPCO is constructing 15 new wells, planning to pump up contaminated groundwater from a total of 42 subdrain pits and release it into the harbour of the crippled plant.
Groundwater to be pumped from the subdrain pits is contaminated with radioactive substances released into the air from the plant at the time of the nuclear crisis. TEPCO will build water purification equipment by this autumn to remove most radioactive substances, such as cesium, from the tainted water.
The Nuclear Regulation Authority is currently examining the safety of the water purification equipment.
As a similar measure to deal with contaminated water, a so-called groundwater bypassing operation has been carried out using wells near mountains.
In the operation, pumped groundwater is temporarily kept in tanks to analyse the water quality and released into the sea once radiation levels are confirmed to be lower than the standards set by TEPCO and the government.
In the measure involving the subdrain pits, similar steps are expected to be taken.
Groundwater to be pumped up from some of the subdrain pits includes high levels of tritium, a radioactive substance that cannot be removed with the purification equipment.
However, TEPCO believes it is possible to lower the total level of radioactive substances to levels that meet standards if the water is mixed in tanks with water pumped from other subdrain pits.
In July, the government and TEPCO provided the Fukushima Prefectural Federation of Fisheries Cooperative Associations with an explanation of the draft layouts of pumping systems and other equipment for the release of tainted water into the sea.
They hope to obtain the understanding of local fishermen by holding explanatory meetings for individual fisheries cooperatives affiliated with the federation in August.