The Japanese government and Tokyo Electric Power Company (Tepco) plan to release treated radioactive water from the Fukushima Daiichi NPP about 1 kilometre off the coast, according to a plan released by Tepco on 25 August. The treated water, containing radioactive tritium, will be released through an undersea tunnel. The government and Tepco concluded that the use of such a tunnel would create less reputational damage than releasing the water directly from the coast near the plant.
Tepco is expected to conduct a drilling survey for geological research in September or later as the undersea tunnel needs to penetrate bedrock. It will submit the construction plan to the Nuclear Regulation Authority (NRA) by the end of September, aiming to build the tunnel by the planned start of the water release around spring 2023. The tunnel will stretch 1 km east from the plant out to sea, releasing the water into an area of the ocean where no fishing rights are in place.
More than 1 million tons of treated water has accumulated at the Fukushima NPP since the March 2011 earthquake and tsunami triggered the meltdown of three reactor cores. Water pumped into the ruined reactors at the Fukushima plant to cool the melted fuel, mixed with rain and groundwater, which has also been contaminated, is being treated using an advanced liquid processing system (ALPS). The process removes 62 radionuclides, including strontium and caesium, as well as Carbon-14, but leaves behind tritium.
While the level of radioactive tritium that remains in the treated water will be diluted to below regulatory standards, the decision to release it offshore into the Pacific is aimed at preventing reputational damage to local marine products amid an outcry from fishermen.
According to an official in charge of the water discharge project, Junichi Matsumoto, who works for Tepco’s Fukushima Daiichi Decontamination & Decommissioning Engineering Co, said the undersea tunnel will be constructed by hollowing out bedrock on the seabed near the unit 5 reactor at the Fukushima plant and the water will be released at a depth of about 12 metres below the ocean's surface. The controlled release, with an annual cap on radioactive materials, will continue for about 30 years, or until the plant's decommissioning ends, Matsumoto said.
Tepco plans to dilute the treated water with a large amount of seawater to reduce its tritium concentration to less than 1,500 becquerels per litre. As the seawater within the nuclear plant’s port area contains radioactive materials, the water will be taken from outside the port.
The Japanese government said it will buy marine products as an emergency step to support fishermen if the planned discharge of treated water from the Fukushima plant into the sea hurts their sales. The government on 24 August adopted an interim plan that includes a fund to cushion the impact of any negative reports about the discharge and compensate fisheries and other local businesses for any damage.
Tepco had also considered directly releasing water from within the plant site to reduce construction work, but the diffusion of tritium remained a key concern. It said it will increase the sampling locations and frequency of tritium concentration measurements in the surrounding area.
Japanese officials have said the ocean release is the most realistic option for disposing the water, which they say is required for the decommissioning of the plant. Government and Tepco officials say tritium, which is not harmful in small amounts, cannot be removed from the water, but all other isotopes selected for treatment can be reduced to safe levels before release.
Tepco said in a press release introducing its plan that it “would like to sincerely apologise for the great burden and inconvenience that the Tepco Fukushima Daiichi Nuclear Power Station Accident has caused on the people of Fukushima, and society as a whole”. Tepco said it was presenting its response regarding the handling of ALPS treated water at Fukushima Daiichi while considering the basic policy on handling of ALPS treated water decided by the government in April. It has also been reviewing details of the design and operation of facilities for securing safety “with a view to taking thorough actions to minimise adverse impacts on reputation”.
One of the ways Tepco hopes to increase confidence in its water treatment policy is through a rearing test of marine organisms, It plans to rear marine organisms in seawater containing ALPS treated water to show that the level of tritium in those organisms does not become more concentrated than the seawater tritium level. Tepco is also investigating possible methods for removing tritium from the water and has selected Nine Sigma Holdings as “the third-party partner for securing transparency regarding eliciting proposals and promoting wide-scale research on tritium separation technology”.
An open call webpage was setup in the company website, and research and reception of proposals on tritium separation technology both domestic and abroad has been initiated. Proposed technologies proposed will be evaluated by Nine Sigma Holdings and the results will then be examined by Tepco. “If it turns out that the technology is able to be realistically applied to ALPS treated water, etc., detailed designs will be drawn up and verification tests of the technology will be conducted,” Tepco noted.
Photo: Recent view of the Fukushima Daiichi site (Photo credit; TEPCO)