Tepco outlines treated water disposal options

As of 12 March, some 1.19 million cubic metres of treated water are stored within 979 tanks on the plant site. This includes contaminated water that has been treated by the Advanced Liquid Processing System (ALPS), which removes most of the radioactive contamination, with the exception of tritium. It also includes water that has been treated to remove strontium. The average tritium concentration of the stored water is about 730,000 becquerels per litre. Total tritium contained within the stored water is about 860 trillion Bq.

A Japanese government subcommittee considered the options available to Tepco for disposing of this water as storage space at Fukushima Daiichi is nearing full capacity. The committee looked at five options: geosphere injection, discharge into the sea, vapour release, hydrogen release, and underground burial. Of these, geosphere injection, hydrogen release and underground burial were considered to come with too many unresolved issues in consideration of their use with regard to regulations, technology and time. "For these reasons, discharge into the sea and vapour release are the practical options, both of which have precedent in current practice," the subcommittee concluded. It noted that the radiation impact of both options is "notably small, compared to natural radiation exposure".

Tepco released its own "conceptual study" on the two disposal methods on 24 March. The company said its report "can serve as a reference for the general public and the parties concerned", including those who plan to participate in the government-organised "opinion hearings". The report also covers measures being taken by Tepco to strengthen the Fukushima area's reputation, including achievements to date and future plans.

"Regardless of the disposal method, Tepco will not only comply with legal requirements, but will also take initiatives to suppress reputational damage," the company said.

Tepco noted that the annual tritium release rate "will be set by referencing those of the existing nuclear facilities and making effective use of the period of 30 to 40 years required for decommissioning, instead of releasing a large amount at once." Tepco said the amount of radioactive materials other than tritium will be reduced as much as possible, while the tritium concentration will also be lowered as much as possible.

For vapour release, Tepco said it will study dilution of tritium at a rate equivalent to that for discharge into the sea, as against the regulatory concentration limit of tritium in the atmosphere (5 Bq in 1 litre of air). For discharge into the sea, the company will study dilution rates of tritium with reference to operational standards for 'groundwater bypass' and 'subdrains' (1500 Bq in 1 litre of water), which are well below the regulatory concentration limit for tritium in seawater (60,000 Bq in 1 litre of water).

Tepco noted that the government, not the company, has the final authority to decide which disposal policy to implement.

"Going forward, the government will continue to consider the options for disposing the ALPS-treated water and communicate with stakeholders regarding this matter," Tepco said. "Tepco will continue to actively share information regarding Fukushima Daiichi's decontamination and decommissioning as well as cooperate closely with the government as it works toward its final decision, always keeping safety as the top priority."