TEPCO, Japan’s largest power company group, has released a report which outlines two potential methods for disposing of water treated with multi-nuclide removal equipment, that is currently being stored at the damaged Fukushima Daiichi nuclear power plant.
The International Atomic Energy Agency (IAEA) published a review last week which concludes that the two options presented by TEPCO – discharge into the sea and vapour release – are technically feasible. Additionally, the methods are used routinely at operating nuclear plants around the worldwide, under specific regulatory authorisations based on safety and environmental impact assessments.
Following the 2011 tsunami at the nuclear power plant which led to the meltdown of three reactor units, the melted reactor cores continue to require cooling to remove excess heat. Due to damaged integrity of reactor vessels, radioactive water accumulates inside the reactor and turbine, for which TEPCO installed radioactive water treatment systems.
As of 12 March, the site stores 979 tanks containing a total of about 1.19m m3 of treated water. The water has been treated using TEPCO’s advanced liquid processing system (ALPS), a multi-nuclide removal system which removes all radioactive substances excluding tritium – which releases weak radiation – and it has additionally been treated to remove strontium. Currently, there are a total of 1,005 tanks on site with more to be constructed by the end of 2020. The construction will increase the site’s tank capacity to approximately 1.37m m3.
Of five options explored to dispose of the treated water, the report considers two of them – discharge into the sea, and vapour release – as “practical options, both of which have precedent in current practice. For discharge into the sea, the water would be further treated to reduce radioactive substances before it is diluted with seawater and released. To enable vapour release, water would also receive secondary treatment before being vaporised, diluted with air, then released.
Tritium concentration would be diluted to below the regulatory concentration limit of 5 Bq/L in air and less than 1,500 Bq/L in water, about the level of operational standards for groundwater bypass and subdrains. The amounts are much lower than the regulatory concentration limit for tritium in seawater, 60,000 Bq/L. “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,” says the report.
According to the report, the other options – geosphere injection, hydrogen release, and underground burial – “come with too many unresolved issues in consideration of their use with regard to regulations, technology, and time”. IAEA said the two options outlined were based on a comprehensive and scientifically-sound analysis addressing the necessary technical, non-technical and safety aspects.
The Japanese Government has the final authority to decide which disposal policy to implement. It will continue to consider options for disposing of ALPS-treated water and communicate with stakeholders regarding the matter. TEPCO says it will continue to share information regarding the decontamination and decommissioning of the Fukushima Daiichi site, and cooperate with the Government as it works towards a final decision, while “always keeping safety as top priority”.
Once the Government decides on its preferred method of disposal, IAEA says it is ready to work with Japan to provide radiation safety assistance before, during, and after disposal. The Japanese Government and IAEA have been cooperating extensively over the past decade to deal with the Fukushima Daiichi accident, in areas such as radiation monitoring, remediation, waste management and decommissioning.
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