The Japanese government has taken actions in accordance with the documents of international organizations regarding the release of treated water containing radioactive materials into the environment, and these actions have been confirmed by international organizations.
In order to minimize the impact on the surrounding environment and the reputational damage, Japan has set a maximum tritium concentration (1,500 Bq/l) for the discharge and a total annual tritium discharge limit (22 TBq per year).
Note: The dose due to effluent water assumes that 2 liters of effluent water with the maximum discharge limit and the highest concentration of the sum of the ratios to the concentration limits of each nuclide were drunk daily at the drain.
This concentration applies to any liquid discharged from the Fukushima Daiichi Nuclear Power Station based on its independent on-site analysis.
In designating Fukushima Daiichi NPS as a Specific Nuclear Facility additional effective dose at the site boundaries should be less than 1 mSv/y, considering "dose due to direct and skyshine radiation," "dose due to gases," and "dose due to liquids"
Effective dose from effluent water is the sum of:
* water discharge (0.22mSv/y; discharged water such as bypassed groundwater and subdrain treated water) and
* water sprinkle within the site (0.075mSv/y; sprinkled water such as rainwater and treated Unit 5/6 stagnant water).
According to Japanese rules, the concentration of tritium in effluent water is 60,000 Bq/l
The radioactive concentration limit for tritium in effluent water discharged from facilities in Japan is 60,000 Bq/l.
60,000 Bq/l is the concentration that would result in a committed effective dose of 1 mSv for one year of ingestion if 2 l of water at that concentration were drunk every day.
Suspension Level for Discharge is 700 Bq/l at vicinity of the discharge point (10 points within 3 km of the discharge point at FDNPS) and 30 B/L at outside the vicinity of the discharge point (4 points in a 10 km x 10 km area around the discharge point)
Existing exposure situation or planned exposure situation
Japan has not incorporated dose constraints into its laws and regulations.
Dose constraints is not a concept that applies to existing exposure situations.
The relevant international safety standards require the establishment of dose constraints as part of the process for optimization of protection for any planned exposure situation. For the discharge of the ALPS treated water, the establishment of a prospective and discharge-related restriction on the individual dose attributable to the discharge, provides a basic level of protection for the most highly exposed individuals due to the discharge, and serves as an upper bound on the dose in the optimization of protection for the discharge.
After discussions between the Task Force and METI/TEPCO during the first mission, the Task Force noted that the concept of a dose constraint does not exist in Japanese law.Following discussions with the Task Force, NRA confirmed that the criterion of 0.05 mSv per year established by NRA for the discharge of ALPS treated water – which is the operational target for nuclear power stations in Japan – could be interpreted as a dose constraint. Paragraph 5.16 of GSG-9 [9] states that “in practical terms, dose constraints should be selected within the range of 0.1 to less than 1 mSv in a year”. With this in mind, the Task Force noted that the selected dose constraint of 0.05 mSv per year is below this range and is therefore conservative.
The Government of the Hong Kong Special Administrative Region
