Currently about 70% of the water stored in the tanks contains radioactive materials other than tritium, at concentrations in excess of regulatory levels. This is the result of actions taken to quickly minimize the impact of radiation on surrounding communities. As such, priority was given to water treatment processes that maximized processing quantities.
Before being discharged, the water will be retreated until the concentrations of the other radioactive materials are reduced to below regulatory clearance levels. While tritium will remain in the water, it will be diluted to concentrations below clearance levels once the water is discharged into the ocean. In a similar way, the other materials already within clearance-level concentrations will be diluted to lower concentrations still, which in turn offers additional peace of mind.
*In September 2020, TEPCO conducted an experiment to evaluate the performance of ALPS secondary treatment. Results confirmed that the concentrations of radioactive materials could be reduced, and that the sum of the concentration ratios for all radionuclides (excluding tritium) could be brought to below 1 through secondary treatment. (The sum of the concentration ratios for 62 radionuclides and carbon-14 based on tests conducted on the J1-C tank group: before secondary treatment = 2,406; after secondary treatment = 0.35.)