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The Subdrain System is a group of wells installed near the reactor and turbine buildings.
It is expected that the amount of groundwater flowing inside the reactor and turbine buildings will be greatly reduced by the Subdrain System pumping up groundwater. Additionally, groundwater flowing in on the sea-side will be pumped up by the dam installed on the sea-side impermeable wall and the well (Groundwater Drain) installed in the embankment.

* TEPCO will never discharge the water into the ocean without the understanding of the relevant ministries and the fishing industry.

Work Steps from Pumping up to Discharge

  • *1:

    These specialized water purification facilities are capable of reducing the concentrations of radioactive materials (except for tritium) from approximately 1/1,000 to 1/10,000.

  • *2:

    TEPCO and third party organizations will ensure that the water meets the more stringent water quality standards (TEPCO's upper concentration limits) than the ones set for the groundwater bypass operations.

  • *3:

    TEPCO will never discharge the water into the ocean without the understanding of the relevant ministries and the fishing industry.

Purification Process and Analysis Standards

In order to purify the groundwater, the concentrations of cesium and strontium are reduced in two purification steps.
Water is discharged only after confirming that the concentrations of cesium-134, cesium-137, Gross β (strontium, etc.) and tritium do not surpass TEPCO's upper concentration limit and that other γ nuclides are not detected.

  • *4:

    Should the concentrations of cesium and Gross β be over TEPCO's upper concentration limit, the purification process will be repeated.
    If the concentration of tritium in water collecting tanks before purifying exceeds TEPCO's upper concentration limits, TEPCO will transfer the water to storage tanks or similar facilities on the nuclear power station premises to prevent highly contaminated water from being discharged into the ocean.

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