Through previous analyses, TEPCO has selected nuclides present in significant concentrations in contaminated water as “nuclides subject to measurement/assessment*.” Before each discharge of ALPS treated water into the sea, we confirm that the aforementioned nuclides, excluding tritium, meet the standards for environmental discharge with our measurement/confirmation facility. However, the concentration of radioactive substances in contaminated water may change over prolonged periods of decommissioning work. This is why we monitor annually to see if nuclides, which could theoretically exist but were confirmed through previous analyses that they are not at significant concentration levels in contaminated water (monitoring-target nuclides), are present in significant concentrations.
In a February 2024 survey, we detected 2.9 Bq/L (regulatory concentration limit: 40 Bq/L) of cadmium-113m in the pre-ALPS-treated contaminated water (water sampled at the ALPS inlet), from among the six monitoring-target nuclides (chlorine-36, niobium-93m, niobium-94, molybdenum-93, cadmium-113m, and barium-133). Cadmium-113m is a nuclide removable through ALPS. However, in response to its detection and based on an implementation plan approved by the Nuclear Regulation Authority, starting with the fourth ALPS treated water discharge into the sea in FY2024 we added cadmium-113m to our “nuclides subject to measurement/assessment,” which are measured with the measurement/confirmation facility each time ALPS treated water is discharged into the sea.*1
We have had an arrangement to voluntarily measure 39 nuclides including cadmium-113m before discharging ALPS treated water into the sea, and had confirmed in each discharge that the concentration of cadmium-113m was less than the regulatory concentration limit (40 Bq/L). Previously discharged ALPS treated water therefore poses no safety issues.*2
We will ensure safety for the discharge of ALPS treated water into the sea by continuing to thoroughly confirm with our “measurement/confirmation facility” that the concentration of nuclides subject to measurement/assessment is reliably below the regulatory standard value for environmental discharge.
*1 See this Q&A for “nuclides subject to measurement/assessment.”
Treated Water Portal Site: Q&A
“During the discharge of ALPS treated water into the sea, what is being measured in the “measurement/confirmation facility”?” *2. Click here to see the results of 39 nuclides, including cadmium-113m, measured for the fourth discharge of FY2024.
https://www.tepco.co.jp/en/hd/decommission/data/analysis/pdf/2024/measurement_confirmation_240805-e.pdf Click here to see the results of measurements taken with the measurement/confirmation facility prior to the third discharge of FY2024.
Third discharge, FY2024
Second discharge, FY2024
First discharge, FY2024
Fourth discharge, FY2023
Third discharge, FY2023
Second discharge, FY2023
First discharge, FY2023