Analysis of 1F Waste at Laboratory-1, Okuma Analysis and Research Center (Annual Activity Report, FY2024)

Okuma Analysis and Research Center

This report summarizes the objectives, methods, and results of analyses of Fukushima Daiichi (1F) waste (hereinafter 1F waste) conducted in FY 2024 at the Radioactive Material Analysis and Research Facility (hereinafter Laboratory-1) of the Okuma Analysis and Research Center. The waste samples analyzed included rubble concrete, soil, incineration ash, secondary wastes obtained from wastewater treatment (e.g., carbonate slurry and iron co-precipitation slurry), rubble metal, and decommissioning debris. Ten key radionuclides in the analysis plan specified by TEPCO - Co-60, Cs-137, Sr-90, Ni-63, Pu-238, Am-241, Cl-36, Tc-99, I-129, and C-14 - were quantified. Since 2024 was the first full year of routine operation at Laboratory-1, the analyses aimed not only to obtain data needed for understanding waste characteristics and supporting safety assessments of waste treatment and disposal, but also to verify the applicability of analytical methods to diverse sample matrices. Accordingly, this report evaluates both analytical results and the effects of sample matrix differences on analytical method performance. Since its establishment and commencement of operations, the Okuma Analysis and Research Center has developed rapid analytical methods for 1F waste and initially validated the developed methods using concrete as the primary waste matrix. In FY 2024, these methods were applied to a broader range of samples. Method validation confirmed that the developed analyses were not affected by co-existing radionuclides and that the achieved detection limits aligned with the regulatory concentration requirements for trench disposal. All sample types satisfied the validity criteria, demonstrating the applicability of the developed methods to the targeted sample matrices. Accordingly, matrix effects were assessed by evaluating chemical separation recovery and its reproducibility, which was expressed as standard deviations. The obtained results showed that for most matrices and radionuclides, the developed methods resulted in good recovery and reproducibility, comparable to concrete, except for the reduced recovery of Cl-36 in soil and incineration ash. Although the detection limits can be improved to a certain level by lengthening the measurement time, such improvements may not always meet low-level detection requirements; therefore, the need to improve these analytical methods was discussed.