According to Fig. 1a, when Eu-152 is detected in the results of radiochemical analysis, it can be classified as an activated structural material. Conversely, when Eu-152 is not detected, it can be classified as a surface contaminant. This classification also allows for a rational assessment of Ni-63, distinguishing whether its presence is due to radioactivity or contamination (Fig. 1b).

We plan to dispose radioactive wastes generated from research, industrial, and medical facilities at a near-surface disposal site. The radioactivity concentrations in these wastes must be confirmed to be below the national standards for key radioactive nuclides. However, when it is difficult to distinguish whether the waste is an activated material or contamination, the estimated radioactivity concentrations may be overestimated. To establish a rational evaluation method of radioactivity concentrations, distinguishing contamination sources is vital.

In this study, we investigated evaluation methods such as the theoretical calculation method, scaling factor method, and mean radioactivity concentration method for key radioactive nuclides in concrete waste generated from the dismantling of the Japan Power Demonstration Reactor. We focused on the gamma-ray emitting nuclides Eu-152 and Co-60, which can be externally measured, and explored their potential in distinguishing contamination sources. Results indicate that selecting an appropriate evaluation method for each nuclide enables a rational assessment of radioactivity concentrations in the waste.

Aono, R. et al., Study on the Evaluation Methodology of the Radioactivity Concentration in Low-Level Radioactive Concrete Wastes Generated from JPDR, JAEA-Technology 2024-006, 2024, 48p. (in Japanese).

Paper URL: JAEA-Technology-2024-006.pdf

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