Journal of Nuclear Fuel Cycle and Waste Technology

Clearance serves as a regulatory mechanism to reduce unnecessary restrictions, lower economic costs, promote recycling of metallic resources, minimize decommissioning expenses, and improve efficiency of radioactive waste disposal facilities. In South Korea, clearance is determined by compliance with clearance dose or clearance level (CL). However, CLs for uranium isotopes (²³⁴U, ²³⁵U, ²³⁸U) have not yet been established, requiring case-by-case dose assessments and creating administrative challenges. In this study, CLs for uranium isotopes were derived using the methodology of IAEA SRS No. 44 and scenarios tailored to domestic conditions. The IAEA based evaluation produced CLs of 1 Bq·g⁻¹ for all three isotopes, whereas domestic assessments yielded 1 Bq·g−1 for ²³⁴U and ²³⁸U and 0.1 Bq·g⁻¹ for ²³⁵U. Because uranium isotopes typicallyoccur as mixtures, the derived values were further applied to depleted uranium (DU), natural uranium (NU), and low enriched uranium (LEU). A comparison between a uniform 1 Bq·g⁻¹ assumption and the case applying 0.1 Bq·g⁻¹ to ²³⁵U revealed increases in summed fractions of 10%, 20%, and 26% for DU, NU, and LEU, respectively. Considering conservative assumptions in both scenarios and input parameters, a uniform CL of 1 Bq·g⁻¹ for ²³⁴U, ²³⁵U, and ²³⁸U is recommended as reasonable and technically justified.

Keywords

Clearance level, Dose assessment, Uranium isotopes, NORM, ²³⁴U, ²³⁵U, ²³⁸U