Development of residual radioactive levels in decommissioned final soil

This study introduces the process and methodology for determining residual radioactive levels in soil at a decommissioned nuclear facility site. Drawing on current research into decommissioned sites both domestically and internationally, this study reviews the approaches adopted by the International Atomic Energy Agency, the USA, and China for defining decommissioning end-state targets and establishing dose constraint values. A source investigation of soil pollution was first conducted to identify the types and quantify the activity concentrations of key pollutants. Subsequently, the radiological assessment defined decommissioning goals and dose constraints, identified exposure pathways and key parameters under open, unrestricted land-use scenarios, and developed an assessment model to calculate the effective dose using a forward calculation approach. By using the open-limit conversion method for reverse calculation, the residual radioactive level of the decommissioned final soil is ultimately determined. The allowable residual activity concentration values for three nuclides were calculated. The allowable residual activity concentration value for ^{60}\mathrm{Co} was 1.9 \cdot 10^{2} \, \mathrm{Bgkg^{-1}} , the allowable residual activity concentration value for ^{137}\mathrm{Cs} was 8.4 \cdot 10^{2} \, \mathrm{Bgkg^{-1}} , and the allowable residual activity concentration value for ^{90}\mathrm{Sr} was 1.1 \cdot 10^{5} \, \mathrm{Bgkg^{-1}} . The final determination of the allowable residual activity concentration values for the three nuclides will provide a basis for implementing, supervising, and accepting decommissioned engineering projects.