Abstract: A derivation method and process of activity concentration upper limits are introduced in this paper. It is for low level solid radioactive wastes at any time before and after the three-hundred-year surveillance period in near surface disposal facilities when their radiation doses are less than the dose limits for individual public or intruders through various exposure pathways. Taking Yaotian disposal site and Beilong disposal site as reference sites, the radionuclide transfer processes and exposure pathways of various scenarios following the closure of disposal facilities are analyzed based on basic safety requirements for near surface disposal of radioactive wastes. Their conceptual model and mathematical model of radionuclide transfer are established, and effective doses to human from various scenarios are calculated. Under the assumption of a linear relationship between activity concentration and dose rate, the activity concentration upper limits of various scenarios are derived for each radionuclide meeting dose criteria. The smallest upper limit is selected to determine the magnitude of upper limits of activity concentration for each radionuclide in low level solid radioactive wastes.

Key words: low level radioactive waste, activity concentration upper limit, derivation, near surface disposal