Abstract: The radiation source term of the 3 m³ transport container for natural uranium hexafluoride, after full load and unload, is analyzed. The external radiation level of the container is simulated and calculated, so as to provide suggestions for the optimization of radiation protection during the operation and transportation of the container package. The results show that the external γ radiation of the container comes from ²³⁵U, ^234mPa and ²³⁴Pa; When the package is fully loaded, the external radiation level increases with time until the third month; After the container is unloaded, due to the lack of self-shielding of UF₆ and the large residue of decay daughters ²³⁴Th, ^234mPa and ²³⁴Pa, the external radiation level of the container is even higher than the full load package. The maximum radiation levels on the container surface decreased from 167.5 μSv·h^-1 down to 30.3 μSv·h^-1 at the first two months.The surface radiation level of unloaded container was measured after two months and the maximum value was 31.3 μSv·h^-1 and 28.1 μSv·h^-1 respectively. The measured results are consistent with the calculated results, which proved the presumption of the distribution of residual UF₆ is correct. In view of the frequent natural UF₆ transportation activities and large transportation volume, the radiation protection for the residual containers should not be ignored. The exposure of workers can be reduced by increasing the vacant time of residual containers, remote operation and reducing the operation time.

Key words: uranium hexafluoride, radiation level, transport, package