3m^(3)天然六氟化铀运输货包满载及卸载后的辐射水平分析北大核心CSCD

对运输天然UF_(6)原料的3 m^(3)运输容器在满载和卸料后容器内部的辐射源项及分布情况进行分析,计算两种状态下容器表面及1 m处辐射水平,并与实际测量结果进行了对比。计算结果表明:容器外部辐射主要来源于^(234)m Pa、^(234)Pa和^(235)U的γ辐射;满载时,容器外部辐射水平随时间增加而增加,至3个月时基本达到稳定;卸料后,残料容器中由于衰变子体^(234)Th、^(234)m Pa和^(234)Pa的大量残留,且缺少UF_(6)的自屏蔽作用,容器外部辐射水平高于满载状态,在卸料后2个月,残料容器表面最大辐射水平从167.5μSv·h^(-1)降到30.3μSv·h^(-1)。对卸料后约2个月的两个3 m^(3)运输容器表面辐射水平进行测量,测得最大辐射水平分别为31.3μSv·h^(-1)和28.1μSv·h^(-1),测量结果与计算结果基本一致。鉴于天然UF 6运输活动频繁,运输量大,因而在残料容器返厂运输活动中的辐射防护不容忽视,可通过增加残料容器空置时间、远距离操作和减少操作时间来减少工作人员遭受的照射。

Analysis and evaluation of radiation level of the loaded and unloaded package of 3 m3 natural uranium hexafluoride for transport

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.