放射源库设计与屏蔽计算

Design and shielding calculation of radioactive source storehouses

针对放射源安全贮存的现实需求,本文根据现有放射源类型对放射源库进行了设计,其中非豁免类γ源与中子源采用1 m深地坑存放,α源、β源及豁免源采用铁质保险柜存放。考虑到放射源库位于实验楼内,对辐射防护进行了充分的保守设计,通过理论计算,对坑盖、墙体、活动屏蔽块的材料与尺寸等参数进行了设计。采用蒙特卡罗模拟计算对理论设计进行复核,并准确获得放射源库辐射水平。结果表明:γ源源坑配套5 cm厚铁坑盖,中子源源坑配套20 cm厚含硼聚乙烯坑盖,源库间墙体采用20 cm厚混凝土,能够使源库间内部最大比释动能率低于25μGy/h,高1 m处的最大比释动能率为1.5μGy/h左右,而源库间外比释动能率同本底水平相当,不但充分满足了放射源贮存相关标准要求,还确保了放射源库周边办公区域人员的辐射安全。

The radioactive source storehouses are designed in accordance with the types of radioactive sources in the institute to meet the practical requirements for the safe storage of radioactive sources.In the institute,the nonexempt-edγ-source and neutron source are stored in the 1 m deep pit,andα,βand exempted sources are stored in an iron safe.The radioactive source storehouse is designed to be located in the laboratory building.Thus,radiation protection is designed conservatively.First,the material and size parameters of the pit cover,as well as the wall and movable shield block,are designed on the basis of theoretical calculation.The theoretical design is then rechecked through MCNP simulation calculation,and the radiation level of the radioactive source storehouses is obtained accurately.Re-sults show that when theγsource-reservoir is covered with a 5 cm thick iron pit cover,the neutron source-reservoir is covered with a 20 cm thick boron-containing polyethylene pit cover,and the wall between the source and reservoir is covered with 20 cm thick concrete,the maximum internal kerma(kinetic energy released per unit mass)of the source-reservoir is less than 25μGy/h,the maximum kerma at the height of 1 m is approximately 1.5μGy/h,and the external kerma between source and reservoir is equivalent to the background level,respectively.These conditions not only fully meet the requirements of relevant standards for the storage of radioactive sources but also ensure the safety of personnel against radiation in the office area around the radioactive source warehouses.