HEPS光束线站光学棚屋辐射屏蔽设计

Design of Radiation Shielding for Optical Enclosure at HEPS Beamline Station

  • 摘要: 高能同步辐射光源(high energy photon source,HEPS)是一台能量为6 GeV、流强为200 mA的第4代同步辐射装置,建成之后将是我国拥有的第一台高能同步辐射光源。HEPS可以提供高达300 keV能量的X射线,具备建设80条以上高性能光束线站的容量。光束线站运行过程中不可避免地产生有害辐射,成为光源运行及维护过程中工作人员辐射剂量的直接来源。因此,采用棚屋整体屏蔽的方式包容有害辐射是很有必要的。光学棚屋作为光束线站中辐射最严重的区域,数量多达几十个,如何在满足防护需求的同时探索出可以灵活应用于各线站的屏蔽设计方案成为光束线站建设中亟待解决的问题。本文基于线站结构特点及源项类型,重点分析了光学棚屋内的辐射源项类型并提出了标准化屏蔽设计方案。结合束线设备种类及其布局,采用蒙特卡罗程序FLUKA和同步辐射计算软件STAC8模拟了光学棚屋内剂量分布及在屏蔽体内的衰减,给出了光学棚屋屏蔽墙体的建议厚度。合理的光学棚屋屏蔽体厚度可为HEPS束线提供辐射防护设计的依据。

     

    Abstract: High energy photon source (HEPS) is one of the major scientific and technological infrastructure in the 13th Five-Year Plan of China. HEPS is a 6 GeV, 200 mA fourth-generation synchrotron light source. HEPS is capable of emitting X-rays up to 300 keV in energy and can build more than 80 advanced beamline stations. After completion, it will be the first high-energy synchrotron source owned by China. Beamline stations are used for producing, processing, and analyzing synchronous radiation. At beamline stations, harmful radiation inevitably generated directly determine the occupational radiation exposure (ORE) during operation and maintenance of HEPS. Radiation protection of beamline stations forms a crucial aspect of HEPS construction. Optical enclosures are the zone receiving the highest levels of radiation at each beamline station, with numerous optical enclosures present in HEPS. How to meet protection requirements while exploring flexible shielding design solutions that can be applied to various beamline stations has become an urgent problem to be solved. This paper studied the key issues of radiation protection in optical enclosures at HEPS beamline stations and conducted a structured design for radiation protection. Initially, an analysis was conducted on the structural features and the source term of beamline stations. The beamline stations were categorized into three distinct types: bending magnet, undulator, and wiggler. Items from radiation sources were categorized into two distinct types: gas bremsstrahlung and synchrotron radiation. The optical enclosures were standardized and categorized according to their structural features and the type of source item. Standardization involved determining the most intense radiation conditions at a similar type of beamline station. The outcomes of these calculations served as a benchmark for other beamline stations of a similar nature. For the gas bremsstrahlung, the equipment layout of the typical beamline station was introduced from the perspective of radiation protection. Attenuation of radiation dose in the shield was analyzed by Monte Carlo code FLUKA. An analysis was conducted on the correlation between the dose of gas bremsstrahlung and the shielding thickness. For synchrotron radiation, the synchrotron radiation spectrum of HEPS beamlines was calculated by STAC8 code. The influence of synchrotron radiation scattering angle was analyzed. Attenuation of synchrotron radiation dose in the shield was analyzed by STAC8. An analysis was conducted on how synchrotron radiation dosage correlates with the shielding thickness. Results from the calculations indicate a pattern where the dose rate from gas bremsstrahlung initially rises and subsequently falls within the back wall. The reason lies in the fact that gas bremsstrahlung’s dispersed photons maintain a specific forward alignment and engage in photonuclear reactions to generate neutrons on the back wall. With the scattering target tilted at 45°, the highest synchrotron radiation dose rate beyond the shielding wall is between 40° and 60°. The radiation dose rates on the side and back walls primarily originate from gas bremsstrahlung, whereas those outside the roof are chiefly from synchrotron radiation.

     

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