摘要: 由中国科学院近代物理研究所负责设计和建设的加速器驱动嬗变研究装置（CiADS）将建于广东省惠州市。作为一个核装置，CiADS在运行过程中会对环境造成次级放射性影响，因此评估CiADS对环境造成的次级放射性影响水平不仅对公众健康有重要意义，对屏蔽设计也具有一定的指导作用。利用²⁴¹Am-Be中子源对兰州重离子加速器研究装置（HIRFL）附近的卵石材料进行了辐照实验，测量和分析了辐照后卵石样品内产生的²⁴Na，⁵⁴Mn，⁵⁶Mn和²⁷Mg的比活度等相关信息。通过对实验数据与利用蒙特卡罗程序Geant4模拟得到的各放射性核素比活度的比较，验证了Geant4模拟分析中子场下环境介质次级放射性这一方法的可靠性。进而利用Geant4模拟研究了CiADS质子加速器HEBT隧道底部屏蔽层外的中子能谱以及隧道底部屏蔽层外卵石层因中子活化产生的主要放射性核素的饱和比活度。分析结果表明，在合理的屏蔽设计条件下，CiADS运行期间泄露到屏蔽层外的中子活化环境中卵石材料造成的环境影响几乎可以忽略。


The China initiative Accelerator Driven System (CiADS) is the first integrated ADS facility designed to study the safety disposal of nuclear waste. As a nuclear facility, it will cause radiological impact on the environment. Therefore, the assessment of radiological impact on the environment around this facility will not only meaningful to the public health, but also offers significant guides to the shielding design of CiADS. Pebble samplings were collected around the campus of the Heavy Ion Research Facility in Lanzhou (HIRFL) and irradiated by a ²⁴¹Am-Be neutron source. Based on the γ-spectrum measured by a HPGe detector before and after the neutron irradiation, the specific activities of induced radionuclides ²⁴Na,⁵⁴Mn,⁵⁶Mn and ²⁷Mg in these samples were analyzed and compared with the Monte-Carlo simulation values obtained with the Geant4 toolkit. The comparison between the experimental and simulated results indicates that Geant4 toolkit is feasible for radiation impact assessment of nuclear facilities, such as CiADS. Then the neutron spectrum outside the concrete shielding of HEBT tunnel of the CiADS have been simulated by the Geant4 toolkit, and the saturation activities of the induced nuclides in the first 10 cm pebble layer have been predicted. The results show that the saturation activities of induced radionuclides in pebbles outside the CiADS shielding are much lower than their exemption values and their radiation impacts to the environment could be ignored.