The spherical fuel elements are adopted in the high-temperature gas-cooled reactor pebble-module (HTR-PM). The fuel elements will be discharged continuously from the reactor core and transported into the fuel transport pipelines during the reactor operation, leading to spatially varying dose outside the pipeline. In this case, the dose evaluation faces two major challenges, including dynamic source terms and pipelines with varying lengths and shapes. This study tries to handle these challenges for HTR-PM through comprehensive calculations using the QAD-CGA program and to design the corresponding shielding of the pipeline. During the calculation, it is assumed that a spherical fuel element stays in different positions of the pipelines in turn, and the corresponding dose contributions were calculated. By integrating the dose contributions at different positions, the dose at the points of interest can be obtained. The total dose is further determined according to the assumed fuel elements transport speed of 5 m/s and total 6000 fuel elements transportation per day. Two types of fuel transport pipelines and two source terms were considered, i.e., the spent fuel element transport pipelines with corresponding spent fuel source term and the different burn-up fuel element transport pipelines with the average burn-up fuel source term. Doses at different points of interest were calculated with no shielding scenario and with lead shielding of different thicknesses scenario. To evaluate the shielding effect, the dose limit of the orange radiation zone of HTR-PM and the radiation damage thresholds from NCRP report No.51 were both adopted. The calculated results show that, for pipelines that transport the spent fuel, a 4 cm lead shielding will be enough. And for pipelines that transport fuel elements with different burn-up, a 5 cm lead shielding will be added. The method and results can provide valuable reference for other work of HTR-PM.

中文翻译：

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QAD-CGA程序对HTR-PM燃料运输管道的屏蔽设计和剂量评估

球形气体燃料元件用于高温气冷反应堆卵石模块（HTR-PM）。燃料元素将从反应堆堆芯连续排出，并在反应堆运行期间输送到燃料输送管道中，从而导致管道外部的剂量发生空间变化。在这种情况下，剂量评估面临两个主要挑战，包括动态源术语以及长度和形状不同的管道。本研究试图通过使用QAD-CGA程序进行综合计算来应对HTR-PM的这些挑战，并设计相应的管道屏蔽。在计算过程中，假设球形燃料元件依次停留在管道的不同位置，并计算出相应的剂量贡献。通过积分不同位置上的剂量贡献，可以获得感兴趣点处的剂量。根据假定的5 m / s的燃料元件运输速度和每天总共6000个燃料元件运输速度进一步确定总剂量。考虑了两种类型的燃料输送管道和两个源项，即，具有对应的乏燃料源项的乏燃料元件输送管道和具有平均燃尽燃料源项的不同的燃耗燃料元件输送管道。在没有屏蔽的情况下和在不同厚度的铅屏蔽情况下计算了在不同关注点的剂量。为了评估屏蔽效果，采用了HTR-PM橙色辐射区的剂量限值和NCRP报告No.51的辐射损伤阈值。计算结果表明，对于运输乏燃料的管道，4 cm的铅屏蔽层就足够了。对于运输燃耗不同的燃料元件的管道，将添加5 cm铅屏蔽层。该方法和结果可为HTR-PM的其他工作提供有价值的参考。