10MW高温气冷实验堆(HTR-10)的燃耗测量系统通过测量燃料球内裂变产物¹³⁷Cs发出的γ射线进而间接确定燃料球的燃耗,测量结果的准确性直接影响着反应堆的安全性和经济性。利用HTR-10现有的设备条件,设计并实施了提升器偏转实验,使燃料球逐步偏离正常测量位,改变球心与准直器轴线的相对位置,得到了偏离角度与计数率之间的对应关系,进而确定燃料球球心与准直器轴线的周向偏移量。通过MCNP程序建立HTR-10燃耗测量系统模型,模拟γ光子从燃料球发出,经过提升器、密封法兰、准直器直到被HPGe晶体探测器捕捉的全过程。利用MCNP模型可以模拟在不同径向偏离情况下的实验过程,通过与实验结果的对比,确定燃料球球心偏离准直器轴线的径向偏移量。

With the burn-up measurement system for the 10MW high temperature gas-cooled reactor, the burn-up of the spherical fuel element is obtained indirectly by measuring the gamma-ray from the fission product ¹³⁷Cs. The accuracy of results will affect the security and the economy of the reactor. In this paper, on the basis of the existing equipment conditions of HTR-10, the diversion experiment of the elevator is designed and implemented. By making the spherical fuel element gradually deviate the running measurement place, the relative position between the center of the spherical fuel element and the axis of the collimator is changed. and the relationship between the angle of the diversion and the count rate is obtained and is then used to determine the offset in the circumferential direction between the center of the spherical fuel element and the collimator axis. The model of the HTR-10 burn-up measurement system, established by the MCNP program, can be used to simulate the gamma photon transporting process from the spherical fuel element, through the elevator, the sealed flange and the collimator, to the HPGe detector. The MCNP model can be used to simulate the experiment in different radial deviations. By analyzing the experiment results and calculating results of the MCNP model, the radial diversion from the core of the spherical fuel element to the axis of the collimator can be estimated.