【作者】 闫威华；

【导师】 肖志刚；

【作者基本信息】 清华大学 ， 物理学， 2013， 博士

【摘要】 作为球床模块式反应堆中燃料元件循环的重要组成部分，燃耗测量系统必须对连续排出堆芯的燃料球进行非破坏性在线测量，以确定是作为乏燃料球退出循环，还是将其返回堆芯。¹³⁷Cs的活度和燃耗值存在很好的单调对应关系，因此高温气冷堆核电站示范工程将利用高纯锗探测器测量燃料球中¹³⁷Cs的活度，进而根据燃耗计算曲线确定其燃耗值。在10兆瓦高温气冷试验堆等以前的高温气冷堆上也曾运行过类似的系统，但是在高温气冷堆核电站示范工程中由于冷却时间和测量时间更短，情况更为复杂，具体表现在能谱成分非常复杂，且本底活度很大，必须重新审视其可行性。本文取得的研究结果如下：首先优化了高纯锗谱仪的工作参数，使之能在强本底下仍能有很好的能量分辨率，从而能将¹³⁷Cs的全能峰从其周围的干扰峰中分辨出来，同时也确定了准直器及屏蔽体等的设计。接着，用⁶⁰Co和¹³⁷Cs源分别模拟反应堆运行时真实情况下的本底和全能峰计数率，利用实验谱优化了谱分析的算法和参数，最终对具有典型深燃耗值的燃料球中¹³⁷Cs的全能峰净面积，相对误差能达到2.8%（1σ）。由于没有可供刻度用的燃料球，我们采用了在中心放置点源的石墨球来做标准源，在模拟和实验吻合的基础上，借助效率传递方法得到由于自吸收的影响导致的修正因子为1.07±0.02（p=0.95）。在探测器及其他几何条件都确定之后，我们利用KORIGEN计算得到燃料球中的核素活度，然后结合蒙特卡罗全模拟得到了模拟谱，最后由分析得到的¹³⁷Cs活度的相对误差小于3.0%。这些结果也证实了在高温气冷堆核电站示范工程中使用高纯锗谱仪在线测量燃料球燃耗的可行性。在以上实验和模拟研究的基础上，我们研制了一套可用于高温气冷堆核电站示范工程的燃耗测量系统的原型，包括了高纯锗探测器、准直器、屏蔽体以及刻度源，并实现了石墨球复检和高低富集度燃料球分拣这两个辅助功能，同时还完成了燃耗测量系统与主控系统的接口程序，首次为我国自主研发的新一代核反应堆提供了燃耗测量的解决方案。更多还原

【Abstract】 In a pebble-bed core which employs the multi-pass scheme, it is mandatory to deter-mine the burnup of each pebble after the pebble has been extracted from the core in orderto determine whether its design burnup has been reached or whether it has to be reinsertedinto the core again.The burnup of the fuel pebbles can be determined by measuring the activity of¹³⁷Cswith an HPGe detector because of their good correspondence, which is independent ofthe irradiation history in the core. Compared to HTR-10and other HTGRs, the new chal-lenges in HTR-PM are the rather complex energy spectrum and high background, so thefeasibility study is called for. First, the HPGe spectrometer was set-up for running thedetector at high count rates while keeping the energy resolution adequately high to dis-criminate the¹³⁷Cs peak from other interfering peaks. Based on these settings, the ge-ometrical conditions are also settled. Next, experiments were performed with⁶⁰Co and¹³⁷Cs sources to mimic the counting rates in real applications while optimizing spectraanalysis algorithm and parameters, a precision of2.8%（1σ） can be achieved for the typ-ical high burnup fuel pebbles in the determination of the¹³⁷Cs net counting rate. Then,the relationship between the¹³⁷Cs activity and the net counting rate recorded in the HPGedetector was calibrated with a standard¹³⁷Cs source contained in the center of a graphitesphere with the same dimension as a real fuel pebble. Because the self-attenuation of thecalibration source differs with a fuel pebble, a correction factor of1.07±0.02（p=0.95） tothe calibration was derived by using the efficiency transfer method. Finally, by analyzingthe spectra generated with KORIGEN software followed by detailed Monte Carlo simu-lation, it is predicted that the relative standard deviation of the¹³⁷Cs activity can be stillcontrolled below3.0%despite of the presence of all the interfering peaks. These resultsdemonstrate the feasibility of utilizing HPGe gamma spectrometry in the non-destructiveonline determination of the pebble burnup in HTR-PM.On the foundation of the simulation and experiment research, a full size prototypewhich consists of an HPGe detector, a collimator, a shielding and a calibration sourcewas built. Two miscellaneous functions, reinspection of graphite pebbles and sorting thehigh-enriched and low-enriched fuel elements, were realized. We also implemented andtested the interface routine among the operator, HPGe detector and DCS. In summary, a complete solution for burnup measurement system in HTR-PM is provided.更多还原