低中水平放射性固体废物活度重建体素优化分析  

Optimization analysis of low and medium level radioactive solid waste activity reconstruction voxels

作　　者：姜学智 顾卫国[1] 单陈瑜 杨桧 王德忠[1] JIANG Xuezhi;GU Weiguo;SHAN Chenyu;YANG Hui;WANG Dezhong(Machinery and Power Engineering College,Shanghai Jiaotong University,Shanghai 200240,China;China Nuclear Power Technology Research Institute Co.,Ltd.,Shenzhen 518000,China)

机构地区：[1]上海交通大学机械与动力工程学院,上海200240 [2]中广核研究院有限公司,深圳518000

出　　处：《核技术》2024年第6期11-18,共8页Nuclear Techniques

摘　　要：传统层析γ扫描方法(Tomography Gamma Scanning,TGS)对废物进行放射性核素活度重建过程中,由于划分大量无效体素导致测量时间长,病态方程迭代求解导致重建精度低。提出了一种体素划分优化方法,其中周向划分基于线源效率积分为环源效率,径向划分则基于不规则划分确定最佳指数权重。通过随机点源活度重建实验,对比了体素划分优化方法和传统体素划分方法的误差情况。针对半径为35 cm的400 L水泥废物桶,在距离废物桶中心74 cm处使用探测效率为40%的同轴HPGe探测器(晶体直径6.09 cm,长度5.18 cm)对^(60)Co和^(137)Cs两种核素进行测量,通过计算不同体素划分方法的条件数和计数率偏差,探究了体素划分方法对重建精度的影响规律。结果显示:传统只加密周向体素的划分方法并不能显著提高重建精度。径向加密方法导致计数率偏差曲线中的极小值点的数量增加和极大值点的数值减小,从而提高重建精度。与传统划分方法相比,体素划分优化方法减少了体素数量,从而测量时间缩短约9/10;同时降低了条件数和计数率偏差,从而将最大重建误差减小约2/3。[Background]During the reconstruction of radionuclide activity of waste by conventional tomography gamma scanning(TGS),the measurement time is long due to the division of a large number of invalid voxels,and the reconstruction accuracy is low due to the iterative solution of the pathology equation.The traditional division method of encrypting only circumferential voxels does not significantly improve the reconstruction accuracy.[Purpose]This study aims to solve the problem of long measurement time and low accuracy of TGS by elaborating the influence law of voxel division method on reconstruction accuracy.[Methods]For a 400 L cement waste drum with a radius of 35 cm,a coaxial HPGe detector with a detection efficiency of 40%(crystal diameter 6.09 cm,length 5.18 cm)was used at a distance of 74 cm from the center of the drum to measure two types of nuclides,^(60)Co and^(137)Cs.The error situation of the optimized method of voxel partitioning and the traditional voxel partitioning method were compared by random point source activity reconstruction experiments.By calculating the condition number and count rate deviation of different voxel partitioning methods,the influence law of voxel partitioning methods on the reconstruction accuracy was investigated.[Results]Comparison results show that the radial encryption method leads to an increase in the number of very small value points and a decrease in the value of very large value points in the count rate deviation curve,which improves the reconstruction accuracy.Compared with the conventional division method,the voxel division optimization method reduces the number of voxels and thus the measurement time by about 9/10;at the same time,it reduces the number of conditions and the count rate deviation,which reduces the maximum reconstruction error by about 2/3.[Conclusion]An optimized voxel division method proposed in this study makes use of the influence law of different voxel divisions on the reconstruction error through theory and experiment,hence improves the measurement

关 键 词：体素划分 条件数 病态方程 测量时间 重建精度 

分 类 号：TL81[核科学技术—核技术及应用]