核废物桶放射性检测的螺旋γ扫描技术

Helical gamma scanning technique for activity detection of radioactive waste drum

螺旋γ扫描(Helical Gamma Scanning,HGS)技术在分段γ扫描(Segmented Gamma Scanning,SGS)技术的基础上,改进了扫描方式和重建算法,实现了连续扫描测量。针对三种放射性核素在不同密度介质的400 L废物桶中的情况,采用蒙特卡罗方法验证了HGS技术的准确性。结果显示:低密度时,SGS的均方根误差超过8%,而HGS的均方根误差控制在6.5%以内;中密度时,SGS的重建误差均偏小55%以上,严重低估废物桶的放射性危险,而HGS可以有效检测到位于废物桶两端的放射性核素。相比于SGS的测量时间,HGS至少可以节约一半。整体而言,HGS技术适用于低中密度400 L废物桶的放射性检测,且测量时间优于SGS技术和层析γ扫描(Tomographic Gamma Scanning,TGS)技术,测量精度优于SGS技术。

[Background]Non-destructive assay(NDA)is a widely used method to assay the amount and categories of radioactive nuclides within the waste drum,segmented gamma scanning(SGS)is a normal method.[Purpose]This study aims to evaluate the performance of helical gamma scanning(HGS)for 400-liter waste drum.[Methods]Based on SGS,a new HGS detection method was proposed.The scanning mode and reconstruction algorithm were improved in SGS to realize continuous scanning measurement.Monte-Carlo method was employed to simulate the reconstruction process of three nuclides in a 400-liter waste drum filled with three different density media.Results of three point sources and three homogeneous medium materials were compared.[Results]At low density,the root mean square error of SGS is more than 8%,while that of HGS is less than 6.5%.At medium density,the reconstruction error of SGS is more than-55%,which seriously underestimates the risk of waste drum.Compared with SGS,HGS saves at least half of the measurement time.[Conclusions]HGS technology is suitable for measuring 400-liter waste drum whose density is low and medium.The measurement time of HGS is less than SGS and tomographic gamma scanning(TGS).The measurement accuracy of HGS is better than SGS.