Poudel Deepesh, Avtandilashvili Maia, Bertelli Luiz, Klumpp John A, Tolmachev Sergei Y
Radiation Protection Division, Los Alamos National Laboratory, Los Alamos, NM.
US Transuranium and Uranium Registries, Washington State University, Richland, WA.
Health Phys. 2021 Mar 1;120(3):258-270. doi: 10.1097/HP.0000000000001311.
Inhalation of plutonium is a significant contributor of occupational doses in plutonium production, nuclear fuel reprocessing, and cleanup operations. Accurate assessment of the residence time of plutonium in the lungs is important to properly characterize dose and, consequently, the risk from inhalation of plutonium aerosols. This paper discusses the long-term retention of plutonium in different parts of the respiratory tract of two workers who donated their bodies to the US Transuranium and Uranium Registries. The post-mortem tissue radiochemical analysis results, along with the urine bioassay data, were interpreted using Markov Chain Monte Carlo and the latest biokinetic models presented in the Occupational Intakes of Radionuclides series of ICRP publications. The materials inhaled by both workers were found to have solubility between that of plutonium nitrates and oxides. The long-term solubility was also confirmed by comparison of the activity concentration in the lungs and the thoracic lymph nodes. The data from the two individuals can be explained by assuming a bound fraction (fraction of plutonium deposited in the respiratory tract that becomes bound to lung tissue after dissolution) of 1% and 4%, respectively, without having to significantly alter the particle clearance parameters. Effects of different assumptions about the bound fraction on radiation doses to different target regions was also investigated. For inhalation of soluble materials, an assumption of fb of 1%, compared to the ICRP default of 0.2%, increases the dose to the most sensitive target region of the respiratory tract by 258% and that to the total lung by 116%. Some possible alternate methods of explaining higher-than-expected long-term retention of plutonium in the upper respiratory tract of these individuals-such as physical sequestration of material into the scar tissues and possible uptake by lungs-are also briefly discussed.
在钚生产、核燃料后处理及清理作业中，吸入钚是职业剂量的一个重要来源。准确评估钚在肺部的滞留时间对于正确描述剂量以及吸入钚气溶胶所致风险至关重要。本文讨论了两名将遗体捐赠给美国超铀和铀登记处的工人呼吸道不同部位钚的长期滞留情况。利用马尔可夫链蒙特卡罗方法以及国际放射防护委员会（ICRP）出版物《放射性核素职业摄入量》系列中最新的生物动力学模型，对尸检组织放射化学分析结果以及尿液生物测定数据进行了解释。发现两名工人吸入的物质其溶解度介于硝酸钚和氧化钚之间。通过比较肺部和胸段淋巴结中的活度浓度，也证实了长期溶解度情况。在不必显著改变颗粒清除参数的情况下，分别假设结合分数（呼吸道中沉积的钚在溶解后与肺组织结合的分数）为1%和4%，就可以解释这两人的数据。还研究了关于结合分数的不同假设对不同靶区辐射剂量的影响。对于吸入可溶性物质，与ICRP默认的0.2%相比，假设结合分数为1%会使呼吸道最敏感靶区所受剂量增加258%，使全肺所受剂量增加116%。本文还简要讨论了一些可能用于解释这些个体上呼吸道中钚长期滞留高于预期的其他方法，例如物质在瘢痕组织中的物理隔离以及肺部可能的摄取情况。
