在核燃料制造中,吸入铀气溶胶可能是一个问题。ICRP提供了各种铀化合物的默认吸收参数,但也建议确定特定材料的吸收参数,以改善暴露于空气放射性的个人的剂量计算。气溶胶颗粒大小以两种潜在的重要方式影响内部剂量测定计算:呼吸道各个区域的颗粒沉积效率取决于空气动力学颗粒大小,沉积材料的溶解速率可以根据颗粒大小而变化,形状,和孔隙率,因为较小的颗粒倾向于具有比较大的颗粒更高的表面体积比。然而,ICRP模型假设给定材料的沉积颗粒以相同的速率溶解,无论大小如何,并且吸收血液中的溶解物质通常在肺的所有部分瞬间发生(除了鼻区的前部,其中假定为零吸收)。在目前的工作中,对于在工厂收集的铀气溶胶,研究了颗粒大小对模拟肺液中溶解的影响,并评估了其对内部剂量测定计算的影响。使用便携式级联冲击器在核燃料制造厂对尺寸分馏的铀气溶胶进行了采样。吸收参数,根据ICRP人类呼吸道模型描述材料的溶解,使用模拟肺液在体外测定不同大小的分数。在100天的时间内在16个时间点收集样品。使用电感耦合等离子体质谱法和α光谱法测定样品的铀含量。此外,进行了补充实验,以研究pH值漂移和铀吸附对过滤器支架的影响,因为它们可能会影响得出的吸收参数。在工厂的四个主要车间,观察到未溶解的分数随时间的变化而变化。对于小的切点,较大部分的颗粒活性倾向于溶解,但有例外。吸收参数(快速分数,快速速度,和慢速),随着时间的推移,从未溶解的部分中得出,总体上与ICRP关于铀化合物的默认建议完全一致。在工厂的四个主要车间中注意到吸收参数的差异(即,其中气溶胶特性预计会有所不同)。造粒车间与最不溶性材料相关,转化车间与最可溶性材料相关。得出的肺吸收参数与空气动力学粒径(撞击器阶段切点)之间的相关性较弱。例如,来自低(<5μm)和大(≥5μm)切割点的撞击阶段的平均吸收参数没有显着差异。pH值的漂移和过滤器支架上的吸附似乎是次要的,但是发现可能会发生颗粒泄漏。观察到不溶解的分数和一定程度的肺吸收参数根据所研究的空气动力学尺寸分数而变化。表明大小分馏(例如,在进行体外溶出率实验之前,使用级联冲击器)是合适的。0.01-0.02μm和1-2μm的尺寸范围是特别感兴趣的,因为它们对应于人呼吸道模型(HRTM)中的肺泡沉积最大值。在目前的工作中,然而,对空气动力学大小的依赖性似乎不太重要,但不能排除粒子反弹掩盖了撞击后期的结果。此外,值得注意的是,模拟肺液样本收集的时间(在我们的情况下为100d)影响用于确定肺吸收参数的曲线拟合程序,特别是如果考虑更少的样品,则会增加缓慢的速率。
Inhalation exposure to
uranium aerosols can be a concern in nuclear fuel fabrication. The ICRP provides default absorption parameters for various
uranium compounds but also recommends determination of material-specific absorption parameters to improve dose calculations for individuals exposed to airborne radioactivity. Aerosol particle size influences internal dosimetry calculations in two potentially significant ways: the efficiency of particle deposition in the various regions of the respiratory tract is dependent on aerodynamic particle size, and the dissolution rate of deposited materials can vary according to particle size, shape, and porosity because smaller particles tend to have higher surface-to-volume ratios than larger particles. However, the ICRP model assumes that deposited particles of a given material dissolve at the same rate regardless of size and that uptake to blood of dissolved material normally occurs instantaneously in all parts of the lung (except the anterior portion of the nasal region, where zero absorption is assumed). In the present work, the effect of particle size on dissolution in simulated lung fluid was studied for uranium aerosols collected at the plant, and its influence on internal dosimetry calculations was evaluated. Size fractionated uranium aerosols were sampled at a nuclear fuel fabrication plant using portable cascade impactors. Absorption parameters, describing dissolution of material according to the ICRP Human Respiratory Tract Model, were determined in vitro for different size fractions using simulated lung fluid. Samples were collected at 16 time-points over a 100-d period.
Uranium content of samples was determined using inductively coupled plasma mass spectrometry and alpha spectrometry. In addition, supplementary experiments to study the effect of pH drift and
uranium adsorption on filter holders were conducted as they could potentially influence the derived absorption parameters. The undissolved fraction over time was observed to vary with impaction stage cut-point at the four main workshops at the plant. A larger fraction of the particle activity tended to dissolve for small cut-points, but exceptions were noted. Absorption parameters (rapid fraction, rapid rate, and slow rate), derived from the undissolved fraction over time, were generally in fair agreement with the ICRP default recommendations for uranium compounds. Differences in absorption parameters were noted across the four main workshops at the plant (i.e., where the aerosol characteristics are expected to vary). The pelletizing workshop was associated with the most insoluble material and the conversion workshop with the most soluble material. The correlation between derived lung absorption parameters and aerodynamic particle size (impactor stage cut-point) was weak. For example, the mean absorption parameters derived from impaction stages with low (taken to be <5 μm) and large (≥5 μm) cut-points did not differ significantly. Drift of pH and adsorption on filter holders appeared to be of secondary importance, but it was found that particle leakage can occur. Undissolved fractions and to some degree derived lung absorption parameters were observed to vary depending on the aerodynamic size fraction studied, suggesting that size fractionation (e.g., using cascade impactors) is appropriate prior to conducting in vitro dissolution rate experiments. The 0.01-0.02 μm and 1-2 μm size ranges are of particular interest as they correspond to alveolar deposition maxima in the Human Respiratory Tract Model (HRTM). In the present work, however, the dependency on aerodynamic size appeared to be of minor importance, but it cannot be ruled out that particle bounce obscured the results for late impaction stages. In addition, it was noted that the time over which simulated lung fluid samples are collected (100 d in our
case) influences the curve-fitting procedure used to determine the lung absorption parameters, in particular the slow rate that increased if fewer samples were considered.