Whicker J J, Baker G D, Wasiolek P T
Los Alamos National Laboratory, NM 87545, USA.
Health Phys. 2000 Dec;79(6):712-21. doi: 10.1097/00004032-200012000-00018.
Dispersion dynamics of accidentally released radioactive aerosols or gases through laboratory workrooms are determined primarily by airflow, which impacts the level of human exposure and the response of air monitoring instrumentation. Therefore, applying conclusions derived from measurements of the fundamental aspects of airflow (velocity, direction, and turbulence) can lead to better protection of workers by suggesting appropriate locations for air monitoring and sampling. Historically, it has been very difficult to quantitatively measure these fundamental aspects of indoor airflow because of the low flow rates (often <10 cm s(-1)) and difficulties in quantitative measurement of three-dimensional airflow. Recent advances in sonic anemometry have enabled such measurements. For this study, a sonic anemometer was used that was capable of measuring airflow velocities with a sensitivity of about 0.5 cm s(-1) for each of the three-directional components. A sampling frequency of 1 Hz was selected to measure the fluctuations in the air velocity associated with turbulence and expressed in terms of "turbulence intensity." Point measurements of airflow velocities, directions, and turbulence intensities were made at 69 locations in a mechanically ventilated plutonium laboratory located at Los Alamos National Laboratory. Although the measurements were not made with workers present, all measurements were made at a height of 1.5 m, approximately the height of a worker's breathing zone (BZ). Velocities ranged from 8 cm s(-1) to 41 cm s(-1), with a median velocity of 18 cm s(-1). Percent turbulence intensities ranged from 13% to 57% with a median of 34%. The measured velocities and turbulence intensities in the laboratory showed that forced convective flows and turbulent eddy diffusion drive dispersion of released aerosols or gases. Results show that after an airborne release, mixing within the room can take minutes and may not always be complete. This is contrary to simplifying assumptions made by some risk modeling of accidentally released materials in a room. Our results also suggest that the mixing pattern would not be omnidirectional at most release locations, especially in the early stages of the release. Finally, airflow directions were upwards in breathing zones at most workstations. Because most releases in the plutonium laboratory occur at a height immediately below the BZ, the concentrated aerosol could be lifted into the BZ, followed by dispersal to the air monitor with the initiation of alarm.
通过实验室工作室意外释放的放射性气溶胶或气体的扩散动力学主要由气流决定，气流会影响人员暴露水平以及空气监测仪器的响应。因此，应用从气流基本方面（速度、方向和湍流）测量得出的结论，通过建议空气监测和采样的合适位置，可以更好地保护工作人员。从历史上看，由于流速较低（通常<10 cm s⁻¹）以及三维气流定量测量存在困难，定量测量室内气流的这些基本方面一直非常困难。声学风速仪的最新进展使得此类测量成为可能。在本研究中，使用了一种声学风速仪，它能够测量气流速度，对于三个方向分量中的每一个，灵敏度约为0.5 cm s⁻¹。选择1 Hz的采样频率来测量与湍流相关的风速波动，并以“湍流强度”表示。在位于洛斯阿拉莫斯国家实验室的一个机械通风钚实验室的69个位置进行了气流速度、方向和湍流强度的点测量。尽管测量时工作人员不在场，但所有测量均在1.5 m的高度进行，大约是工作人员呼吸区（BZ）的高度。速度范围为8 cm s⁻¹至41 cm s⁻¹，中位速度为18 cm s⁻¹。湍流强度百分比范围为13%至57%，中位数为34%。实验室中测量的速度和湍流强度表明，强制对流和湍流涡扩散驱动了释放的气溶胶或气体的扩散。结果表明，空气传播释放后，室内混合可能需要几分钟，而且可能并不总是完全混合。这与一些关于房间内意外释放物质的风险模型所做的简化假设相反。我们的结果还表明，在大多数释放位置，混合模式并非全向的，尤其是在释放的早期阶段。最后，大多数工作站呼吸区的气流方向是向上的。由于钚实验室中的大多数释放发生在紧接呼吸区下方的高度，浓缩的气溶胶可能会被提升到呼吸区，随后在警报启动时扩散到空气监测器。
