Marianno C M, Smith M R, Cook K M
Health Phys. 2018 Jan;114(1):13-19. doi: 10.1097/HP.0000000000000725.
This paper will examine deposition patterns of four radionuclides following the Fukushima-Daiichi accident. For nearly 13 d following the event, fission products were released into the environment through planned venting procedures and hydrogen explosions. To assist the government of Japan (GOJ) in the assessment of the releases, the National Nuclear Security Administration's Consequence Management Response Team (CMRT) deployed and took nearly 3 mo of measurements using airborne radiation sensors, fixed monitors, high purity germanium (HPGe) detectors, and health physics survey equipment. From the HPGe detector in-situ results gathered by the CMRT and GOJ teams, the depositions of Cs, Cs, Cs, and I were examined as a function of latitude and longitude. Deposition ratios were calculated to express how each radionuclide was deposited relative to Cs. In addition, the first 30 d of results were compared to the isotopic ratios listed in the Federal Radiological Monitoring and Assessment Center (FRMAC) Dose Assessment Manual Volume 2 Nuclear Power Plant default scenario. This was completed to analyze how the default FRMAC values compared with actual measurements. For Cs:Cs and Cs:Cs (1 wk after shutdown), the ratios were 0.969 ± 0.025 and 0.13 ± 0.007, respectively. These were significantly different from the FRMAC default values of 1.6 and 0.4, but they were of the same order of magnitude. Spatially, larger ratios with high uncertainties were recorded near Tokyo, over 200 km from the accident site. The I to Cs ratios, as expected, decayed exponentially over time but were significantly higher than FRMAC values. Six ratios were greater than 20 within 10 d after shutdown compared to the FRMAC default value of 9.9. In addition, the highest ratios were located less than 75 km to the southwest of the plant. Comparing all the isotopic ratios to the FRMAC manual illustrated differences between the default values and the actual field results. This is at least partly due to the fact that the FRMAC default values are based on an average between a pressurized water reactor and boiling water reactor release. These results of the comparison illustrate that the Assessment Manual default values should only be used when no other data are available.
本文将研究福岛第一核电站事故后四种放射性核素的沉降模式。事故发生后的近13天里，裂变产物通过计划中的排气程序和氢气爆炸释放到环境中。为协助日本政府评估释放情况，美国国家核安全管理局的后果管理响应团队（CMRT）进行了部署，并使用机载辐射传感器、固定监测器、高纯锗（HPGe）探测器和健康物理测量设备进行了近3个月的测量。根据CMRT和日本政府团队收集的HPGe探测器现场结果，研究了铯、铯、铯和碘的沉降与纬度和经度的关系。计算沉降比以表示每种放射性核素相对于铯的沉降情况。此外，将前30天的结果与联邦放射监测与评估中心（FRMAC）剂量评估手册第2卷核电站默认情景中列出的同位素比率进行了比较。这样做是为了分析FRMAC默认值与实际测量值的差异。对于铯:铯和铯:铯（停机1周后），比率分别为0.969±0.025和0.13±0.007。这些值与FRMAC默认值1.6和0.4有显著差异，但处于同一数量级。在空间上，在距离事故现场200多公里的东京附近记录到了具有高不确定性的较大比率。正如预期的那样，碘与铯的比率随时间呈指数衰减，但明显高于FRMAC值。与FRMAC默认值9.9相比，停机后10天内有六个比率大于20。此外，最高比率出现在核电站西南不到75公里处。将所有同位素比率与FRMAC手册进行比较，说明了默认值与实际现场结果之间的差异。这至少部分是由于FRMAC默认值是基于压水反应堆和沸水反应堆释放的平均值。比较结果表明，只有在没有其他数据可用时，才应使用评估手册的默认值。
