Environment Regeneration Office, Fukushima Revitalization Headquarters, Tokyo Electric Power Company Holdings Inc, Fukushima, Japan.
J Radiol Prot. 2023 Jan 25;43(1). doi: 10.1088/1361-6498/acab0c.
Since the Fukushima Daiichi Nuclear Power Station accident, evacuation orders have been lifted except for the difficult-to-return zones (DRZs). Within the DRZs, there has been designated a special zone for reconstruction and revitalisation (SZRR). Decontamination of the SZRR has been promoted so that evacuation orders may be lifted. Previous studies measured individual external doses in the evacuation order-lifted zones (ELZs) and other living areas where the annual additional individual external dose was overall less than approximately 5 mSv y. However, there have been few reports about the measurement of individual external doses in a SZRR or outside of an SZRR (O-SZRR). In SZRRs and O-SZRRs, Tokyo Electric Power Company Holdings employees work mainly outdoors. Therefore, the employees' individual external doses and air dose rates were measured in these zones from March 2020 through January 2021. Our key results were:The median (minimum to maximum) individual external doses at outdoor locations were 0.16Sv h(0.05-0.63Sv h), 0.57Sv h(0.15-3.92Sv h), and 1.36Sv h(0.14-11.91Sv h) for the ELZ, SZRR, and O-SZRR, respectively.The conversion coefficients for the air dose rate measured by airborne monitoring to individual external dose were 0.23, 0.38, and 0.50 for the ELZ, SZRR, and O-SZRR, respectively. The conversion coefficients were below 0.6, which was used in the national government model for estimating external exposure dose from air dose rate. In addition, the conversion coefficients for the SZRR and O-SZRR in air dose rates of less than 1.5Sv hdiffered from those obtained for the entire measurement range of this study.The conversion coefficient from air dose rate at a height of 1 m above ground level to individual external dose was researched across a broader and higher range of air dose rates than in the previous study (0.24-20.89Sv h). The conversion coefficient is confirmed to be 0.7, similar to previous studies.
自福岛第一核电站事故以来，除了难以返回区 (DRZ) 外，已解除了撤离令。在 DRZ 内，指定了一个特别重建和振兴区 (SZRR)。为解除撤离令，推进了 SZRR 的去污工作。先前的研究测量了撤离令解除区 (ELZ) 和其他生活区域的个人外照射剂量，这些区域的年个人外照射剂量总体上低于约 5 mSv y。然而，关于 SZRR 或 SZRR 之外 (O-SZRR) 的个人外照射剂量的测量报告较少。在 SZRR 和 O-SZRR 中，东京电力公司控股员工主要在户外工作。因此，从 2020 年 3 月到 2021 年 1 月，在这些区域测量了员工的个人外照射剂量和空气剂量率。我们的主要结果是：户外场所的个人外照射剂量中位数（最小值至最大值）分别为 0.16Sv h（0.05-0.63Sv h）、0.57Sv h（0.15-3.92Sv h）和 1.36Sv h（0.14-11.91Sv h），分别为 ELZ、SZRR 和 O-SZRR；通过机载监测测量的空气剂量率转换为个人外照射剂量的转换系数分别为 0.23、0.38 和 0.50，分别为 ELZ、SZRR 和 O-SZRR；转换系数低于 0.6，这是国家政府用于估算空气剂量率引起的外照射剂量的模型中使用的值。此外，空气剂量率小于 1.5Sv h 的 SZRR 和 O-SZRR 的转换系数与本研究整个测量范围内获得的值不同；地面以上 1 米高度的空气剂量率与个人外照射剂量的转换系数的研究范围比以前的研究更广、更高（0.24-20.89Sv h）。转换系数被确认为 0.7，与之前的研究相似。
