Yasui Shojiro
a Ministry of Health, Labor and Welfare , Tokyo , Japan.
J Occup Environ Hyg. 2015;12(6):D96-102. doi: 10.1080/15459624.2014.992523.
During emergency work at TEPCO Fukushima Daiichi Atomic Power Plant on December 1, 2011 a subcontractor demanded that its contracted workers cover their personal alarm dosimeters (PAD) with 3-cm-thick lead plates to lower dosimeter readings. As a response, the Ministry of Health, Labour and Welfare (MHLW) conducted a fact-finding survey to identify similar cases and devise measures to prevent a recurrence of this incident. To screen the suspected cases, the MHLW extracted: a) cases in which a PAD reading was at least 15% higher than the reading obtained from a radio-photolumine-scence dosimeter (RPD), where the dose was greater than 5 mSv in a month (1813 data points), and b) dose data in which PAD readings were less than 50% of the expected dose, where exposure dose may exceed 1 mSv in a day (56 workers, 17,148 data points). From these screenings, the MHLW identified 50 instances from TEPCO and nine primary contractors, including four general contractors, two plant manufacturers, and three plant maintenance companies as the subjects of the due diligence study of exposure data, including interviews. The results of the survey provide lessons that can also be applied to transition from emergency radiation protection to normal operation, as the application of emergency dose limits had ceased on December 16, 2011, in the affected plant. Based on the results of the survey, the MHLW provided administrative guidance documents to TEPCO and 37 primary contractors. The major points of these documents include: a) identification of recorded dose values by comparison of PAD readings to RPD readings, b) storage and management of RPDs and control badges, c) circulation management of PADs and access control to the affected plant, d) estimation of planned doses and setting of alarm values of PADs, e) actions to be taken by contractors if worker dose limits are reached, and f) physical measures to prevent recurrence of the incident.
2011年12月1日，在东京电力公司福岛第一核电站的应急工作期间，一名分包商要求其签约工人用3厘米厚的铅板覆盖个人报警剂量计（PAD），以降低剂量计读数。作为回应，厚生劳动省进行了一次实情调查，以查明类似情况，并制定措施防止此类事件再次发生。为筛查疑似案例，厚生劳动省提取了：a）个人报警剂量计读数比放射光致发光剂量计（RPD）读数至少高15%的案例，且一个月内剂量大于5毫希沃特（1813个数据点）；b）个人报警剂量计读数低于预期剂量50%的剂量数据，且日暴露剂量可能超过1毫希沃特（56名工人，17148个数据点）。通过这些筛查，厚生劳动省确定了东京电力公司和9家主要承包商的50个案例作为暴露数据尽职调查的对象，包括访谈，其中有4家总承包商、2家核电站制造商和3家核电站维修公司。调查结果提供了一些经验教训，这些经验教训也可应用于从应急辐射防护向正常运行的过渡，因为受影响核电站已于2011年12月16日停止适用应急剂量限值。根据调查结果，厚生劳动省向东京电力公司和37家主要承包商提供了行政指导文件。这些文件的要点包括：a）通过比较个人报警剂量计读数和放射光致发光剂量计读数来识别记录的剂量值；b）放射光致发光剂量计和控制徽章的存储与管理；c）个人报警剂量计的流通管理以及进入受影响核电站的权限控制；d）计划剂量的估算和个人报警剂量计报警值的设定；e）如果达到工人剂量限值承包商应采取的行动；f）防止事件再次发生的物理措施。
