Citation

Yasui S. J. Occup. Env. Hyg. 2015; 12(6): D96-D102.

Affiliation

Ministry of Health , Labour and Welfare , Tokyo , Japan.

Copyright

(Copyright © 2015, Informa - Taylor and Francis Group)

DOI

10.1080/15459624.2014.992523

PMID

25617063

Abstract

During emergency work at TEPCO Fukushima Daiichi Atomic Power Plant on 1 December 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 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 Ministry of Health, Labour and Welfare (MHLW) extracted a) cases in which a PAD reading was at least 15 % higher than the reading obtained from a radio-photoluminescence dosimeter (RPD), where the dose was greater than 5 mSv in a month (1,813 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 9 primary contractors, including 4 general contractors, 2 plant manufacturers and 3 plant maintenance companies, as the subject 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 16 December 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.

Language: en