Establishment of the central radiation dose registration system for decontamination work involving radioactive fallout emitted by the Fukushima Daiichi APP accident

ABSTRACT

With respect to radiation protection for decontamination efforts involving radioactive fallout emitted by the accident at the Fukushima Daiichi Atomic Power Plant, new regulations were established and obligated employers to monitor, record, and store of workers' dose records, and to check their past dose records at the time of employment. However, cumulative doses may not be properly maintained if a worker declares incorrect values for past doses. In response, with facilitation from the Ministry of Health, Labour and Welfare, primary contractors of decontamination works decided to establish a central dose registration system. There are four major issues in the design of the system to be resolved, included the following: primary contractors (a) do not have a legal responsibility to perform dose control for subcontractors, (b) do not have the right to control decontamination sites, (c) often organize joint ventures, and (d) correspond to a wide range of ambient dose rates. To resolve the issues, requirements of the system included the following: (a) centralize the operation of radiation passbooks, which records past doses and the results of medical examinations to each worker; (b) develop a database system that could register all dose data and accept inquiry from primary contractors; (c) establish a permanent data storage system for transferred records; and (d) provide graded type of services that are appropriate to the risk of radiation exposure. The system started its operation in December 2013 and provided dose distributions in April and July 2015. The average yearly dose in 2014 was 0.7 mSv, which increased by 0.2 mSv from 0.5 mSv in 2012 and 2013. However, no cumulative dose from 2012–2014 exceeded 20 mSv, which was far below than the dose limits (100 mSv/5 years and 50 mSv/year). Although current dose distributions of decontamination workers were within appropriate levels, careful monitoring of dose distribution is necessary for preserving the proper implementation of radiation protection prescribed in the regulations.

KEYWORDS:

• Central dose registration database
• central radiation dose registration and management system
• exposure distribution of decontamination workers
• Fukushima Daiichi APP accident
• radiation protection

Acknowledgments

In acknowledgement of their dedicated contribution, the author expresses sincere appreciation to Masakatsu Kato of Maeda Corporation for dedicated chairmanship of the committee and for being a negotiator with construction industry associations, as well as to Masami Ikai, Kenjiro Miyabe, and Atsuo Ito of the REA for sharing their expertise and for drafting the report, without whom the system could never have been established.

Disclaimer

The findings and conclusions in this report are those of the author and do not necessarily represent the views of the Ministry of Health, Labour and Welfare, Japan.