Introduction

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“Self-sacrificed Fukushima 50, the final defense.” [1] “Two Tokyo Electric Power Company’s workers exposed 659 mSv at maximum, exceeded dose limits.” [2]“1400 workers are waiting for internal exposure measurement.” [3] “69 workers were out of contact, whose dose was not evaluated.” [4] During the emergency work at the affected plant, Tokyo Electric Power Company and the government experienced various problems in radiation control for emergency workers, such as:

−        Inappropriate exposure monitoring;

−        Mismanagement of dose data;

−        Delayed internal exposure monitoring; and

−        Exceeding dose limits.

“Two workers were contaminated on their feet and transported to a medical institution.” [5] “Radiation exposure was expanded in Seismic Isolation Control Building because the expectations of Tokyo Electric Power Company were not realistic. Internal exposure measurement instruments were defective.” [6] The government faced severe difficulties in radiation exposure reduction for emergency workers, such as:

−        The inappropriate use of respiratory protection;

−        The improper use of protective garments; and

−        Insufficient worker training.

Among the efforts to reduce external exposure, there were problems associated with:

−        The control of working hours;

−        The practical use of a radiation shielding; and

−        The lack of well-prepared work plans.

Based on the experiences and lessons learned, the Ministry of Health, Labour and Welfare (MHLW, hereinafter referred to as “the Ministry”) recognized that adequate measures and systematic preparation for radiation control and exposure reduction should be ensured to manage radiological exposure appropriately should a similar accident occur at another atomic power plant.

“The worker’s death by cardiac infarction was recognized as an occupational disease by so called ‘death from overwork’ or ‘karoshi’.” [7] “A worker was killed in an accident, who was transported to the hospital 63 km away because hospitals nearby were closed.” [8] Regarding medical and health care management for emergency workers, various issues were noted, including:

−        Special medical examinations;

−        On-site triage and initial treatment;

−        Patient transportation;

−        Lodging and food; and

−        Long-term health care for emergency workers.

Regarding lessons learned, the Ministry recognized that the proper management and implementation of medical and health care management in response to a similar accident would require sufficient measures and systematic preparation.

2.    Post-Emergency Response

“The government increased emergency dose limits in the Fukushima Daiich as an exemption.” [9] “Nuclear and Industrial Safety Agency demanded that the Ministry mitigate dose limits by setting a separate dose limit for the Fukushima accident.” [10] On March 14, 2011, the Ministry enforced an ordinance that temporarily increased the radiation exposure dose limit allowed to 250 mSv during the emergency. The paper explains the processes of:

−        Temporarily increasing emergency dose limits;

−        Controlling for the combined emergency and normal exposure doses; and

−        Reducing the limit back to 100 mSv.

“Radiation dose was concealed by dosimeters covered by a lead plate. The Ministry started to investigate the matter as a suspected violation of regulations.” [11] On December 1, 2011, a subcontractor demanded that its contracted workers cover their personal alarm dosimeters with 3-mm thick lead plates to lower dosimeter readings. As a response, the Ministry conducted a fact-finding survey to identify similar cases and devise measures to prevent a recurrence of this incident. The results of the survey provide lessons that can also be applied to transition from emergency radiation protection to normal operation given that the application of emergency dose limits ceased on December 16, 2011 in the affected plant.

“Radiation dose of workers evaluated by Tokyo Electric Power Company and the government might be underestimated, the United Nations’ committee noted.” [12] In April 2013, the Ministry noticed that significant discrepancies were present between the committed effective dose (internal exposure dose) data provided by the Company and data reported by five primary contractors. Based on a re-evaluation of the data, the Ministry required the Company and the five primary contractors to readjust the internal dose data for 479 workers (2.5% of 19,346 emergency workers). Major issues addressed during re-evaluation included:

−        Selection of the intake scenario;

−        Assumptions about the intake date;

−        Assessments of exposure to radiation from short half-life nuclides;

−        Assumptions of undetected 131I exposure due to monitoring delay.

Furthermore, in January 2014, Tokyo Electric Power Company learned that the internal dose for nine emergency workers was assessed using a method other than the standard assessment methods established by the Ministry in a secondary evaluation conducted in July 2013. The Ministry requested that the Company and primary contractors review all internal dose data for 6,245 workers who were engaged in emergency work in March and April 2011 except those previously reviewed. New issues were addressed during the tertiary evaluation.

3.    Decontamination and Remediation Works

“5000 employees of construction industries in Tokyo region had taken seminars for decontamination work in recent two months. Due to a new obligation of receiving an education.” [13] On March 11, 2011, the Japanese government decided to perform decontamination projects around the affected plant. For the radiological protection of the decontamination workers, the Ministry needed to establish new regulations because the existing regulation did not fit into “existing exposure situations” in which radioactive sources were scattered and spread in a wide area around the plant. The new regulations aim to set the appropriate protection standards based on the risk, which is equivalent to or greater than the typical protection required in planned situations. To maintain practicability, the Ministry employed a validated and simplified measurement methodology, considering restrictions in human resources and shortages of supplies in the affected areas.

In April 2012, the Japanese government started dividing the restricted areas into three sub-areas based on the ambient dose rate. By rearranging the restricted area, the government decided to allow resumption of business activities, including manufacturing, farming, hospital operations, welfare facilities, and shops, and related subordinate tasks, such as maintenance, repair, and transportation. In response, the Ministry needed regulations for radiation protection for workers engaged in those activities. The issues that were noted in the deliberation of the regulations were distilled into two points:

−        Whether radiation protection systems established for a planned exposure situation should apply to construction and agricultural work activities in an existing exposure situation; and

−        How to simplify the regulation by the nature of the work activities.

In the summer of 2013, the Ministry of the Environment planned to begin a full-scale process for waste disposal of contaminated soil and wastes removed as part of the decontamination work. The existing regulations were not developed to address such a significant amount of contaminated wastes. Thus, the Ministr had to amend the current regulations for waste disposal workers. The amendment of the general regulation targeted the areas where the existing exposure situation overlapped the planned exposure situation and established the demarcation lines between the two regulations to be applied in each situation.

“‘The government should be responsible for radiation control,’ disconcerted decontamination workers claimed.” [14] “Dose data of decontamination workers were not consolidated. The Ministry of Environment’s request to contractors was unconvincing.” [15] The newly established regulations for radiation protection of decontamination workers obligated employers to monitor, record, and store of workers' dose records and to assess 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, primary contractors of decontamination works decided to establish a central dose registration system. The system started its operation in December 2013 and provided dose distributions in April and July 2015.

4.    Actions for the Future

Results from medical examinations conducted in 2012 of workers who were engaged in radiation work in 2012 as a consequence of the accident showed that the prevalence of abnormal findings was 4.21%, which was 3.23 points increased compared with the 0.98% that was identified prior to the accident in the jurisdiction area of the labor inspection office, which holds jurisdiction over the affected plant. The Ministry concluded that the 2010 and 2012 data cannot be easily compared because 70% of the enterprises within the jurisdiction of the office that reported the 2012 results differed from those that did so in 2010. However, the Ministry decided to implement a comprehensive epidemiological study on the health effects of radiation exposure on all emergency workers. The study team formulated and implemented the pilot study in 2014 and started the full-scale study in April 2015 with funding from a research grant from the Ministry.

   In 2015, the Government of Japan deliberated emergency radiation protection and medical and healthcare systems to ensure preparedness for future nuclear emergencies. When deliberating on emergency dose criteria, the Government of Japan had to harmonize its efforts with international guidance documents and find a way to balance the protection of emergency workers with the prompt implementation of a crisis management plan to maintain control over the nuclear accident. The fact that leading countries have a wide range of emergency dose criteria means that the establishment of emergency dose limits requires social consensus-building. The Ministry succeeded to build a consensus among stakeholders by providing lifetime healthcare systems as compensation for the radiation health risks and by enhancing preparedness to eliminate confusion and disorder and improve the level of protection against health risks. The experience gained shows that acceptance of the health risks due to radiation exposure needs not only a scientific basis, but also social acceptance.

Disclaimer

The information referred to or cited in the papers was not necessarily consistent with the latest information currently available. The cited information was the information used in decision making in those days. For example, dose distribution tables varied in each paper because they were continually revised.

The policy of official information disclosure in the papers conformed to the disclosure policy for interview records of Investigation Committee on the Accident at the Fukushima Nuclear Power Stations. [16] The government of Japan decided to disclose the records with the exception of sections that may disturb the rights and interests of a third party or national security. [17] In the disclosed records, detailed information about the accident, including names of facilities and equipment, was entirely disclosed except the following information:

−        Corporate names of contractors except for the Tokyo Electric Power Company;

−        Names of officers in private companies;

−        Names of governmental officers whose rank was lower than director level. [18]

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

Reference