Follow-Up of Occupational Health Issues and Measures Taken in Fukushima Daiichi Nuclear Power Plant Where Decommissioning Work Has Continued Over 6 Years Since 2014.

OBJECTIVES: To follow up arising occupational health (OH) issues, measures taken, and their performances in the Fukushima Daiichi Nuclear Power Plant since 2014, and thus share experiences and extend the contribution of OH to long-term decommissioning work and preparation for future disasters. METHODS: Necessary information from official reports and through the OH-related activities involved was collected and analyzed. RESULTS: The issues were categorized into establishment of the OH management system, three individual issues, and others. During the 6 years until end 2019, the OH management system has been strengthened and OH measures have been enriched gradually by visualizing the broader picture, even though some resistance and problems have been encountered. CONCLUSIONS: Improvement in the autonomy of contractors and their ability to respond to environmental changes is necessary.

Assessing the effect of mandatory progress reporting on treatment requirements identified during health examinations at the Fukushima Daiichi Nuclear Power Plant: A time series analysis.

OBJECTIVES: At the Fukushima Daiichi Nuclear Power Plant, run by the Tokyo Electric Power Company, new procedures were introduced as part of the fitness for duty program in July 2016. These were designed to ensure that treatment and further investigations identified as necessary during health examinations were carried out. This study aimed to assess the effectiveness of the initiative by testing whether workers who needed further health examinations obtained them promptly, and whether the number with unmet health needs decreased and the number of workers being treated increased. METHODS: The primary contractors reported aggregated quarterly results of health examinations of both their own and their subcontractors' employees, and follow-up visits to medical institutions were also reported over the next two quarters. The study used data for the period from July 2016 to December 2018. Incident rate ratios were estimated using a multilevel Poisson regression model, including the logarithm of the number of workers who took health examination for each primary contractor company as offset. The linear trend was assessed by treating the number of periods as a continuous variable. RESULTS: The incident rate ratio for workers who needed treatment having a follow-up examination promptly showed a significant decrease over time. The incident rate ratio for those with unmet needs decreased, and those being treated increased over time. CONCLUSIONS: The findings showed that the initiative was effective, with the number of early visits for further health examinations increasing and a decrease in the number of people with unmet health needs.

Continuous improvement of fitness-for-duty management programs for workers engaging in stabilizing and decommissioning work at the Fukushima Daiichi Nuclear Power Plant.

BACKGROUND: Numerous workers have participated in recovery efforts following the accident that occurred at the Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Plant after the Great East Japan Earthquake. These workers, belonging to various companies, have been engaged in various tasks since the accident. Given the hazards and stress involved in these tasks and the relatively long time required to transport sick or injured workers to medical institutions, it became necessary to quickly implement a more stringent management program for fitness for duty than in ordinary work environments. CASE: It took considerable time to introduce and improve a fitness-for-duty program because of several concerns. Various efforts were conducted, sometimes triggered by guidance from the Ministry of Health, Labour and Welfare (MHLW), but the implementation of the program was insufficient. In April 2016, a new program was initiated in which all primary contractors confirmed that their subcontractors had achieved five conditions for workers' fitness for duty on the basis of guidance from the MHLW and occupational health experts. TEPCO confirmed that all primary contractors had implemented the program successfully as of the end of November 2016. CONCLUSION: Following a disaster, even though the parties concerned understand the necessity of fitness-for-duty programs and that companies in high positions have responsibilities beyond their legal requirements, it is highly possible that they may hesitate to introduce such programs without guidance from the government. It is necessary to prepare a governmental framework and professional resources that introduce these stringent management programs quickly.

Prolonged increase in T-cell receptor (TCR) variant fractions of spleen T lymphocytes in pregnant mice after gamma irradiation.

To investigate the relationship between the radiation-induced increase of T-cell receptor (TCR) defective variant fractions and physiological status such as pregnancy, C57BL/ 6N mice were irradiated with 3 Gy of gamma rays at various days of gestation, just before and just after pregnancy. While the highest level of variant fractions in spleen T lymphocytes appeared at 9 days postirradiation and resolved fairly rapidly for nonpregnant mice, the increased variant fractions for pregnant mice irradiated at 16.5 days of gestation reached a plateau at 14 days postirradiation and remained at high levels until 28 days after irradiation. Therefore, variant fractions 28 days postirradiation were measured to determine the overall effect of radiation on the kinetics of TCR variant fractions during gestation. There was no significant difference in the baseline TCR variant fraction between unirradiated nonpregnant and pregnant mice. TCR variant fractions after irradiation were about twofold higher in pregnant mice (from 10.5 days of gestation until delivery) than those in nonpregnant mice. Both gamma radiation and pregnancy caused a decrease in the proportion of naïve T-cell subsets and an increase in TCR variant fractions of naïve T cells. In addition, the prolonged postirradiation increase in the TCR variant fractions of pregnant mice was associated with an increase in serum progesterone level. Differences between pregnant and nonpregnant mice in the kinetics of postirradiation restoration of T-cell systems may be involved in producing the differences in residual TCR variant fractions of these mice.

The delayed manifestation of T-cell receptor (TCR) variants in X-irradiated mice depends on Trp53 status.

The influence of Trp53 on the radiation-induced elevation of T-cell receptor (TCR) variant fractions was examined in splenic T lymphocytes of Trp53-proficient and -deficient mice. Wild-type Trp53+/+, heterozygous Trp53+/- and null Trp53-/- mice were exposed to 3 Gy of X rays at 8 weeks of age. The fraction of TCR-defective variants was measured at various times after irradiation. Initially, the TCR variant fraction increased rapidly and reached its maximum level at 9 days after irradiation before decreasing gradually. In Trp53+/+ and Trp53+/- mice, the TCR variant fraction fell to normal background levels at 16 and 20 weeks of age, respectively. In contrast, the TCR variant fraction of Trp53-/- mice failed to decrease to background levels during the observation period. Baseline levels were then maintained for approximately 60 weeks in the Trp53+/+ mice and approximately 40 weeks in the Trp53+/- mice. After the long flat period, a significant re-increase in the fraction of TCR variants was found after 72 weeks of age in the irradiated Trp53+/+ mice and after 44 weeks of age in the irradiated Trp53+/- mice. Measurement of the fraction of apoptotic cells in the spleen and thymus 4 h after X irradiation at these ages in Trp53+/+ and Trp53+/- mice demonstrated a reduction in apoptosis in the irradiated mice compared to the nonirradiated mice. This suggests that the delayed increase in TCR variants after irradiation is due to a reduction in Trp53-dependent apoptosis.