After the 2011 accident at the Fukushima Daiichi nuclear power plant, nursing-home residents and staff were evacuated voluntarily from damaged areas to avoid radiation exposure. Unfortunately, the evacuation resulted in increased mortalities among nursing home residents. We assessed the risk trade-off between evacuation and radiation for 191 residents and 184 staff at three nursing homes by using the same detriment indicator, namely loss of life expectancy (LLE), under four scenarios, i.e. “rapid evacuation (in accordance with the actual situation; i.e. evacuation on 22 March),” “deliberate evacuation (i.e. evacuation on 20 June),” “20-mSv exposure,” and “100-mSv exposure.” The LLE from evacuation-related mortality among nursing home residents was assessed with survival probability data from nursing homes in the city of Minamisoma and the city of Soma. The LLE from radiation mortality was calculated from the estimated age-specific mortality rates from leukemia and all solid cancers based on the additional effective doses and the survival probabilities. The total LLE of residents due to evacuation-related risks in rapid evacuation was 11,000 persons-d—much higher than the total LLEs of residents and staff due to radiation in the other scenarios (27, 1100, and 5800 persons-d for deliberate evacuation, 20 mSv-exposure, and 100 mSv-exposure, respectively). The latitude for reducing evacuation risks among nursing home residents is surprisingly large. Evacuation regulation and planning should therefore be well balanced with the trade-offs against radiation risks. This is the first quantitative assessment of the risk trade-off between radiation exposure and evacuation after a nuclear power plant accident.

Despite the enormous cost of radiation decontamination, there has been almost no quantitative discussion on how much it would reduce the long-term external radiation exposure in the Evacuation Zone and Planned Evacuation Zone (restricted zone) in Fukushima. The aim of this study is to assess the effectiveness of decontamination and return options and to identify important parameters for estimating the long-term cumulated effective dose (CED) during 15, 30 and 70 year period using data on land-use, population and decontamination in the restricted zone (about 1100 km(2)) in Fukushima. Decontamination of the land is assumed to have a certain efficacy in terms of the reduction of CED. The EeCC (external exposure conversion coefficient) is the parameter having the greatest effect on the percentage of area having CED during the 30 years above 100 m Sv after decontamination, ranging from 13% (EeCC=0.2) to 55% (EeCC=0.6). Therefore, we recommend a detailed investigation of the EeCC in Japan.

To assess the effects of policy measures taken to ensure health and promote well-being, we developed a novel indicator, "loss of happy life expectancy" (LHpLE), under the concept that an objective of life is maximization of lifelong happiness, by using objective survival probabilities and a simple question regarding emotional happiness: "Did you experience a feeling of happiness yesterday [yes/no]?" We measured the emotional happiness of 4990 Japanese respondents through a questionnaire. We then used LHpLE to compare risks after the 2011 Fukushima disaster. LHpLE due to psychological distress was estimated from a decline of emotional happiness, whereas that due to radiation exposure was assessed from shortened life expectancy caused by additional cancer mortality. LHpLE values due to psychological distress in evacuees were approximately 1 to >2 orders of magnitude higher than those due to cancer mortality caused by actual radiation exposure, highlighting the importance of measures to minimize distress following public health emergencies. LHpLE could be used for integrated risk comparison among different types of harms and therefore in government policy-making.

The 2011 Fukushima disaster led to increases in multiple risks (e.g., lifestyle diseases and radiation exposure) and fear among the public. Here, we assessed the additional risks of cancer caused by radiation and diabetes related to the disaster and the cost-effectiveness of countermeasures against these conditions. Our study included residents of the cities of Minamisoma and Soma (10–40 km and 35–50 km north of the Fukushima Daiichi (N° 1) Nuclear Power Station, respectively). We used the loss of life expectancy (LLE) as an indicator to compare risks between radiation exposure and diabetes. We also estimated the cost-effectiveness of radiation-related countermeasures, including restricted food distribution, decontamination, and whole-body counter tests and interventions. Metformin therapy was selected as a representative management for diabetes. The diabetes-related LLEs among residents were 4.1 (95% confidence interval: 1.4–6.8) ×10⁻² years for the whole population and 8.0 (2.7–13.2) ×10⁻² years for 40s to 70s in a scenario that considered the additional incidence of diabetes during the first 10 years. The cancer-related LLEs caused by lifetime exposure to radiation were 0.69 (2.5–97.5 percentile: 0.61–0.79) ×10⁻² years for the whole population and 0.24 (0.20–0.29) ×10⁻² years for 40s to 70s. The diabetes-related LLEs among residents in the above-mentioned scenario were 5.9-fold and 33-fold higher than those attributed to average radiation among the whole population and among the 40s to 70s age groups, respectively. The costs per life-years saved of the radiation countermeasures (i.e., restricted food distribution, decontamination, and whole-body counter tests and interventions) were >1 to >4 orders of magnitude higher than those of general heath checkups and conventional management for diabetes. Our findings indicate that countermeasures to mitigate diabetes are warranted. Policy-makers’ and individuals’ understanding of multiple risks after any disaster will be essential to saving the lives of victims.