In Japan, active provision of information about nuclear prevention measures and PDSI to residents who live around a nuclear power plant has begun based on the experience of the FDNPS accident in 2011 [17]. The present study identified the characteristics of the guardians living 5–30 km (UPZ) from a nuclear power plant who wished to receive PDSI (Group 1) or did not wish to receive PDSI (Group 2) and their awareness of nuclear prevention measures including prophylactic SI for pregnant woman and their young children living near the GNPP. The results showed that about 40% of the guardians had not known about SI, and about 60% of the guardians had not known of a public shelter near their house to evacuate to during a nuclear power plant emergency. This study showed that the guardians who lived 5–30 km from a nuclear power plant were not familiar with SI and nuclear prevention measures.
In Japan, when an emergency occurs at a nuclear power plant, all PAZ residents should take prophylactic SI and then begin evacuation before release of radionuclides into the atmosphere. On the other hand, UPZ residents should first shelter in their house or a public shelter, and then begin evacuation depending on the status of the nuclear plant accident and the air dose rate in their residential area [10].
Therefore, the recommendation of the World Health Organization (WHO) for a nuclear emergency is that, in areas further away from a nuclear power plant emergency situation, PDSI to households is not considered feasible, and stocks of SI should be stored strategically at, for example, schools, hospitals, pharmacies, fire stations, police stations, and civil defense centers such as public shelters [18].
However, the present study showed that of 40% guardians thought that sheltering is not useful for reducing the radiation exposure dose. Sheltering with closed windows and any forced ventilation shut off is not completely effective for avoiding radiation exposure, though sheltering is a relatively simple protective measure to reduce internal and external radiation exposure from various radionuclides including radioactive iodine in the early phase of a nuclear accident [19]. In a study, the Japanese government showed that, compared to staying outdoors, sheltering in a standard wooden house can reduce external radiation exposure by about 60%. In addition, a standard rebar house can reduce external radiation exposure by about 90% compared to staying outdoors. Furthermore, internal exposure can be reduced by about 30% compared to staying outdoors, regardless of the type of house materials without ventilation [20]. In the case of a nuclear emergency, stand-alone protective action, such as only prophylactic SI, should not be considered. It is important to give residents a strong message about the effectiveness of sheltering and recommend that they prepare to stay in their house in the case of a nuclear disaster [19].
In the present study, 83% of guardians wished to receive PDSI, and 84.6% wished to receive prophylactic SI for their children in a nuclear emergency. However, of the guardians who wished to receive PDSI, 31.9% did not know about SI before the study, and 63.7% felt anxious about prophylactic SI for their children. Similarly, of the guardians who wished to receive prophylactic SI for their children, 37.4% did not know about SI before the study, and 67.2% felt anxious about prophylactic SI for their children. These results show conflict between the guardian’s awareness of SI, in other words, they wished to receive PDSI and also wished to receive prophylactic SI for their children during a nuclear emergency, but many of them felt anxious about prophylactic SI for their children.
The groups most likely to benefit from ITB are children, adolescents, and pregnant and breastfeeding women [21, 22], so priority should be given to children and younger adults. Side effects of SI are rare and include iodine-induced transient hyperthyroidism or hypothyroidism and allergic reactions [22, 23]. However, pregnant women and guardians of young children tend to be cautious about drugs in general, not only prophylactic SI [11]. The result of the regression analysis showed an independent association between guardians who wished to receive PDSI and those who thought that pregnant women should be given prophylactic SI in a nuclear emergency (OR = 6.57). It is important to inform pregnant women and guardians of young children about the risks associated with prophylactic SI, including the benefits and side effects.
The present study showed that 33.7% of the guardians thought that SI could prevent exposure from all radionuclides. Prophylactic SI can block or reduce the accumulation only of radioactive iodine in the thyroid [19]. Prophylactic SI within one to two hours before inhalation of and exposure to I-131 can block > 90% of thyroid uptake of I-131 [24]. Therefore, prophylactic SI is most effective in the first few hours of internal exposure. Nevertheless, there is a popular misconception that SI is a silver bullet against harm from radiation exposure. The WHO recommended training of health professionals and emergency workers in risk communication to raise public awareness (e.g., provision of leaflets, organizing campaigns) [18]. All local municipalities in which NPPs are located have a responsibility to perform nuclear prevention measures such as providing shelter, disseminating information concerning SI/ITB, and performing evacuation drills several times a year in preparation for the possibility of a nuclear emergency. However, the results of this study showed that limited numbers of people (18.3%) have participated in a nuclear emergency drill, possibly because of the low number of health communication professionals, a lack of opportunity to participate in such a drill, and low awareness of disaster prevention measures among local residents [17, 25, 26]. Education is key to disaster prevention, preparation, response, and recovery [27]. Our previous study revealed that 89.8% (467/520) of mothers residing near the Sendai Nuclear Power Plant of Kagoshima Prefecture, Kyusyu, Japan expressed anxiety regarding prophylactic SI for their children; this anxiety was positively correlated with their wish to consult an expert about SI and negatively correlated with having confidence about prophylactic SI for their children [28]. To maintain and enhance nuclear prevention measures including prophylactic SI for residents living 5–30 km from a nuclear power plant, it is essential to educate specialists who work in the field of health about countermeasures in the case of a nuclear accident in the local area.
There are several limitations in the study, First, the study was conducted only in the UPZ of the GNPP in Japan, one of the areas where PDSI was started to UPZ residents under 40 years of age in 2019 [13]. Since PDSI was not started in all UPZ areas in Japan, the study’s results are not representative of the awareness of all UPZ residents. However, as soon as the PDSI system is ready, there will be pre-distribution spread over a wide area of the UPZ as well, and the present study might be considered as pioneering data regarding PAZ guardians of young children. Second, in our study of the UPZ area we did not collect data regarding the reasons for the guardians’ anxiety about prophylactic SI for their children. Furthermore, we also did not collect data regarding the guardians’ experiences or involvement in any disasters, including the FDNPS accident. These perceptions about SI and previous experience (or not) with disaster may have influenced the guardians’ awareness of nuclear emergency measures. Lastly, this study included only residents who answered “within 30 km [UPZ]” from the GNPP. However, it is not clear that all guardians know the precise distance from their house to the GNPP. All data were collected from the kindergartens located within 30 km from the GNPP. Therefore, if a nuclear accident occurred in the GNPP, the study participants, the guardians or kindergarten staff should take the appropriate nuclear prevention measures to reduce radiation exposure. Thus, this study might provide effective baseline data for preparing preventive measures for nuclear disasters.