The difficulty of nuclear emergency prevention measures during natural disasters: ongoing challenges in Japan

It is crucial to anticipate nuclear emergency scenarios and implement effective measures. Japan’s climate and topography make it vulnerable to natural disasters; thus, it is necessary to address compounding and cascading disaster scenarios involving the simultaneous occurrence of natural and nuclear disasters. On 1 January 2024, an earthquake hit the Noto region of Ishikawa Prefecture, resulting in damage to the area around the Shika Nuclear Power Plant, located 90 km from the epicenter. This earthquake revealed that, in the event of a complex disaster, it is possible that residents living within 30 km of the Shika Nuclear Power Plant will be completely unprepared for a nuclear disaster. In the event of a complex disaster, it is crucial to implement appropriate countermeasures while balancing responses to both nuclear and natural disasters and optimizing radiation disaster prevention measures.


Opinion article
In 2024, global nuclear power generation and escalating conflicts leading to the potential use of nuclear weapons are heightening the risk of nuclear emergencies [1][2][3].Factors contributing to such emergencies encompass various intentional or accidental scenarios.During radiological or nuclear emergencies, the risk of material spills or releases demands swift action to prevent public exposure.Thus, it is crucial to anticipate nuclear emergency scenarios and implement effective countermeasures.
Japan's Basic Plan for Nuclear Emergency Preparedness adheres to the Radiation Emergency Mitigation Framework, established by the International Atomic Energy Agency (IAEA).The IAEA delineates two critical zones in the event of a nuclear power plant accident: (i) the Precautionary Action Zone (PAZ) with a 5 km radius, requiring immediate evacuation, and (ii) the Urgent Protective Action Planning Zone (UPZ) with a 30 km radius, where indoor sheltering in airtight buildings is necessary [4].Japan has established both PAZ and UPZ, and radiation protection facilities are constructed in both zones.The facility is airtight, and the building is equipped with a positive pressure system to prevent the intake of radioactive materials and a ventilation system that can remove radioactive materials.Additionally, essential supplies such as water, food, and other necessities are stockpiled within the facilities, enabling safe indoor sheltering while reducing the risk of exposure.As Japan's climate and topography make it vulnerable to natural disasters, there is need to address compounding and cascading disaster scenarios involving the simultaneous occurrence of natural and nuclear disasters [5].Notably, on 11 March 2011, the Great East Japan Earthquake was a compound disaster of a magnitude 9.0 earthquake and a devastating tsunami, culminating in the Fukushima Daiichi Nuclear Power Plant accident [6].This incident featured substantial health ramifications, particularly among vulnerable demographics such as older people and people with health conditions, attributable to inadequately prepared evacuation procedures [7][8][9][10][11].Consequently, significant revisions have been incorporated into the Nuclear Regulation Authority Guide for Emergency Preparedness and Response, prioritising human life in compound disaster scenarios involving both nuclear and natural disasters [12].Specifically, if the direct threat to human life from a natural disaster is exceedingly high, evacuation protocols for the natural disaster take precedence, with measures against nuclear accidents/disasters implemented once safety from natural disasters is ensured.Although Japan's nuclear emergency preparedness guidelines are based on the IAEA's safety standards, their applicability to Japan's intricate disaster landscape, encompassing earthquakes and tsunamis, remains unclear [13].
On 1 January 2024, a magnitude 7.6 earthquake struck the Noto region of Ishikawa Prefecture, originating from the Noto Peninsula.Located approximately 90 km from the epicentre, in Shika Town, where a maximum seismic intensity of 7 was recorded, issues were found during the inspection of reactor 1 at the Hokuriku Electric Power Shika Nuclear Power Plant.Specifically, a component designed to support the control rod drive mechanism was dislodged.Additionally, an oil slick was detected surrounding the transformer of reactor 2. However, there was no confirmation of damage to the reactor itself, such as total loss of power or loss of coolant, nor any readings indicating radiation levels exceeding regulatory limits for radiation exposure [14].The impact of the earthquake on the surrounding areas was significant.As of 8 May 2024, 245 people had reportedly died in the Noto region, including Wajima City.Building collapses were notable [15].From 4 January to 21, a rapid hazard assessment survey conducted in 11 cities and towns in Ishikawa Prefecture revealed that of the 31 600 structures surveyed, approximately 40% or 12 615 structures were deemed inaccessible owing to the risk of collapse.In Shika Town, where the Shika Nuclear Power Plant is located, 2318 buildings were reported to be completely or partially destroyed [16].The damage extended beyond residential areas, impacting crucial elements of nuclear emergency preparedness such as designated evacuation routes and radiation protection facilities, leading to the isolation of certain areas.On 12 April 2024, the Nuclear Emergency Prevention Subcommittee of Japan's Cabinet Office released documents showing that 7 of the 11 major national and prefectural roads designated as evacuation routes within the UPZ around the Shika Nuclear Power Plant in Ishikawa Prefecture were either cracked, damaged, or closed.Some roads designated as evacuation routes remained closed with no alternative routes available; the closures were lifted approximately 15 d after the disaster had occurred [17].Accordingly, 14 isolated areas emerged within the UPZ.Although most isolated areas were resolved through road clearance operations, some required helicopter evacuation to alleviate isolation.Among the 14 isolated areas, 3 had more than 20 individuals.Rescue operations in these areas occurred 12 d after the earthquake, with groups of 20, 26, and 61 individuals rescued.One individual remained isolated for 16 d.There are 21 radiation protection facilities located around the Shika Nuclear Power Plant.However, because of building damage (one case), flooding caused by sprinkler activation (two cases), and damage to buildings outside the designated protection areas on the same premises (one case), access to protection zones became restricted in 4 out of the 21 facilities.Additionally, even in facilities where access was possible, two buildings had nonfunctional positive pressure systems, rendering them unusable as radiation protection facilities [17].
In a compound disaster involving both natural and nuclear disasters, striking a balance in addressing the response to both events can be challenging because the proportion of damage caused by natural calamities and nuclear disasters varies depending on the specific case.
The 2024 Noto Peninsula Earthquake can be assumed to be a case wherein damage caused by natural disasters surpassed that caused by the nuclear incident.This earthquake showed that residents living within the UPZ would be unable to take any safety measures against nuclear emergencies during compound disaster situations in the foreseeable future, attributable to circumstances such as road closures of evacuation routes within the UPZ, citizens' inability to use radiation protection facilities, or isolation lasting for two weeks.In its emergency preparedness guidelines, the Japanese government prioritises evacuation actions for compound natural disasters, particularly in cases where direct risk to human life from natural disasters is extremely high.In response to the Noto earthquake, the Nuclear Regulation Authority, which is reviewing guidelines for indoor evacuation procedures, has concluded that significant changes to amend these guidelines are not necessary.They have, however, not addressed some of the highlighted issues, such as the need for residents' self-help measures from a nuclear fallout or seismic reinforcement of a facility.While it is essential to prioritise risk reduction in natural disasters, it is undesirable to have a situation where there is no provision for radiation disaster preparedness.Therefore, it is imperative to empower residents living around nuclear power plants to protect themselves through measures such as the pre-distribution of stable iodine tablets and thorough radiation disaster education [18,19].Additional emergency preparedness measures should be adopted at both individual and municipal level, especially in areas where the geographical risk of being at a disadvantage during evacuation operations, compared to other areas, is known in advance.
Achieving a balance in response measures becomes more challenging when the impacts of nuclear and natural disasters occur at similar levels.Moreover, it is critical to optimise radiation emergency preparedness while considering the balance of disaster responses during compound disasters.The Fukushima Daiichi nuclear disaster is as an example of excessive response to nuclear accidents owing to a disproportionate emphasis on the impact of radiation, leading to an imbalance in disaster response.As a result, there were numerous disaster-related deaths which are not attributable to the direct impact of the disaster but rather to the physical and mental strain of evacuation [20][21][22][23].The accident also underscores the need to optimize radiation protection measures and reduce the risk of secondary health effects.During compound disasters, excessive emphasis on either aspect of mitigation could potentially exacerbate health implications.To minimise discussion on disaster countermeasures, the Japanese government believes that the balance of disaster response should not be a point of discussion.However, as each disaster differs in scale and damage, disaster response should be flexible and balanced.
In the recent Noto earthquake, concerns have been raised regarding the seismic resilience of radiation protection facilities, functionality of the positive pressure machines used, and the durability of roads utilised as evacuation routes.In response, the Nuclear Regulation Authority convened to evaluate if the current guidelines and response measures for nuclear emergencies are indeed optimal, based on data from this earthquake and evacuation plans.It is imperative to meticulously discuss and reassess the balance of support during compound disasters, reconsider the evacuation guidelines to mitigate secondary health risks, and optimise radiation protection measures.