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Abstract
The Fukushima Daiichi disaster occurred in March 2011 in Lkuma and Futaba Prefectures. The Fukushima Daiichi Nuclear Power Plant consisted of six boiling water reactors, which generated the electric power of 4.5 GWe. The disaster occurred after the energy accident, which was caused by a tsunami and the TMhoku earthquake. According to Tokyo Electrical Power Company, the Tohoku-Chihou-Taiheiyou-Oki Earthquake happened on Friday, March 11, 2011, at 2:46 p.m; the magnitude of the earthquake was 9.0, with the intensity of 6 in Fukushima Prefecture (TEPCO 2018). Also, the earthquake was the fourth-strongest earthquake in the world. The tsunami at Fukushima Prefecture reached 14 meters in height and 150 meters in depth, according to TEPCO (2018) report. The findings provided by World Health Organization (WHO) showed that because of the TMhoku earthquake and tsunami, the Fukushima Daiichi Nuclear Power station was unable to sustain in cooling capacity, which led to a disaster rated 7 by the International Nuclear Events Scale (INES). The casualties of the accident included 15 891 deaths, 2579 missing people, and large quantities of radioactive materials released in the environment on 12 March 2011 (World Health Organization 2015).
Description of the Industry
The history of reactors in Japan started in the 1950s when the government initiated a nuclear research program in 1954. Japan held a budget of 230 million Yen for investing in nuclear energy production. In 1955, the Energy Basic law permitted the use of nuclear technology only for peaceful purposes; the law was established based on three main points democratic methods, independent management, and transparency, which created the basis of the nuclear research activities as well as cooperation with international agencies (World Nuclear Association 2017, para. 12). In 1956, Japan Atomic Energy Commission (JAEC) was launched along with several nuclear energy-related bodies such as the Nuclear Safety Commission (NSC), the Science & Technology Agency, Japan Atomic Energy Research Institute (JAERI) (World Nuclear Association 2017).
The first nuclear reactor was a boiling water reactor prototype that produced electricity. The reactor was called Japan Power Demonstration Reactor (JPDR) and was in service from 1963 to 1976. However, the first commercialized nuclear power reactor was imported from the UK; it was Tokai 1, a 160 MWe gas-cooled reactor (Magnox), which operated from 1966 till 1998. Later, light water reactors (LWRs) utilizing enriched uranium, boiling water reactors (BWRs), and pressurized water reactors (PWRs) have been constructed and commercially operated. By the end of the 1970s, the nuclear power industry of Japan had developed its own internal nuclear power production, with the country exporting its nuclear designs and technologies to East Asia and Europe.
The Fukushima Nuclear Power Plant was constructed in 1979 and was wholly owned by the Tokyo Electrical Power Company (TEPCO). The nuclear power plant had six units; unit 1 was commissioned in 1971. The total power capacity was 4.9 MW; the reactor was designed and supplied by General Electric, Toshiba, and Hitachi. It is worth mentioning that the Fukushima Nuclear Power Plant was the first plant that TEPCO managed to develop, construct, and operate completely. The plant consisted of six units of boiling water reactors. The plant was located in Lkuma (Futaba Fukushima Prefecture), which was two hundred and fifty kilometers north from Tokyo. The Fukushima plant encompassed a 3.5-square-kilometer area along the shoreline; it also had a sister plant Fukushima Daini Nuclear Power Plant, which was situated in Naraha and Tomioka (Fukushima Prefecture).
Regarding the reactors six units, General Electric supplied units 1, 2, and 6, Toshiba supplied units 3 and 5, while Hitachi supplied unit 4. Units 1, 2, 4, 5, and 6 operated on low enriched uranium fuel, whereas unit 3 operated on plutonium mixed oxide fuel. Moreover, units 1 to 5 were Mark I type light bulb torus of containment structures, unit 6 was a Mark II over/under containment structure , where Mark I and Mark II were TRIGA (Training, Research, Isotopes, General Atomics) pool-type reactors used for research and testing without containment building (General Atomics 2018).
Nature of the Accident
On March 11, 2011, an earthquake hit the Pacific coast of TMhoku with a magnitude of 9.0; it was the most powerful in Japan and fourth by magnitude in the world, according to United States Geological Survey (USGS 2011). As a result of the earthquake, a tsunami with a height of up to 40 meters was generated. Due to the TMhoku earthquake, the Fukushima Nuclear Power Plant, which consisted of six reactor units (BWR), experienced a shutdown. The electricity-generating reactors 1, 2, and 3 were shut down due to the safety control procedures by withholding their fission reaction by loading the control rods. Control rods are made of a material that can absorb neutrons and control the resection rate. As the reactors were unable to run and started cooling down through pumps, diesel generators were used to continue generating power.
However, the tsunami reached a height of thirteen meters and damaged the diesel generators. Even though the power plant had seawalls to protect against 10-meter waves, the tsunami waves were higher. Thus, the water quickly flooded the diesel generators, leading to an operational failure. Consequently, cooling pumps failed to in cool water and thus could not prevent rods from melting inside the reactor. Even the secondary emergency cooling pumps stopped, causing the melting of the rods, and then the reactor overheated. The worst scenario occurred when power plant workers could not operate the cooling system and were unable to restore power within control systems, and several hydrogen-air explosions occurred, leading to radioactive releases. The reason behind the explosions was estimated to be overheating due to the chemical reaction of zirconium with water, which produced hydrogen gas in immense quantities.
The Australian Radiation Protection and Nuclear Safety fact sheet mentioned that the tsunami, which resulted from the TMhoku earthquake, disabled the reactor heat exchanger and diesel generators (ARPANSA 2015). Also, the tsunami broke the reactors connection to the power grid. Flooding, debris, earthquake damages, and previous internal reactor events led to the reactor overheating due to several hydrogen explosions and fully melted cores of units 1, 2, 3.
According to the Lesson Learned from Nuclear Accident at Fukushima Daiichi report prepared by the INPO (2012), Fukushima consisted of six boiling water reactors (BWR). Unit 1 was a model III of BWR, unit 2 to 5 were model IV, and unit six was model V. During the TMhoku earthquake, which was followed by a tsunami, units 1 to 3 were in full operation while units 4 to 6 were on maintenance and refueling. Based on the report, explosions occurred in units 1, 3, and 4 were the result of hydrogen accumulation from the damaged fuel in reactor buildings. Accordingly, the release of radioactive substances to the ground level of the plant led to the significant loss of the structures primary and secondary containment integrity. Similarly to the 1986 Chernobyl accident that was rated level 7, the Fukushima accident also received a rating of 7 by the International Nuclear and Radiological Event Scale (INES).
It is essential to mention that immediately after the disaster, no health consequences (e.g., acute health effects or deaths) associated with radiation were reported in the general public (Leppold, Tanimoto & Tsubokura 2016). However, the results of 2015 studies conducted with samples of children from Fukushima showed no adverse health effects in one sample while pointing at high risks of thyroid cancer in another sample (Leppold, Tanimoto & Tsubokura 2016). Such findings led to the increased controversy over the effects of the radiation as well as the diverted attention from the real risks of post-disaster health issues.
Range and Character of the Disaster
Following the Fukushima accident, Japans environment suffered from large quantities of released radioactive substances. The radioactive materials were released both into the air and the ocean. According to IAEA (2014) report on radiation protection after the Fukushima Daiichi accident, the harmful releases that were released should be referred to as the source term (p. 4). Also, the source of the material depends on the characteristics and quantity of the radioactive substance. According to the IAEA (2014) report, the main materials that were released were iodine and cesium, in particular, 131I, 134Cs, and 137Cs. IAEA (2014) estimated that the releases into the atmosphere were 100-500 petabecquerels (PBq) 9 for 131I and 6-20 PBq for 134Cs and 137Cs.
Compared to the Chernobyl accidents, the releases from Fukushima were 10 to 20% higher. The main releases of radioactive materials into the marine system were 131I, 134Cs and 137Cs with smaller amounts of tritium (3H) and other radionuclides also being released (IAEA 2014, p. 4). The estimations of the released materials in the sea were measured as 3-6 PBq of 137Cs, 10-20 PBq of 131I and up to 1 PBq of 90Sr (IAEA 2014, p. 6). It is essential to mention that the releases into the sea were accompanied by the uncertainty regarding the quantities that depended on the mechanisms of such releases (IAEA 2014). Regarding the movement mechanisms that contributed to the release of harmful substances into the atmosphere and the ocean, the IAEA (2014) differentiated the released radioactive material into aerial and marine.
Aerial radioactive releases were only seen in small and minuscule amounts of radioactivity depositions in the IAEA member-states. Also, it is critical to estimate both of the cesium sources 134Cs and Cs137 since they can contribute to the future radiation levels since they are stored in the environment. The IAEA (2014) report mentioned that there were no changes in 137Cs deposition levels, but 134Cs deposition levels decreased due to their decay.
Marine radioactive releases traveled from Japan coast to the Pacific Ocean, specifically to the Northwestern Pacific (North America). On the coast of Japan, 137Cs levels were 68 MBq/m3 at maximum, 137Cs levels were 25 Bq/m3 in the Pacific Ocean, and 137Cs levels were Bq/m3 in the Pacific Coast of North America. Also, 3H Tritium and Strontium 90Sr levels were not contributing significantly to the marine environment. As mentioned in the IAEA (2014) report, 137Cs levels would be at 1 Bq/m3 by 2021. Regarding the safety level in Tokyo from the radioactive releases, it was estimated that iodine (I) and cesium (Cs) levels were elevated in and around the prefecture. Also, the safety levels of the harmful substances concentration should be monitored due to the increased risks for infants, whose thyroid gland can be affected by rising iodine levels in tap water. However, iodine and cesium levels were back to normal after a couple of days after the Fukushima accident. Moreover, radiation levels in Tokyo were stable (IAEA 2015).
Australian Radiation Protection and Nuclear Safety Agency fact sheet mentioned that a tsunami resulted from the TMhoku earthquake, which disabled the reactors heat exchanger and its diesel generators (ARPANSA 2015). Also, the tsunami disrupted the reactors connection to the power grid. Due to the combination of flooding, debris, damages from earthquakes, and other internal reactor events, the Fukushima reactor failed and produced a destructive hydrogen explosion that melted reactors 1, 2, and 3 completely. The severe explosions and the fully melted cores caused a release of radioactive materials into the air and water around the country in large amounts, leading to the evacuation of citizens within the 20- to 30-kilometer radius. Furthermore, the radioactive material was released into the air and water at 6.3 E17 Becquerels (Bq) of iodine-131 equivalent into the air, and 4.7 E15 Bq into the sea between March 11 and April 5, 2011, based on the estimations of the Nuclear Safety Commission of Japan (INPO 2012). In addition to evacuation, citizens who stayed in the affected area were instructed to stay in their dwellings and avoid going outside.
Long-Term Effects on Health
High levels of radiation caused adverse health complications, from which the population had to suffer. Both civilians and the plants workers were exposed to the radiation through external sources, inhalation, and ingestion. According to the World Health Organization (2015) survey conducted in Fukushima Prefecture, a damaging dose of harmful substances for adults was 10 mSieverts or less and 20 mSieverts for one-year-old infants. The concentrations of harmful substances were higher in locations near the plant. As mentioned in TEPCO (2018) records, the average workers effective dose was 12 mSievert in the first nineteen months. According to the UNSCEAR (2013) report, it was hard to estimate the level of risk for infants developing thyroid cancer in the future; however, as to the extreme doses that workers received, the risk of developing thyroid cancer and other thyroid disorders was higher. Also, the risk of developing cancer among the workers who were exposed to a 100-mSv dose was significantly higher. Long-term radiobiological health effects for humans can include thyroid cancer, leukemia, breast cancer, and prenatal complications. Although, the adverse health effects for each person depended on the level exposure, the effective dose, and their age.
On the other hand, the effects of non-human (biota inhabitants) from the Fukushima accident were related to terrestrial, freshwater, and aquatic ecosystems. The terrestrial ecosystem was affected by different concentrations of radionuclides. For example, terrestrial mammals and birds were exposed to 1.2 and 2.2 ¼Gy/h of harmful substances in areas with a 137 Cs deposition. Furthermore, rates of 300 ¼Gy/h were found in soil-dwelling organisms (UNSCEAR 2013). In the same report, there was also an observation of the declining numbers of birds and insects. The aquatic ecosystem was divided into freshwater and marine; the freshwater system did not reach the threshold levels for the chronic exposures, with the marine system showing low concentrations of harmful substances of 0.10-0.25¼Gy/h (UNSCEAR 2013). To address the complicated environmental situation, the government had to take action.
The exclusion zone was hard to manage during the Fukushima accident, with the Japanese government having to change its range several times since the fog prevented the public from seeing clearly. For example, the government asked those citizens who lived close to the Fukushima plant to move to other locations while the residents living within the 20-30 km radius from Fukushima Prefecture were asked to stay indoors and refrain from going out. Later, the government asked the citizens who stayed indoors also to evacuate. The increasing size of the exclusion zones and the changing evacuation areas were extremely hard to manage; the number of evacuated citizens reached 150,000 people. Evacuating procedures were limited due to the damage of Fukushima Prefecture, the lack of detailed arrangements, and poor medical supplies (thyroid blockers). Moreover, during the evacuation, disabled, elderly, and sick citizens were in much more difficult situations in the exclusion zones due to lack of proper arrangements.
Likelihood of the Accident Occurring in the Future
After the Fukushima accident, a lot of international organizations in the nuclear industry along with governmental officials improved designs, laws, and regulations to prevent any similar accidents from occurring again. However, no one can predict what would happen. According to Jungmin Kangs (2011) article for the Bulletin of the Atomic Scientists, several steps to prevent another Fukushima can be taken. For example, Kang (2011) suggested building a stable electrical supply system for nuclear power plants, so that any future incidents can be eliminated with the help of a stable supply of power. Also, it was suggested to install ventilation systems to release gases and limit any high gas pressures. Another suggestion was to store the wasted fuel in dry casks to avoid the melting scenario that occurred during Fukushima (Kang 2011). Moreover, a safe system for emergency power supplies (e.g., diesel generators) should be installed on higher levels of the plant and not in the basement like it was done at Fukushima, as mentioned by Rodney Ewing in his interview with Stanford News (Traer 2016). Besides that, Ewing talked about an improved risk assessment and evaluation model of geological hazards to predict any disasters in the future.
Nicole Jawerth from the IAEA Office of Public Information and Communication wrote an article Five years after Fukushima: making nuclear power safer to talk about the event and the lessons learned. Jawerth (2016) wrote that since the accident, many researchers analyzed the causes and consequences by carrying out stress test assessments and reevaluating the designs of existing nuclear power plants. For instance, the installation of backups for power sources, the addition of extended water supplies at reactors, protective tools such as reinforced walls, and improved organizational and regulatory systems were all proposed as long-term solutions to protect the environment from new disasters. However, the Tokyo Electric Power Company faced a lot of public criticism regarding the Fukushima accident because it was not transparent in issuing the details of the event and delayed evacuations. Also, they could have improved the design of the Fukushima plant based on the United States Regulatory Commission.
Conclusion
As mentioned in the paper, the Fukushima accident facilitated inspections of all nuclear power plants in Japan, and the government implemented more protective plans and regulations (including risk assessment of geological hazards) to prevent any future accidents and threats of climate change. As a result, the likelihood of similar accidents happening again can be minimized. For instance, a stress test was done all around the globe to evaluate the reactors after the Fukushima accident. Also, new nuclear power plants have been introduced (e.g., the third-generation AP1000) to contribute to the reduction of costs, enhance passive safety, and provide insurance in case of accidents. Therefore, despite its tragic outcomes, the Fukushima disaster led to innovations at nuclear power plants and contributed to the development of mitigation strategies that could be deployed to prevent any future nuclear accidents.
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