|Fig. 1: Map shoing the closeness of epicentre of the earthquake to the Fukushima nuclear power plant. (Source: Wikimedia Commons)|
After the two most significant accidents (Three Mile Island in 1979 and Chernobyl in 1986) in the 50 plus years of civil nuclear power generation, it was expected that along with the progress of safety and technology and the natural tendencies to learn from and not repeat consequential mistakes, any threat of nuclear disasters would be easily avoidable. 
This was the thought process before the 2011 incident at Fukushima. This 25-year incident-free wait period, has since revolutionised the modern outlook of the nuclear power industry. 
It certainly is difficult from a safety perspective to predict unforeseen circumstances such as natural disasters, which is how the incident at the Fukushima Daiichi nuclear energy facility came about. The issue can be divided into two parts;
On 11th March 2011, a magnitude-9 earthquakes occurred. This lead to the designed emergency shutdown of three operating reactors. The remaining three reactors at the facility were already shut down for refueling and maintenance. At this point all 6 reactors were safely shut down and kept cool by emergency safety power systems. This indicates that proper design parameters were taken into account relating to seismic ground activity. However, the main issue began when the off-site power supplies were cut off, which prompted the limited capacity on-site emergency diesel generators to start automatically. [1,3]
The earthquakes led to a massive estimated 45 feet tsunami wave, which struck the facility a short while later. Fig.1 shows the geographic location of the earthquake epicentre and the tsunami, along with the affected nuclear reactors. The consequence of the tsunami, in particular, was severe flooding that disabled all but one of the on-site generators. The result was that (although two of the already shut-down reactors were under safety operation) the safety systems in the first three reactors eventually failed after several hours of generator operation, resulting in overheating and melting their cores to some degree. [1,3]
Although the facility was decently prepared for the earthquake and seismic activity, the 45-foot tsunami that followed was much larger than the tsunami analysis accounted in the plant's design. It was then realized that years of poor regulation and inattentiveness to tsunami risks and inadequate safety controls had left the facility highly unprepared when natural disaster struck.  It is believed that enhanced defenses would have widened safety margins and might have mitigated the consequences of the tsunami. Poor understanding of Japanese regulators and the approach to key and essential hazard prediction for Fukushima Daiichi was valued to be in variance with international and in some cases Japanese best practices. 
The crisis immediately forced the evacuation of 150,000 people, many of whom have still to return home.  There is possible radiation poisoning of the atmosphere around the reactor, which is a possibility taken into consideration due to massive amounts of heat radiating from the reactor core vaporizing water vapor in the air during winters. There are also possibilities of radioactive particles leaking from the plant site poisoning the nearby Pacific Ocean fish and other seafood, endangering human life. [5,6]
The above listed are only apparent potential risks, however the more potent dangers are listed as follows. There is a real risk of health faced by people in the vicinity due to the delicate and dangerous work of cleaning the nuclear disaster site. The presence of radioactive rubble and undamaged fuel rods that need to be removed and an unknown amount of nuclear fuel required to be contained, makes the risks even higher. 
The plant was considering a short-term solution of heavy investment into multiple power sources and cooling systems, which would heavily add on costs and force temporary closure. However, this seemed like a necessary option at the time. [1,7]
Safety is the nuclear energy industry's highest priority, and it is standard practice for the industry and federal regulators to review events that occur internationally to glean information that can help make facilities even safer. From the Fukushima Daiichi nuclear plant incident, the most important lesson learnt is that a nuclear energy facility should be well prepared to handle catastrophic natural disasters simultaneously at multiple reactors, regardless of the cause.  Multiple nuclear facilities around the world and regulatory bodies initially issued new requirements and requested detailed information from the incident in Japan in several areas to understand what really occurred and how it could be prevented. Within few days of the incident, reviews of safety equipment and procedures were conducted at many nuclear energy facilities to verify that implemented safety measures were in place to cope with severe unexpected events. [2,7]
Mitigation strategies were implemented to maintain reactor and used fuel pool cooling (with instrumentation to monitor parameters) and containment integrity in case of a possible severe event that exceeds design parameters.Another strategy was to install readily accessible hardened vents for heat removal and pressure control in boiling water reactors with containments like the reactors at Fukushima. 
Following the incident, the risks of floods threatening the safety of nuclear reactors are taken far more seriously and following implementations were taken into consideration, some still take effect today.
Plants have been re-evaluating the flooding hazard at their sites using state-of-the-art methods. An assessment was performed about the effects of the new flood information obtained from the sites at Fukushima (from 2015), to ensure that mitigating strategies were in place to cope with the flood hazard, at some sites assessments are still going on today.
Sites that face a more significant flooding challenge will complete integrated assessments of potential flooding effects on key plant components. These assessments are expected to be completed by the end of 2018. Based on the results of the integrated assessment, the particular company may need to take additional steps to enhance flood protection [1,8]
Regulations regarding seismic activity in certain areas has also tightened with time, since 2015. Seismic experts have been re-evaluating earthquake protection at nuclear power plants using the latest available data and methodologies and based on the results of the studies, some companies will perform more detailed evaluations of their plant's ability to withstand stronger ground motion than they originally expected. The evaluations and final checks are expected to be completed by 2019 in some areas. [2,8]
The proposed rulemaking on mitigating strategies also includes new requirements to maintain staffing and communications equipment necessary to successfully respond to an extreme event. The proposed rule will require companies to conduct period drillsin addition to those regularly carried out at plant sitesto demonstrate the capability to implement a variety of enhanced emergency response strategies. 
Compliance between all nuclear power stations around the world also seems an issue for all strategies and rules implemented, which seems to be affecting prompt action, since the incident in 2011. If the stricter regulations are not abided by, this can lead to an increase in costs faced by the companies (nuclear power) to reinforce safety strategies. [1,8]
The resulting three of Fukushimas reactors were into melt-down, was shocking to the world. Japan, a fully industrialized country with high safety requirements, was facing a nuclear disaster uncommon for so many years. As a result, many countries reviewed their energy policies. 
Before the accident, 442 nuclear power reactors in 30 countries produced 14% of all world's electricity. This number dropped to just 11% in 2012, as 15 reactors exited service; mainly in Germany and Japan. 
After the Fukushima disaster, Japan pulled back its nuclear ambitions, ordered large-scale inspections and introduced new safety regulations. All of its 48 remaining reactors have been kept offline.
Germany shut down eight of its oldest reactors almost immediately after Fukushima, focusing instead on renewable energy, and phase-out all of its nuclear power by 2022.
Switzerland adopted a similar approach when the government decided not to build any new reactors and phase out its nuclear production by 2034.
But not all countries have drawn back ...
Both France, which has the world's highest share of nuclear power for its electricity production, and the U.S., the world's largest producer, reaffirmed their positions on the power source. Both countries continue to invest heavily into safety improvements. Most of the safety improvements listed above are incorporated by these countries. 
All four "BRIC" countries are boosting their nuclear power production, with India aiming to supply 25% and Russia 45% of their electricity from nuclear power by 2050, and Brazil planning to build five new reactors by 2030.
China is facing pressure to cut its pollution levels and reliance on coal. It already operates 20 reactors and aims to more than triple its nuclear capacity by 2020. [2,9]
© Valmik Lakhlani. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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