Since the IAEA mission it has emerged that, in , TEPCO did in fact perform some preliminary computer modeling that tentatively suggested the tsunami hazard to the plant had been severely underestimated. These simulations assumed a repeat of the AD earthquake. Given the new simulations were based on an actual historical earthquake, they should have been followed up on immediately. Had the results been verified, TEPCO may have been able to take corrective action in time to avert the disaster of March 11, Following the publication of new earthquake safety guidelines and the earthquake that affected the Kashiwazaki-Kariwa station, the seismic design basis for all Japanese nuclear power plants was reevaluated and at some, including Fukushima Daiichi, it was increased.
Under a process known as back checking, no work was required at plants—including Fukushima—that already met the revised guidelines.
Indeed, there was clearly some concern about this problem among Japanese utilities. For instance, when Chubu Electric Power Company chose to expand the seismic design basis for its Hamaoka Nuclear Power Plant actually prior to , it did undertake physical improvements at the plant, even though they were not required under the back-checking process, in order to widen safety margins and hence mitigate the consequences of a beyond-design-basis earthquake.
Third, a fundamental principle of nuclear safety is the existence of an effective and independent regulator to set safety rules and to ensure compliance with them. By contrast, computer modeling of tsunami safety was called for as early as the first IAEA guide on flooding hazards at coastal nuclear power plants published in In short, NISA appears to have failed in its responsibilities to review compliance with tsunami safety standards and also to update them in light of both emerging new evidence and evolving international standards.
Had international standards and best practices been followed, the scale of the natural disaster on March 11, , might have been predicted, giving TEPCO the opportunity to enhance plant defenses. In any case, the accident sequence dramatically demonstrated that the plant was not equipped to cope with the events of March Could the plant have been better prepared?
Just a few weeks before the accident, NISA gave unit 1 the green light to operate for an additional ten years. Japan is a densely populated, highly industrialized country with few energy natural resources. The assessment is mainly focused on equipment and structures having a safety function and specifically addresses aging issues.
The focus is on selected equipment that may suffer age-related degradation and failure, not on safety weaknesses related to the design or configuration of the installation. Japan is not unique in concentrating attention on the status of aging equipment during reactor lifetime extension examinations.
This is also the case in other advanced nuclear programs. In February , just one month prior to the Fukushima accident, NISA granted TEPCO a ten-year operating license extension for unit 1 after a technical review and some modifications that were carried out the year before. Though Japan was quite slow to adopt firm regulations for protection against the tsunami threat, it was not for lack of knowledge of proper guidelines and review processes.
Japan, like many other advanced countries, requires periodic safety reviews to assess and update the safety status of nuclear installations at ten-year intervals. On the basis of this activity, TEPCO and Japanese regulators should have taken well-understood and straightforward engineering measures to better protect the Fukushima Daiichi Nuclear Power Station before the accident occurred.
According to these experts, on the basis of international knowledge accumulated during the four-decade operating lifetime of the Fukushima Daiichi Nuclear Power Station and put into practice at nuclear power plants elsewhere, TEPCO, encouraged by Japanese regulators, could have taken some or all of the following actions to have protected the plants against a tsunami:.
When the Fukushima Daiichi station was constructed, the emergency diesel generators and emergency batteries were installed on the floor inside the plant building to afford protection against earthquakes. Ventilation ducts in the compartments where this equipment was located were not waterproofed. Moving this emergency power equipment to higher ground, safety experts said, would not have increased its vulnerability to seismic shock, provided it was fixed to a platform designed to resist earthquakes.
Prior to the tsunami, JAPC had partially implemented plans to erect a wall to prevent tsunami water from flooding two pits at the plant where seawater pumps were located and to make the pump rooms watertight. The wall was erected before the tsunami occurred. Water entered one of the pits because spaces where pipes penetrated into the pit had not yet been made watertight before the accident. In that pit, a seawater pump that provided cooling for an emergency diesel generator was damaged and unable to function, forcing JAPC to shut down the generator.
But no flooding occurred at the other pit where pipe penetrations had been made watertight. Had JAPC not carried out these upgrades, it would almost certainly have lost all three emergency diesel generators, potentially resulting in a much more serious accident.
Within just a few weeks after the accident at Fukushima, Japanese nuclear power plant owners began announcing concrete plans to make widespread and significant plant design changes and other upgrades. On site, spare equipment for the seawater pumps will be stored in a bunkered facility and heavy earth-moving equipment will maintained. Some senior Japanese government and industry experts interviewed for this paper privately concurred that, had TEPCO and regulators taken these steps before, a severe accident with significant off-site radiation releases could have been avoided.
But before the accident the will to make these changes was not there. During the four decades that the Fukushima Daiichi Nuclear Power Station was in operation, nuclear safety authorities and nuclear power plant owners in several countries were establishing requirements and configuring nuclear power plants in ways that could potentially have saved the Fukushima Daiichi nuclear station from disaster had they been heeded. In particular, some regulatory bodies outside of Japan reassessed the safety of installations in the event of extreme flood hazards, a station blackout, and the loss of the ultimate heat sink.
In the view of safety experts participating in such assessments, had Japan acted on these developments, the plant could have survived the tsunami that struck in March Compared to some nuclear power plants in other countries, the units at Fukushima Daiichi were considerably less protected against a loss of internal and external AC power on the site. In addition to the lack of waterproofing and bunkering that proved fatal to the emergency power supplies at Fukushima Daiichi, most of this equipment was water cooled, not air cooled as is the case for more modern nuclear power plants.
The water-cooled diesel generators required a cooling water system connected to the ultimate heat sink. There are ample instances of international review processes that have led to upgrades that can help protect nuclear power plants against station blackouts. For example, in the United States beginning in , the Nuclear Regulatory Commission required that a nuclear power plant withstand a complete loss of AC power for between four and eight hours, depending on specific conditions.
Some senior European nuclear safety experts expressed the view that the Fukushima Daiichi units in fact likely met the U. Unit 1 featured an isolation condenser and units 2 and 3 were equipped with reactor core isolation cooling systems using turbine-driven pumps. In Germany, the requirements to protect a nuclear power plant against a station blackout are specified in the regulatory document KTA All German plants have at least one additional standby grid connection and more emergency diesel generators, with at least two of them being protected against external impacts.
The situation in some nuclear power plants in some other European countries is similar. Each unit at the three-unit Olkiluoto Nuclear Power Station in Finland, to give another example, is equipped with four emergency diesel generators necessary for a safe shutdown in all postulated conditions. Each emergency diesel generator is in a fireproofed compartment located well above the design-basis flood level calculated for the plant.
There is also an air-cooled gas-turbine power plant backing up the emergency diesel generators. That power plant is located above the design-basis flood level for the station, is in a separate building, and features two separate generator units, each having two gas turbines. Each of the four gas turbines can supply more than enough power for all three nuclear power plants at Olkiluoto. In the aftermath of the accident at Fukushima, Japanese experts have drafted new, revised, and more stringent requirements for coping with a station blackout at a nuclear power plant.
The March 11 tsunami disabled seawater pumps and all associated electrical and mechanical equipment at Fukushima Daiichi.
Without an alternate heat sink, the plant was left without a way to cool its reactors. As it turns out, this absence of an alternate heat sink is a problem in other countries as well. Unlike the case for hardware defenses against a station blackout, post-Fukushima examinations by European Union country regulators testify to an absence of national requirements for providing backup alternate heat sinks to cope with a severe external event.
But several owners of nuclear power plants in these countries, in consultation with regulators well before the accident in Japan, had provided alternate heat sinks that would be available in the case of a severe external event. These include the Borssele nuclear power plant in the Netherlands, which in the case of the loss of the main riverine heat sink is served by a system designed to be redundant and hardened against the impact from external events that vents steam via relief valves. It is also served by eight deep water wells designed to be seismic and flood resistant.
River water pumping and intake equipment for the Swiss and Dutch plants is also designed to maximize reliability in case of postulated severe external events. This reserve system is situated in a separate building from the seawater pumps, enhancing redundancy although the EU-mandated stress test on this reactor did identify some potential flooding vulnerabilities that need to be rectified. Particularly noteworthy are measures taken by Taiwan to protect its nuclear power plants against a severe tsunami by taking advantage of the physical geography of the plant layout.
Like Japan, a number of reactors on Taiwan are located on the Pacific coast and the plant sites are vulnerable to extreme seismic events. To avoid the loss of the ultimate heat sink in the first place, the two-unit Chinshan boiling water reactor nuclear power station, built during the s to essentially the same design as Fukushima Daiichi units 2 and 3, was designed to withstand a tsunami having a maximum amplitude of The plant was therefore built at 12 meters.
In addition to emergency diesel generators located inside the plant and above the level of the postulated design-basis tsunami, two gas turbine electricity generators are available at an elevation of 22 meters.
In the case of the loss of the primary heat sink, for emergency cooling, two water reservoirs were installed at an elevation of 62 meters. At Kuosheng, another site on Taiwan hosting two older boiling water reactors, the nuclear power plant was constructed at an elevation of 12 meters above sea level, above the design-basis tsunami of Two emergency gas turbine generators were installed at 22 meters, and two water reservoirs are located at 90 meters.
In December , a storm surge at high tide exceeded the design-basis flood scenario for the Blayais Nuclear Power Station in France, causing flooding at two units and a partial loss of power. The storm also resulted in the loss of some telecommunications links and road access to the site. Examination by French authorities revealed that dikes were too low and that rooms containing emergency equipment were insufficiently protected from flooding.
Recognizing that the Blayais event represented a systemic failure in hazard assessment, all nineteen nuclear power stations in France were thereafter ordered by regulators to identify all phenomena that could cause a flood, and to reassess site-specific flood management protection with regard to loss of off-site power, communications, and heat sinks.
Some plants were required to raise dikes and walls. All had to waterproof building substructures, plant areas where floodwater could intrude, and rooms containing emergency equipment.
Between and the Blayais event was also studied at the Nuclear Energy Agency of the Organization for Economic Cooperation and Development, of which Japan is a member. It made some recommendations to upgrade the plants, not all of which had been implemented by the time of the Fukushima accident.
Protection against flooding and other external events are assessed during the periodic safety review process for many nuclear power plants worldwide. But after an initial periodic safety review for these plants was carried out during the s, a separate building was built to house additional cooling sources and emergency diesel generators and to protect these in the case of an external event. These reviews considered specific scenarios where more than one external cause resulted in a severe event; thereafter, the height of the design-basis flood was increased from 9.
Finally, a growing divergence between their practices and evolving international standards should have alerted NISA and TEPCO to potential problems in their approach to tsunami risk assessments. In , the IAEA published a safety guide on flood hazards for nuclear power plants, which contains guidance concerning all factors that must be considered in assessing the risk from tsunamis.
The IAEA more forcefully injected itself into the issue of tsunami safety following a December tsunami that ravaged many seacoast areas in the Indian Ocean and shut down a nuclear power plant in India. A revision of the safety guide was developed with the participation of the World Meteorological Organization incorporating updated criteria and recommendations and integrating meteorological and hydrological hazards.
A specific project, mainly supported by Japan and the United States, was launched in relation to tsunami hazard assessment methodologies. Japan participated actively in the implementation of the project, but the IAEA findings were not translated into practice in time to protect Fukushima Daiichi from the tsunami in There is no simple answer to the question of why there were major safety deficiencies in the protection against tsunamis at Fukushima Daiichi and other Japanese nuclear power plants.
This paper does not intend to provide conclusive answers to these questions. Following the Fukushima accident, there has been much more extensive domestic and international criticism of the Japanese regulatory system. However, until now, a comparative lack of independent expertise in Japan may have rendered NISA overreliant on them.
Most obviously, industry experts on loan to the regulator may be reluctant to criticize their employers. Solving this problem will require a large and long-term investment in human resources. The U. When the era of commercial nuclear power generation began nearly a half century ago, safety experts initially were most concerned about the possibility that a serious accident would be caused by a sequence of events unfolding inside the plant—such as that leading to the Three Mile Island accident in the United States in and to the explosion at Chernobyl in Only gradually did concern become focused on the possibility that an extreme external event could cause a reactor to fail.
And in some nuclear programs over time specific threat assessments for external events have changed. By contrast, Japan has been much slower to appreciate the potential danger of some other external events, especially tsunamis. A government-appointed investigation committee, headed by Yotaro Hatamura, Professor Emeritus at the University of Tokyo, explained in an interim report from December , that.
The risk of [a] tsunami exceeding design basis [was] not considered. Staff education was not organized for such [an] eventuality and equipment and materials for such recovering operations were not ready for use. TEPCO did not take precautionary measures in anticipation that a severe accident could be caused by a tsunami such as the one [in March ]. Neither did the regulatory authorities. Why this should be the case might be explained at least in part by deficits in regulatory quality and independence as discussed above.
Some Japanese government officials interviewed for this paper asserted that NISA had no authority to impose tsunami-related standards and plant design modifications on nuclear power plant owners. Some industry executives claimed instead that NISA did have this authority. In court, the government argued it was impossible to predict the tsunami or prevent the subsequent disaster.
Tepco said it had fulfilled its compensation responsibility under government guidelines. Plaintiffs said the ruling brought some justice, but that their lives could never return to normal and their struggle was far from over.
This article is more than 1 year old. Plaintiffs and their supporters march in Japan ahead of the court ruling in Sendai on the tsunami-crippled Fukushima Daiichi nuclear power plant disaster on Wednesday.
Fukushima unveils plans to become renewable energy hub. Lacking tsunami specific training, certification and licensing, the potential for similar mistakes to occur in hazard studies for other coastal nuclear power plants exists, he said. He points to recent studies around the world where lack of experience and context produced tsunami inundation projections with Fukushima-size underestimation of the hazard. A new report authored by USC researchers has estimated that millions of people may still be suffering from mental and physical health problems related to the Chernobyl accident.
Najmedin Meshkati has been selected as a member of a new committee to study the lessons learned from the Fukushima nuclear accident. What do get when you put eight writers and 10 directors at the helm of a single feature film? Murad Jah has been a research assistant for the COP26 conference for a year.
Wake-up call During the disaster, tsunami heights reached an estimated 13 meters at Fukushimi Daiichi — high enough to flood all of the backup generators and wash away power lines.
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