Our positions on the issue of earthquakes and nuclear power plants in the Japanese archipelago differ significantly, depending on how we see the present “Fukushima genpatsu shinsai.” Here, the “Fukushima genpatsu shinsai” refers to a catastrophe unprecedented in human history, a combination of almost the Japan’s worst earthquake and tsunami disaster caused by the great off-Tohoku earthquake of March 11, 2011 with a magnitude (M) of 9.0 on the Richter scale, and a large-scale radioactive leak accident at the Fukushima Dai-ichi nuclear power plant operated by the Tokyo Electric Power Co., Inc. (TEPCO). It is not the worst picture that the author had in mind when he proposed the term and concept of gempatsu shinsai (referring to an earthquake-nuclear combined disaster) [1. For English reference of gempatsu shinsai, see Ishibashi (2003) presented at http://historical.seismology.jp/ishibashi/opinion/2011touhoku.html] in an article in Kagaku (October 1997 edition). However, there is no prospect of the disaster ending soon, and the radioactive contamination of the atmosphere, the ground, inland waters, the sea and all creatures continues to expand.
The author sees the Fukushima genpatsu shinsai as an historical event in which the Japanese nation faced an inevitable consequence after recklessly constructing more than 50 large-scale nuclear reactors for power generation on the coast of a quake-prone archipelago in defiance of nature. The author sees this as comparable with Japan’s military defeat in 1945 and, although the metaphor may not be quite apt, cannot help but see an analogy between the past, present and future of nuclear development in Japan and what happened in the country before, during and after the Asia-Pacific War. The peculiar nature of Japanese society caused the nation to wage war and eventually lose it as is written in Hando Kazutoshi’s Showashi 1926-1945 (History of the Showa Era, 1926-1945; published by Heibonsha in 2009). Similarly, thoughtless ambition in nuclear development amid earthquake risks and the resulting catastrophe could well be unique to Japan.
This paper does not discuss the burning issue of short-term and long-term actions to be taken in dealing with the Fukushima genpatsu shinsai. Although it will continue to trouble the Japanese people and the rest of the world for a long time even if the plant manages to extricate itself from the direst scenarios, what to do with the Japanese nuclear power plants as a whole after this setback is another urgent question, which is the point of this paper.
The following outlines why the author regards the event as a fiasco born from reckless behavior.
Japan accounts for nearly 10% of all global seismic activity. On this small island country, as many as 57 large-scale reactors, or more than 10% of the world’s nuclear reactors for power generation, have been constructed since about 1960. (This figure includes three decommissioned reactors and other reactors that are currently not in operation, including six reactors at the Fukushima Dai-ichi nuclear power plant.)
Japan’s nuclear power plant construction gathered pace in the late 1960s. In those days, however, the two basic theories of modern seismology (which includes the study of tsunamis), namely the theory of seismic faulting and plate tectonics, had yet to emerge. There were very few studies on active faults either. In addition, the Japanese archipelago was in a seismically quiescent period, which lasted until around the 1995 Kobe earthquake of M 7.3. Although there were several tremors that caused damage, nuclear power plants continued to proliferate without any being subject to powerful seismic shocks.
Under these two unfortunate circumstances, a majority of power plants, including the Hamaoka nuclear power plant of the Chubu Electric Power Co., Inc. in Shizuoka Prefecture, were built just above huge plate boundary fault planes or in other dangerous areas such as those with a high density of active faults, underestimating the power of earthquakes and tsunamis tremendously. Likewise, when construction of Unit 1 of the Fukushima Dai-ichi nuclear power plant was authorized in 1966, it was utterly unknown that it is situated in the frontal part of a tectonic plate to which northeast Japan belongs, subduction of the Pacific plate beneath northeast Japan is ongoing, and there exists a huge plate boundary fault plane in front of the site. [2. Results of the examination performed by the Committee on Examination of Reactor Safety of the Atomic Energy Commission (Note: At the time, the Nuclear Safety Commission was still non-existent.) in response to an application for authorization of construction included some optimistic remarks. One such remark reads: “The area around Fukushima Prefecture, excluding the district around Aizu, is one of the regions with low seismicity in Japan. In particular, the area near the reactor construction site has never been hit by any earthquake.” Another says: “The sea level at the actual site is not monitored, but according to the observation records at Onahama Port (located nearly 50 kilometers to the south of the site), the sea level was 3.1 meters at the highest and minus 1.9 meters at the lowest during the tsunami triggered by the 1960 Chilean earthquake.” This is how approval was granted to construction of a nuclear power plant at a site of about 10 meters above sea level developed by cutting a hill facing the Pacific. Given that nothing is changed once it has begun in Japanese society, it is then that the fate of the Fukushima Dai-ichi nuclear power plant and Japan were basically decided.] Essentially, the whole Japanese archipelago is the most dangerous place on Earth to locate nuclear power plants, since this is the subduction zone of the Pacific plate and the Philippine Sea plate and, at the same time, the mobile belt at the eastern margin of the Amurian plate. Yet seismologists had nothing to say about it. The pro-nuclear group, the media, opinion leaders and the general public remained unaware of the danger until recently.
When the Nuclear Safety Commission (NSC) of Japan revised the “Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor Facilities” (hereinafter, the “Revised Guide”) in 2006, the Nuclear and Industrial Safety Agency (NISA), Japan’s regulating body for nuclear power plants, asked power companies to perform the seismic safety back check, to evaluate and check the seismic safety of their existing power plants in accordance with the Revised Guide. At the moment, the reports produced are being discussed and this process has already been completed in some cases. Basically, back-check reports that cannot be regarded to be safe have been accepted although in some cases slight reinforcement has been made.
When discussing nuclear power plants in Japan, it is imperative to consider four points. First, the safety of nuclear power plants must be much greater than that of any other facility, given that they hold a huge amount of radioactive material. Even those who have hitherto been indifferent must now be aware of that. Second, nuclear power technology is not yet perfect. Third, the largest-scale aspects of earthquakes are really violent. And fourth, the human understanding of earthquake phenomena is still far from sufficient and there are plenty of issues that cannot be predicted. In thinking objectively about these four points, any rational, sensible person would understand how dangerous it is to place more than 50 large nuclear reactors along the coast of quake-prone islands.
Safety comes in two forms. One is the safety secured by control and the other is intrinsic safety. If you say that there is no problem in building nuclear power plants on quake-prone islands, you are referring to the first type of safety. Intrinsic safety is attained by not building the plant. Controlled safety is an attempt to command nature with limited human knowledge. It collapses the instant nature goes beyond human ability. Dr. Irikura Kojiro, a strong-motion seismologist who serves the NSC as chair of the Special Committee on Seismic Safety Evaluation, remarked in a Jiji Press story distributed on March 27 that Japan’s nuclear power plants really would not have been dangerous if an exhaustive analysis was made. That is an incredible comment. “They must be designed to remain safe if any unforeseen event takes place. (…) This should be the philosophy of designing nuclear power plants.” “Awareness of the power of nature is vital in designing them.” He also made these comments in an interview carried in the morning edition of the Tokyo Shimbun on April 5. The author thinks that according to human wisdom, awareness of the awesome power of nature should dissuade us from building any nuclear power plant and wonders why Irikura is so enthusiastic about such a terrible attempt. Moreover, his thought would probably be labeled as the meaningless theory of a scientist by those engaged in practical engineering work.
In short, it was reckless to construct multiple nuclear power plants along the coastline of an earthquake-prone archipelago. Around 1995, nature began to warn the Japanese incrementally as the archipelago entered a seismically active period. First, the Kobe earthquake shattered the myth about safety based on Japan’s earthquake engineering. However, the NSC published a report in September 1995, stating that the seismic safety of Japan’s nuclear power plants was not impaired by the Kobe quake. In October 2000, the Tottori-ken Seibu earthquake of M 7.3 took place in the area where no active fault had been known. That was a heavy blow to the myth about active faults in the seismic design of nuclear power plants. This was followed by the 2005 August off-Miyagi-Prefecture earthquake of M 7.2, and then by the Noto Peninsula earthquake of M 6.9 in March 2007.The former hit the Onagawa nuclear power plant run by the Tohoku Electric Power Co., Inc. and the latter, the Shika nuclear power plant operated by the Hokuriku Electric Power Co., Inc., and both plants experienced earthquake ground motion that exceeded the seismic design standard at each plant.
In July 2007, the Niigata-ken Chuestu-oki earthquake of M 6.8 brought about seismic ground motion far beyond expected levels to TEPCO’s Kashiwazaki-Kariwa nuclear power plant, and caused massive damage to all seven reactors. Since three reactors that were in operation and another reactor that was in the start-up phase automatically came into a halt, and the radioactive leak was slight, some asserted that the seismic safety of nuclear power plants had been empirically confirmed. However, that was a mere result of good luck. In fact, the magnitude (M) of the earthquake was not large and there was no successive occurrence of large aftershocks. In addition, not all seven reactors were in operation. NISA and the NSC carried out merely nominal checks on the soundness of equipment and the seismic safety of damaged reactors in many inquiry meetings, while ignoring a long submarine active fault that was thought to exist. They have to date approved the resumption of operations at four reactors by making “fake” confirmation of their seismic safety.
The author stated that the earthquake damage to the Kashiwazaki-Kariwa nuclear power plant was the final warning from nature and that neglecting this warming could result in the gempatsu shinsai, the third massive exposure to radiation after Hiroshima and Nagasaki. The author called for a drastic remedying of deficient safety regulations, to perform an overall review of the disaster risks of existing nuclear power plants and to consider closing and reducing them step by step in order of risk level. Unfortunately, however, few Japanese people shared this sense of crisis, and so the Fukushima gempatsu shinsai occurred, almost as if preordained.
In the light of the mentioned above, it is clear what needs to be done. We need to humbly learn the lessons from the error that led to this fiasco and to remove nuclear power plants from our quake-prone islands. To do this, it is imperative to completely rewrite policies in all fields, including energy, industry, economy, and regional affairs. It is quite similar to the rebuilding of the new Japan after the war defeat in 1945.
Naturally, it is unrealistic to immediately close all nuclear power plants, but we must swiftly identify high-risk plants across the country and shut them down. It has been speculated that the seismically active period would last until around the great Tokai-Tonankai-Nankai earthquakes that are expected to occur until the middle of this century. After March 11, however, it is possible that large earthquakes may now be much more likely in all parts of the Japanese archipelago, albeit not everywhere. This makes action truly urgent.
The riskiest plant is the Hamaoka nuclear power plant just above the fault plane of the hypothetical Tokai earthquake. It is followed by a cluster of nuclear power plants in the Wakasa Bay region where large earthquakes are possible and many active faults are distributed. These include Unit 1 of Tsuruga nuclear power plant run by the Japan Atomic Power Co., Units 1 and 2 of Mihama and Unit 1 of Takahama nuclear power plants both operated by the Kansai Electric Power Co., Inc. All of these reactors have already been in service for more than 36 years. Another at-risk plant is the Kashiwazaki-Kariwa nuclear power plant where the soundness of facilities hit by the 2007 quake is uncertain and the risk of its aftershocks occurring just beneath the plant is yet undeniable.
It is necessary to classify individual plants, from the viewpoint of danger, in a reasonable and objective manner in consideration of the length of operation, such as more than 30 years, reactor type, accident record, ground conditions, topographical features, ground altitude, earthquake and tsunami-related environment (including active faults), climatic and marine conditions, and social circumstances. This process should be made transparent to the public, possibly by a new organization set up in the Cabinet Office. There is no reasonable argument for continuing the nuclear fuel cycle project and it must be discontinued immediately; therefore the nuclear fuel facilities in Rokkasho-mura and Tokai-mura and the Monju fast breeder reactor should be closed down. The facilities in Rokkasho-mura and the Monju reactor have been at very high risk, as they lie just above active faults. At the moment, construction of three reactors is underway, and preparations are being made to build another. This work should of course be halted. Specifically, we are talking here of the Oma nuclear power plant of Electric Power Development Co., Ltd. and the Higashidori nuclear power plant belonging to TEPCO, both of which are in Aomori Prefecture, and the Shimane nuclear power plant Unit 3 of Chugoku Electric Power Co., Inc. in Shimane Prefecture. The preparation work is being carried out by Chugoku Electric Power Co., Inc. at Kaminoseki in Yamaguchi Prefecture. Any new plant construction is out of the question.
NISA, on its view that the serious accident at the Fukushima Dai-ichi nuclear power plant was caused by tsunami, issued individual electric power companies with an instruction on March 30 to carry out emergency safety measures against tsunami. These sound like follow-up or improvisational measures, although they are better than nothing. “If any nuclear power plant in Japan suffers another earthquake, it may be a tsunami that causes the damage. As is shown at the time of the giant tsunami in the Indian Ocean, there are still many unknowns even to earthquake and tsunami researchers. So, the tsunami issue is very important.” These were comments made by the author as the Niigata Prefectural Government’s subcommittee on earthquake and geology related to the 2007 Kashiwazaki-Kariwa plant’s earthquake damage held its 23rd session on March 25, 2010 to discuss the safety of Units 1 and 5 of the plant against tsunami. But, at this moment after March 11, should another disaster occur, it may not be a tsunami but a multiplexed blow of strong ground motions caused by the main shock and aftershocks or by successive earthquakes, or any other phenomenon such as a co-seismic crustal movement.
All aspects of the nuclear energy policy and the nuclear safety administration should be radically restructured with a view towards ultimate denuclearization. As in the case of dismantlement of the Imperial Japanese armed forces in 1945, Japan faces another major challenge in dismantling the powerful industry-government-academia complex that has pushed ahead with nuclear development. This, however, does not mean that public administration and engineers for nuclear safety are no longer needed. Some nuclear power plants will continue to operate and it is very important to implement long-term safety control at closed nuclear power plants. Indeed, a large number of skilled and highly-motivated engineers are required for ensuring safe ending of nuclear power. While guides for construction of new nuclear power reactors are no longer necessary, there is an urgent need to draw up reasonable standards for risk classification and stringent guides for ensuring the safety of facilities before and after closures.
It is said that the accident at the Fukushima Dai-ichi nuclear power plant took place as a giant tsunami with a height of 14 to 15 meters, which exceeded the assumption of 5.7 meters, disabled all emergency power generators and hampered core cooling. Dr. Irikura, as well, showed his view in aforementioned articles in Jiji Press and the Tokyo Shimbun, claiming that the earthquake ground motion caused no problem. However, this could be a serious misunderstanding. Ascribing the accident to the tsunami alone is very dangerous to debates on the seismic safety of existing nuclear power plants in Japan and beyond.
Tanaka Mitsuhiko wrote articles in Sekai and Kagaku (both, May 2011 edition) on the seismic vulnerability of the Fukushima Dai-ichi nuclear power plant. Concerning Unit 1, he infers that a violent earthquake ground motion caused damage or fracturing of the piping and that a critical loss-of-coolant accident (LOCA) occurred irrespective of the tsunami or station blackout (SBO; total loss of AC power) on the basis of an analysis of temporal changes in water level and pressure in the reactor pressure vessel and in the pressure in the containment vessel, as well as analysis of the conditions under which the hydrogen explosion occurred in the afternoon of March 12. A LOCA is an accident as severe as a runaway. Concerning Unit 2 as well, he thinks that the hydrogen explosion near the pressure suppression chamber on March 15 resulted from damage to the chamber caused by the earthquake motion.
The earthquake records also imply the possibility that the ground motion caused serious damage to the plant.
Incidentally, with respect to Unit 5 of the Fukushima Dai-ichi plant, an interim report by TEPCO on the seismic safety back check was reviewed. It was consequently rated as appropriate by NISA, which was also approved by the NSC. Based on that, the maximum acceleration of the design basis earthquake ground motion (DBEGM), which is used for seismic design, formulated on a hypothetical ground on site (free surface of the base stratum) was 600 gals (a unit of acceleration) in the horizontal direction and 400 gals in the vertical direction. It was judged that the seismic safety of the facilities, i.e., the buildings, other constructions, devices and piping systems, would be ensured for this DBEGM.
Now, on April 1, provisional data as part of the seismic observation records of the March 11 main shock obtained at the Fukushima Dai-ichi and Fukushima Dai-ni nuclear power plants were finally made public. The focus of attention is whether the DBEGM was exceeded or not. However, the published data were those on the basemats (the lowest underground level) of the reactor buildings and could not be directly compared with the DBEGM. Therefore, the author makes comparison between the observed maximum acceleration and the maximum response acceleration calculated for DBEGM, both on the basemats. In the Fukushima Dai-ichi plant, the observations in the east-west direction were 550, 507 and 548 gals at Units 2, 3 and 5, respectively. They were higher by 15 to 26% than the response values, specifically 438, 441 and 452 gals, respectively. Observed values in the east-west direction at Units 1 and 6 were close to the response values. In the future, the earthquake ground motion on the free surface of the base stratum will be back calculated from the observed data and compared with the formulated values of 600 and 400 gals of DBEGM, and the response spectrum showing the property of the earthquake ground motion will be scrutinized.
Even at the current stage, however, it can be said that the DBEGM was an underestimate and that seismic safety was not secured. In other words, both TEPCO’s interim report and the assessments made by NISA and the NSC were inadequate. Despite that NISA and the NSC had confirmed that the key safety functions – namely, shut down, cool and confine – would be secured for Unit 5, the cooling function may have been lost for Unit 1 and the confining function for Unit 2 (here, TEPCO had reported that these three functions would be also maintained for units other than Unit 5). This fact has significant implications, namely that it is imperative to radically modify the Revised Guide, to completely change the examination system, and to redo the seismic safety back check on nuclear power plants all over the country.
On April 2, a crack was discovered on the seaward side of the wall surface of the concrete pit near the water intake for Unit 2. From this crack, a leakage of high concentration radioactive water to the sea continued until early in the morning of April 6, and became a serious issue. It is very likely that this crack may have resulted from the earthquake ground motion. There appears to be artificial structures facing the ocean all around that area, and the surfaces of roads running in the vicinity had long cracks attributable to powerful shaking and soil liquefaction.
The 2011 great off-Tohoku earthquake was an exceptionally gigantic event of M 9.0. The seismic fault plane had an approximate length of 450 kilometers and the source region continued to release seismic waves for about 180 seconds. So, violent tremors lasted for a very long time at every place in the area of strong shaking (see Figure). Although the seismic records at the Fukushima Dai-ichi nuclear power plant have a serious flaw in that they are discontinued at around 130 to 150 seconds after the beginning of the record with an exception for the vertical component in Unit 6, it is estimated from seismic records in the vicinity that severe shaking continued at the plant for about three minutes. It is highly possible that this very long vibration (and especially three violent jolts during the vibration) may have caused damage to the buildings, devices, piping and other facilities of prime importance such as pressure suppression chambers.
The crack on the pit clearly violates a provision in the Revised Guide, which reads that buildings and structures shall be founded on the grounds which have sufficient supporting capacities. This violation directly led to serious contamination of the seawater.
At the Fukushima Dai-ichi nuclear power plant, numerous people are working selflessly under severe conditions to deal with the accident. It must be noted that the possibility of another major tsunami hitting the power plant, now totally defenseless, cannot be ruled out. A large aftershock on the landward side of the Japan trench, the submarine trace of the plate boundary, may cause such a tsunami, but apart from that, the gigantic interplate earthquake on March 11 could possibly induce a great earthquake within the Pacific plate on the outer side of the trench (a region called the outer rise). Actually, in case of the 2006 November great interplate earthquake of M 8.3, off Simushir Island along the Kuril trench, a northeastward extension of the Japan trench, an M 8.1 great earthquake occurred in the Pacific plate on the outer side of the trench around two months after the former. It is important to pay close attention to great earthquakes of this kind, given that they are in the same category as the 1933 Showa Sanriku earthquake of M 8.1 and have a tendency to produce a huge tsunami. (They might be able to be predicted to a certain extent by monitoring seismic activity, but this is uncertain.)
Note: The diagrams demonstrate the three-component acceleration waveforms on the ground surface at K-NET station FKS005 in Haramachi-ku, Minamisoma City, Fukushima Prefecture, around 24 kilometers to the north of the Fukushima Dai-ichi nuclear power plant. K-NET, or the Kyoshin Net, is a network of strong-motion seismographs operated by the National Research Institute for Earth Science and Disaster Prevention (NIED). For comparison, the seismograms of the 2005 off-Miyagi earthquake of M 7.2 at the same station are shown in gray by the same scale of both horizontal (time) and vertical (amplitude) axes. Diagrams courtesy of Dr. Harada Tomoya.
The author had pointed out that large intra-slab earthquakes within the subducted Pacific plate descending beneath the Tohoku district from the Japan trench (called a slab) became more likely depending on depth and other factors. The M 7.1 earthquake which took place off the coast of Miyagi Prefecture late at night on April 7, causing trouble at the Higashidori and Onagawa nuclear power plants of the Tohoku Electric Power Co., Inc., was just an intra-slab earthquake. Quakes of this kind may also occur immediately beneath the Fukushima Dai-ichi or Dai-ni nuclear power plants, tending to produce violent tremors. There is no option but to pray intensely that there is no more major earthquake or tsunami which could result in catastrophe of the two nuclear power plants.
Translated from “Fukushima genpatsu shinsai: Dai-shizen ni taisuru mubo-na tatakai-ni yabureta ima, saizen-no sengo-shori wo isoge,” Kagaku, May 2011, pp. 0411-0416, ?2011 by Ishibashi Katsuhiko. Reprinted by permission of the author c/o Iwanami Shoten, Publishers.