Statement calling for a review of the volcanic impact assessment in the new regulatory standards for the restart of nuclear power plants in light of the Tonga eruption

February 15, 2022

1. Occurrence of the Funga-Tonga-Hunga Ha’apai eruption

　　On January 15, 2022, a large-scale eruption occurred at the submarine volcano on the island of Hunga Tonga-Hunga Ha’apai, located about 65 km north of Nuku’alofa (Tongatapu Island), the capital of the Kingdom of Tonga (hereinafter referred to as the “HTHH eruption”). The plume rose to an altitude of 15 to 6 km and formed an umbrella-shaped plume with a diameter of about 500 km (radius of about 250 km) in just a few tens of minutes. The aerosol is thought to have reached the stratosphere.

　　The shock wave (aerial vibration) from the HTHH eruption traveled around the globe, and it is said that the sound of the explosion was heard even in New Zealand, more than 2,000 km away.

　　A tsunami of up to 1.2 meters in height was also observed in Japan (Kominato, Amami City), causing damage such as the capsizing of fishing boats. The Tongan government announced that the tsunami reached a maximum height of 15 meters. These tsunamis are believed to have been events that cannot be explained by conventional tsunami mechanisms, and while some believe they were caused by aerial vibration, others point to changes in water levels caused by the caldera sinking.

　　Furthermore, discoloration of the seawater, thought to be caused by volcanic activity, has been confirmed to have spread as far as 300 km, and experts in Japan and abroad are not sure if this is the end of the eruption.

　　Based on the scale of the plume, it is believed that the eruption may have released about 10 km3 of volcanic material, about the same level as the 1991 eruption of Pinatubo volcano in the Philippines, which also caused global cooling, and the volcanic explosion index (VEI) is thought to be around 5-6.

2. Eruption that was not predicted or warned in advance

　　The islands of Hunga Tonga and Hunga Ha’apai are both separate islands at the edge of a huge submarine caldera crater (1,800 m high and 20 km wide), and although they are known to have been active about 1,000 years ago, they were quiet volcanoes until a major eruption occurred in 2009.

　　Then another eruption occurred in 2014-2015, and the land was united to form the island of Hunga Tonga-Funga Ha’apai (HTHH). However, although there were some who pointed out the possibility of activity, the island was basically considered to be normally quite quiet and so on.

　　In December 2021, prior to the HTHH eruption, HTHH erupted again. In December 2021, prior to the HTHH eruption, HTHH erupted again, this time to a height of about 16 km, but experts who visited the site afterwards said that they saw nothing unusual.

　　The HTHH eruption was not predicted or warned of such a large-scale eruption.

3. There are many things that we do not understand with our current knowledge 　　

The cause of the tsunami that struck Japan is still unclear, and its mechanism has not been elucidated. 　　Although it is comparable to the Pinatubo eruption, its behavior is very different from that of the Pinatubo eruption. Yujiro Suzuki, associate professor of volcanic physics at the Earthquake Research Institute of the University of Tokyo, analyzed the spread of the plume based on images taken by satellites and compared it to simulations of the volume of plumes from Pinatubo and other volcanoes, estimating that the volume of plumes per second is about three times that of Pinatubo. Associate Professor Suzuki said, “I’ve never seen a plume expand at such a rate before, and I’m very surprised.” I am very surprised. On the other hand, the amount of volcanic ash and pumice, as well as sulfur dioxide, which is considered to be the cause of climate change, is low, and it is predicted that climate change will be avoided, but it is not clear why the amount of sulfur dioxide is low. 　　

The HTHH eruption is also a submarine volcano, and there is much less knowledge about it than about land volcanoes, so there is much we do not know. Janine Krippner, a volcanologist at the Smithsonian Institution in the U.S., says, “At this point, we have far more questions than we know,” but in any case, with the current level of science and technology, it is impossible to accurately understand all the events and phenomena associated with volcanic eruptions. In any case, with the current level of science and technology, it is impossible to accurately understand all the events and phenomena associated with volcanic eruptions, and it has become clear once again that predicting volcanic events is extremely difficult.

4. Similarities between Japan and Tonga, and the possibility of a large-scale submarine eruption in Japan 　　Although the HTHH eruption is comparable to the Pinatubo eruption, which is said to be the largest eruption in the 20th century, it is not a rare phenomenon, as Japan has experienced many eruptions of a larger scale than this in the past. 　　Japan is the world’s largest volcanic country, with about 7% of all active volcanoes (volcanoes that have erupted within the past 10,000 years), and 111 of them. As an island nation surrounded by the sea on all sides, about one-third of the active volcanoes are located in the Izu-Ogasawara Islands and the Nansei Islands. Professor Yoshiyuki Tatsumi of Kobe University points out the similarities between the geography of Tonga and the Japanese archipelago, especially the Izu-Ogasawara and Mariana Islands, and suggests that eruptions like the HTHH eruption could occur in Japan in the future. 　　It is still fresh in our minds that the August 2021 eruption of Fukutoku Okanoba, a submarine volcano, caused a great deal of pumice to drift to the Japanese archipelago, which caused tension among those involved in nuclear power plants, but this was a much smaller eruption than the HTHH eruption. In recent years, it has become clear that a huge lava dome has formed in the Onikkai Caldera, which had a catastrophic eruption about 7,300 years ago, but this eruption is much larger than the HTHH eruption. There is no other way to say that we do not know.

5. Errors in volcanic impact assessment to date

(1) The HTHH eruption once again demonstrated the limitations of current volcanology and also showed that disasters caused by volcanic events are real and cannot be ignored.

　　However, the volcanic impact assessment conducted by the Nuclear Regulatory Commission (NRC) as part of its determination of compliance with the new regulatory standards has, in effect, been trivialized as if a massive eruption (an eruption in which underground magma erupts to the surface at once, resulting in a massive pyroclastic flow with an eruption volume of more than tens of km3) could not occur. The March 7, 2018 “Basic Concept on ‘Evaluation of Volcanic Activity with Volcanic Events that Cannot be Designed for’ in the Volcanic Impact Assessment Guide for Nuclear Power Plants” (hereinafter referred to as the “Basic Concept on Mega Eruptions”) embodies this concept, and the injustice of this concept was explained by the Liaison Committee in its March 13, 2018 report. However, the Nuclear Regulatory Commission (NRC) has since issued a report on this issue.

　　However, the Nuclear Regulatory Commission (NRC) not only ignored our statement, but also revised the Volcanic Impact Assessment Guide on December 18, 2019, and formally incorporated the “Basic Concept on Massive Eruptions” into the Guide.

(2) The revised Volcanic Impact Assessment Guide acknowledges that the process leading to a major eruption is not fully understood and that a major eruption would cause serious and severe damage to a wide area if it were to occur. The risk is acceptable if (1) the current activity is not considered imminent (non-imminent), and (2) there is no scientifically reasonable concrete evidence for the possibility of a major eruption during the operational period (lack of concrete evidence) (Section 4.1(2)).

　　However, even catastrophic eruptions of VEI 7, which are even larger than giant eruptions, have occurred since prehistoric times, such as the eruptions of Mount Paektu (around 960) and Tambora (1815), and the Volcano Guide, which relies on the scientifically totally meaningless fact of whether there have been any observed cases since prehistoric times in areas around Japan, is wrong in its assumptions.

　　Since the process leading to an eruption has not been fully elucidated, it is difficult to show the imminence of (1) and the concrete evidence for (2), and in effect, the risk of a huge eruption is being ignored (there have been no cases in which the risk of a huge eruption has been considered).

(3) What is more problematic is that the framework seems to exclude even large eruptions that do not lead to large eruptions.

　　The Revised Volcanological Guide states that if a volcano has had a major eruption in the past and the possibility of a major eruption is judged to be sufficiently small, the largest eruption since the last major eruption should be assumed (Section 4.1(3)).

　　For example, Aso Caldera has had four catastrophic eruptions (ejecta volume of over 100 km3) in the past, but the largest eruption since the last catastrophic Aso 4 eruption was the Kusasenrigahama pumice eruption (ejecta volume of about 2 km3), which is not even a huge eruption.

(4) As mentioned above, the HTHH eruption may be a VEI6 class eruption, and we cannot deny the possibility that it will continue to be active and develop into a huge eruption. What we learned from this eruption is that large-scale eruptions can occur in Japan, and therefore we should not ignore the risk of such eruptions, and that there are many things we do not know with the current level of volcanology. Trying to downplay and trivialize the risk of a large-scale eruption is not a “socially accepted idea,” but merely a bias or desire of those who do not want to shut down nuclear power plants. The Nuclear Regulation Authority (NRA), whose mission is to protect the safety of citizens from nuclear disasters, should not be allowed to endanger the lives and bodies of many people living in the vicinity of nuclear power plants over a wide area based on such assumptions and wishes. If there were no nuclear power plants in the vicinity of a volcano, even if an eruption occurred, as in the case of the Pinatubo eruption, recovery and reconstruction would be possible within a few years to a decade. The presence of a nuclear power plant will cause the spread of radioactive materials, making the area around the plant uninhabitable for a long time. Without bringing up the rights of future generations or intergenerational ethics, it is hard to imagine that the law even permits the operation of nuclear power plants without taking such risks into consideration.

(5) Furthermore, in the past volcanic impact assessments, only a cursory assessment of the effects of submarine volcanoes has been made, but the August 2021 eruption of the Fukutoku Okanoba submarine volcano and the recent HTHH eruption have made it clear that there are too many things about the behavior of submarine volcanoes that are not understood by current science. It has become clear that there are too many things we don’t know about the behavior of underwater volcanoes. Rather than ignoring what science does not understand in this regard, it is necessary to thoroughly conduct conservative assessments to ensure the safety of nuclear power plants even in the event of unforeseen events.
6 The Nuclear Regulatory Commission should completely review the method of volcanic impact assessment and other aspects.

　　In this way, the HTHH eruption has shown how the volcanic impact assessment has been based on wrong criteria.

　　The government’s accident investigation report on the Fukushima Daiichi nuclear power plant accident (TEPCO Fukushima Nuclear Accident Independent Investigation and Verification Commission) proposes a shift in risk perception, stating that before the Fukushima Daiichi nuclear accident, “natural phenomena can cause events that exceed the current state of academic knowledge, and the traditional precautionary approach of preparing for such extremely rare events must always be considered in parallel.

　　In other words, the report recommends that “Japan should bear in mind that it is a ‘disaster-prone country’ that has been struck by various natural disasters since ancient times, and humbly confront the threats of the natural world and the scale and time scale of tectonic movements. In the case of accidents and disasters that cause enormous damage over a wide area, such as the accident at the Fukushima Daiichi Nuclear Power Plant, it is necessary to establish a new concept of disaster prevention that requires appropriate safety and disaster prevention measures to be taken regardless of the probability of occurrence, both in government and business” (pp. 412-413 of the Final Report).

　　The current volcano guide clearly contradicts these recommendations. The Nuclear Regulatory Commission (NRC) should take the opportunity of the HTHH eruption to completely review the methods of volcanic impact assessment, etc., based on the conservative assumption that a large-scale eruption will actually occur, correctly taking into account the indefiniteness of science and the limitations of current volcanology.
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February 17, 2022 Posted by dunrenard | Japan | Assessment, Nuclear plants restart, Volcanic impact | Leave a comment