In a "nation dotted with volcanoes", do not forget the risks of volcanoes

 January 22, 2014

As I See It: Include risks of major volcanic eruptions in nuclear reactor safety assessment

http://mainichi.jp/english/english/perspectives/news/20140122p2a00m0na007000c.html

The risks of earthquakes and tsunami causing nuclear disasters have garnered much attention among experts and the public, but I feel a grave need to raise awareness on how much greater a risk a massive volcanic eruption poses on nuclear reactors in Japan.

Volcano experts surveyed for a Mainichi Shimbun article published last December said they were most concerned with the impact of a major volcanic eruption on Kyushu Electric Power Co.'s Sendai Nuclear Power Plant, located in Kagoshima Prefecture, followed by Hokkaido Electric Power Co.'s Tomari Nuclear Power Plant in Hokkaido.

Some 10 years ago, a volcanologist told me that pyroclastic sediment was commonly found in the surrounding areas of both Sendai and Tomari nuclear power stations. I was working at the Mainichi Shimbun's Shimabara Local Bureau in Nagasaki Prefecture at the time, and had been learning about earthquakes and volcanoes through my coverage of the eruption of Mount Unzen-Fugendake that began in 1990.

Consisting of high-temperature substances such as lava and volcanic ash, pyroclastic flows spread at rapid speeds and are some of the most terrifying phenomena resulting from volcanic eruptions. In 1991, a Mainichi Shimbun photographer and 42 others were killed by pyroclastic currents from Mount Unzen-Fugendake.

In volcanology terms, however, the Mount Unzen-Fugendake eruptions are considered minor. Pyroclastic currents from a massive eruption would be beyond comparison.

Massive eruptions, which have occurred in Japan about once every 6,000 to 10,000 years, cause pyroclastic flows that can bury an area within several dozen to over 100 kilometers of the volcano, and create calderas measuring over 10 kilometers in diameter. Volcanic ash from a massive eruption can cover the entire Japanese archipelago, or even parts of the rest of the world.

Take, for example, the major pyroclastic currents produced by Kumamoto Prefecture's Mount Aso about 90,000 years ago. Not only did they burn down the northern half of Kyushu, but they also traveled across the ocean to what are now Yamaguchi and Ehime prefectures. The major pyroclastic flows caused by Kagoshima Prefecture's Mount Aira 26,000 to 29,000 years ago completely destroyed southern Kyushu. Such massive eruptions are particularly common in Kyushu and Hokkaido.

What would happen if a major volcanic eruption were to occur in Japan today, and our nuclear reactors became engulfed in pyroclastic currents?

Nuclear power plants and their surrounding areas would be buried under volcanic ash, making it impossible to control nuclear reactors for long periods of time. Even if radioactive materials were to leak from the reactors, we would not be able to reach the facilities to do anything about it. It would put the very survival of the country at risk.

Is this an exaggerated scenario? The last massive volcanic eruption took place some 7,300 years ago in what is now Kagoshima Prefecture. Based on the average frequency of such eruptions, it wouldn't be surprising if one took place at any time now. The ongoing disaster at the Fukushima No. 1 Nuclear Power Plant was triggered by an earthquake and tsunami said to be of a magnitude seen once every 1,000 years. Then is a one-tenth to one-sixth probability that a massive volcanic eruption could occur small enough to ignore?

In the two-plus years that I have been on the Kagoshima prefectural administration beat since October 2011, the reactivation of the Sendai Nuclear Power Plant has been a major cause of the central prefectural government.

With the risks that major eruptions pose on nuclear power plants always on my mind, I was relieved when such risks were incorporated into the Nuclear Regulation Authority (NRA)'s new safety standards for nuclear reactors. That sense of relief quickly turned into disappointment once the NRA safety assessments began. As it turns out, the NRA is extremely thorough when it comes to quake-related assessment items, but it easily accepted Kyushu Electric Power Co.'s report on the Sendai plant that "an eruption at a nearby volcano would not have any impact on the nuclear power plant." Meanwhile, the power plant is surrounded by the most calderas -- in other words, traces left by massive eruptions -- among all nuclear power plants in Japan.

In some ways, it's understandable. The NRA's deputy commissioner, Kunihiko Shimazaki, who is in charge of the relevant portion of the assessments, is a seismologist, not a volcanologist. And perhaps most significantly, the temporal axis on which the earth exists and the concept of time in which humans function are so dramatically disparate. The dozens of years that a nuclear reactor is in operation is a mere blink of an eye for the planet. Our scientific knowledge and technology cannot yet tell us if a massive earthquake will occur in that time.

Last year, we surveyed volcanologists nationwide on the risks of individual nuclear power plants and provided readers with statistical results because we believed such information would inform how we think about nuclear policy. In addition to answering our questions, the experts offered a range of valuable comments, which could be classified into the following:

1),No massive volcanic eruptions will occur in the time frame in which nuclear reactors are online.

2),There is a small but worrisome possibility that a massive eruption will occur.

3),Some individual nuclear plants face unacceptable risk.

4),There is a limit to what science can tell us, and a social/political decision should be made based on a society-wide deliberation comparing the risks and merits.

I agree with comment No. 4. Seeing as volcano experts vary so widely in their views, the NRA should not rush to any conclusions.

It's not too late. The NRA should establish a subcommittee within the organization comprising volcanologists from Japan and abroad to publicly discuss the risks posed by a major volcanic eruption on individual nuclear plants. The deliberations should include the possibility of not reactivating reactors if they are at "unacceptable risk." Only then can we, as a nation dotted with volcanoes, claim to the world that our safety assessment procedures are sufficient. (By Taro Yamasaki, Kagoshima Bureau)

January 22, 2014(Mainichi Japan)