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Is Meteorite-Preparedness just a lot of Hype?

Published on Mar.1 ,2013 : The Denki shinbun(The Electric Daily News)
Shojiro Matsuura
Chairman of JANSI

The Chebarkul meteorite that fell to earth near Chelyabinsk, Russia in the morning of this past February 15 brought with it a very difficult question for those of us in Japan whose aim is to continuously improve the assurance of nuclear safety. Motorists who were driving to work captured the magnificent cosmic pageant of the meteorite falling through the sky and the flash of the fireball with the onboard cameras they had in their cars. However, when it dawns on you that "Surely, there are a number of nuclear power facilities in the Chelyabinsk area!", it sends a cold chill up your spine. Most probably, a great number of persons related to the nuclear industry must have felt this chill.

The second anniversary of the catastrophic giant tsunami that touched off the Fukushima nuclear accident is just around the corner. It was this accident that sparked the need for structural reform and paradigm shift in the ideology of maintaining safety in nuclear power stations not only here in Japan, but around the world.

The aim of maintaining nuclear safety is to protect people and the environment against the risks of radiation exposure that comes with the territory of utilizing nuclear energy, whose foundation is constructed on the idea of defense in depth, and executed accordingly. In the past, the major accidents at TMI Unit 2 and Chernobyl Unit 4 exerted pressure for paradigm shifts, for which tough interactions were attempted. In the case of the former, even though the core melted down, there was no widespread diffusion of radioactive materials into the environment of the surrounding area. In the latter, an explosion occurred at the core causing a huge conflagration, which resulted in spreading a large amount of radioactive material into the environment. Although the structure of those two reactors differed radically, and so did the cause of the accidents, the accidents shared the common factors that the concerned parties had not anticipated what eventually happened, and the accidents were caused by internal event inside the reactor.

The American Society of Mechanical Engineers (ASME) analyzed the Fukushima reactor accident based on Japanese accident investigation reports and issued their own report entitled "Forging a New Nuclear Safety Construct," summing up the event, "The Fukushima Dai-ichi units are the first nuclear reactors in the world in the fifty-plus years of nuclear plant operation to sustain core degradation due to catastrophic external events, the first to involve simultaneous multiple unit failures, and the first light water reactors to release large amounts of radioactivity to the environment," and numerous other specialized academic societies present the same basic argument. Furthermore, there is worldwide recognition that "With present day LWR technology and adequate preparations and operation of the facilities, it should have been possible to cope with catastrophic external phenomena such as that experienced at the Fukushima reactors. However, future research into dealing with exceedingly rare and colossal external phenomena is absolutely essential."

In other words, the gist of the new nuclear safety assurance paradigm is how to prepare for responding to major accidents caused by catastrophic external phenomena. In the working draft of "New Safety Standards" now open to public comment recently announced by Nuclear Regulatory Authority of Japan, there is strong awareness of this point, and severe accident countermeasures especially emphasize this.

And then, the meteorite fell to earth. Meteorite strikes are not particularly rare. However, since nearly all of the meteorites burn out during the fall, they rarely hit the ground or pose any special danger to human society. The meteorite that fell just a few days ago is said to be the first case of a meteorite causing widespread injury and damage to buildings. Nonetheless, there are confirmed cases throughout the earth's history when meteorite strikes have had profound effects. It is believed that a giant meteorite fell on the Yucatan Peninsula in Mexico some 65 million years ago, leading to the extinction of dinosaurs and many other species of living animals. It is also said that this kind of event has happened roughly once in every 70 million years. This sort of phenomenon is a very rare occurrence, but it did really happen in the past.

Up until now, meteorite strikes have never been considered in terms of nuclear safety assurance. Neither are meteorite strikes considered in the New Safety Standards (tentative). I do not think considerations are needed any time soon. However, when one sees the actual damage, risk assessment at the very least needs to be conducted. This is a matter for worldwide concern, so shouldn't specialists from all over the world be consulted and attempts made to perform risk assessment of meteorite strikes in the utilization of nuclear energy? This might be needless anxiety. Still, such attempts should be meaningful in redefining nuclear safety standards.

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