World is ignoring most important lesson from Fukushima nuclear disaster

Fukushima's most important lesson is this:?Probability theory (that disaster is unlikely) failed us. If you have made assumptions, you are not prepared.?Nuclear power plants should have multiple, reliable ways to cool reactors.?Any nuclear plant that doesn't heed this lesson is inviting disaster.

A year has now passed since the complete core meltdown of three boiling water reactors at Tokyo Electric Power Company?s Fukushima No.1 plant. Because of the limited information issued by the Japanese government ? and its insistence that the disaster was only a result of the unanticipated magnitude of the earthquake and tsunami ? the world does not know what really happened and will thus draw the wrong lessons.

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The most critical lesson for the global nuclear industry to learn, since most plants around the world do not face tsunami or earthquake risks, is that no one imagined that the external electricity supply from outside the plant that would cool the reactors could be disrupted. That assumption, just like the assumption that a natural event of the size that took place was unlikely, was based on ?probability theory? taught to all nuclear engineers. It is the basis ? wrongly ? for telling the public that nuclear power generation is ?safe.?

As a nuclear core designer who obtained my doctorate from Massachusetts Institute of Technology in Nuclear Engineering, I volunteered to look into the situation at Fukushima No.1 in June of 2011. Goushi Hosono, Japan?s minister of Nuclear Power and Environment, personally granted me access to the information and personnel who were directly involved in the containment operations of the post-disaster nuclear plants.

My now completed investigation shows that the Fukushima accident could have been avoided if the plant had the capacity for electricity generation of any form along with the appropriate heat sink (a supply of water to cool down reactor rods). Despite the ?unexpectedly high? tsunami that caused the accident, two reactors, Nos. 5 and 6, remained intact, though they were damaged to the same extent as the other four reactors by the earthquakes and tsunami. The difference was that they had an additional source of electricity beyond links to the outside grid through an air-cooled emergency diesel engine.

The most important lesson of Fukushima No.1 plant, therefore, is that we should have a multiplicity of means to provide a continuous electric supply and heat sinks. This is not the same as ?You should not put all the eggs in one basket.? We should have eggs and apples in a few different baskets.

If a country or company wants to operate a nuclear reactor, it should not assume anything about potential disasters ? be they earthquakes, tsunamis, terrorist attacks, or a plane crash. No matter what happens, the reactor must be brought to cold shutdown, which requires electricity and heat sinks. It is a pretty simple principle.

There is a more general lesson for all operating nuclear facilities: If you have made assumptions, then you are not prepared.

All the nuclear reactors in the world have been designed by probability assumptions, originally proposed by Prof. Norman Rasmussen of MIT. It is a scientific way of expressing what the public will accept.

For example, what is the probability of a plane crushing into Yankee Stadium with a full audience during the World Series? This can be calculated with certain assumptions, and, the theory goes, that ?level of probability of accidents? is something people tacitly accept because it is very unlikely to happen. The same principle was followed at Fukushima: Assumptions were made about possible causes of nuclear plant accidents, and engineering precautions were made accordingly so that ?the reactor is safe.?

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