A 9.0 magnitude earthquake is equal to about 450 megatons of TNT being set off underground. Due to the situation at the Daiichi nuclear plant near in Sendai Japan there is much talk of how nuclear plants should not be built in earthquake zones. The purpose of this report is to point out the utter futility of trying to avoid such a incident though site selection alone because an event such as this could happen anywhere on Earth. Anywhere that could experience a near hit from an asteroid of sufficient size.
The impact of a asteroid may sound far fetched however may be every bit as likely as a earthquake of the magnitude which struck off the coast of Japan. Just to give some perspective of how likely this is in easily understood terms let us consider two real historical asteroid impacts.
The Tunguska event which hit Siberia over 100 years ago was between 5 and 30 megatons. An event like this one could happen once every 400 years or less.
The impact that killed the dinosaurs and many other whole families of animals 65 million years ago was about 10000000 megatons. An event like this happens very very rarely. Obviously if something like this one happens we will have bigger worries than a nuclear power plant!
Based on those numbers I would estimate that an impact that could cause the equivalent of a 9.0 earthquake would occur every 1000 years or so. However any astronomer will tell you that we do not know the whereabouts of the vast majority of dangerous asteroids. It’s very likely that the planet has been hit by such asteroids...far from any populated area... and the first we knew about them was there seismic effect at distant seismographs. Most of these would impact in the oceans and may not even be noticed unless we are looking in the right place at the right time. There would be very little to distinguish such an event from an earthquake if no impact crater were present, and the initial fireball had faded.
While there is no evidence that the currently unfolding event was caused by such an asteroid impact the truth is it could have been. The scary conclusion is that while siting a nuclear plant far from a earthquake zone will reduce the risk of catastrophe it will not eliminate it.
What can we do?
There exist several new designs for nuclear power plants which would be much much more safe than the design which is about to fail. One design in particular would, in this same situation be much safer than the boiling water reactor. The design I like is called the pebble bed reactor.
In such a reactor the heat from the core which contains pebbles of radioactive material is conducted by an inert gas. Such a reactor holds the promise of being fail safe. They would be cooled by an inert and non flammable gas. This means that all supporting machinery could fail and the reactor would not melt down. The reactor would attain thermal equilibrium and stay at temperature without any human intervention for the lifetime of it’s fuel supply.
Such a reactor built underground would be expensive...but utterly fool proof if correctly designed and constructed.
There is no need to abandon nuclear power. Humanity as a whole just needs to stop being cheap about nuclear safety. Older plants such as the 1960’s design used in Japan need to be decommissioned and replaced with newer and better reactors. However natural disaster can undo even the safest design...sometimes crap just happens.