The Fukushima nuclear power plant was designed, as are most buildings in Japan, to withstand a huge earthquake. In a sense, it did.  The tectonic shock that struck the country last week was much more powerful than any in recent memory and yet the tremor itself did not cause an atomic calamity. It was the following tsunami that overwhelmed power supplies at Fukushima, resulting in overheating, fire and panic at the prospect of radiation leaking into the atmosphere.  Which particular facet of a natural disaster broke Fukushima hardly matters to those engineers bravely struggling to bring the reactor under control. Nor does quibbling over causes comfort those people who have had to flee their homes. What good is a nuclear power plant on a coastal fault line that survives earthquakes but not tsunamis? The point is worth making, however, to underline quite how unusual the seismic event that devastated Japan was and so to put in some perspective the problems at Fukushima.  That perspective is vital because the plant's problems are already having an impact on debate over the long-term viability of civil nuclear energy.  It is 25 years since a fire at Chernobyl sent a plume of radioactive smoke into the skies over Europe. It took many years, a concerted public relations effort by the nuclear industry and advances in safety technology for