The answer to that question is being sought by the American people.  The troubled Fukushima reactors are GE Mark 1 BWR designs.  These reactor cores stay hot for days if not weeks following an emergency.  Their massive plumbing networks are their Achilles heel during a massive earthquake.  The reactors work by creating heat and superheating the surrounding water.  That water is then turned into steam and turns a massive turbine under high pressure.  It is then cooled and returned.  All of the plumbing is meant to contain these massive pressures and heat.  The huge external stresses caused by the earthquake and tsunami have severely damaged the system.  In a later post we will discuss the newer more inherently safer technologies.  Designs like the Traveling Wave Reactor, Pebble Bed Reactor, and a handful of new mini reactor designs.  For now all we can do is pray for Japan.