The Japanese reactor is a steam generator. It must first operate at high temperatures to generate steam hot enough to drive generator turbines. But the newer technology GT-MHR reactor core ONLY has to operate at much lower temperatures because it uses heated helium (rather than steam) to drive a turbine generator.What kills me is all the bunny lovers who would like people to think that any new reactors that will be built would use the some 50 year old designs that we operate now. http://gt-mhr.ga.com/
Because of the helium, the core of a GT-MHR can operate at much lower temperatures, AND because of that, the core won't overheat DUE to a coolant loss (from a natural disaster), create a meltdown, and then pollute.
When coolant is lost, a GT-MHR core is already at a much lower temperature than is a traditional steam generating reactor core. The GT-MHR reactor WILL cool down without the aid of coolant. A Steam reactor must have water to help it cool down long after it has been shutdown.The GT-MHR's decay heat will not cause a meltdown even if the coolant is lost. The reactor's low power density and geometry assure that decay heat will be dissipated passively by conduction and radiation without ever reaching a temperature that can threaten the integrity of the ceramically-coated fuel particles even under the most severe accident conditions.