Lots actually, the way it is fueled, completely different (as in you don't re-fuel it you replace it) so all of the re-fueling infrastructure is not needed. The

Lots actually, the way it is fueled, completely different (as in you don't re-fuel it you replace it) so all of the re-fueling infrastructure is not needed. They replace water (low pressure or high pressure) with helium which gives them two benefits, one it carries more heat and two it doesn't become a high explosive[1] when exposed to extreme temperature. Another benefit of helium is that if it leaks from the system, it carries no fission byproducts(like Cesium) in solution and has no radioactive isotopes with half lives of more than a second. 6-Helium has a half life of .8 seconds and emits a beta particle. So pretty much all different :-)