Water decomposes above 3000 C

First, fusion has 0 theoretical economic potential, but there is some potential for energy gains from 2250^^ + steam. Water deconstructs above this temperature into powerful HHO gas, that when ignited gains another 2500^^ that will chain react with higher pressure steam to make the steam even hotter/higher pressure. Minor problem of melting all known turbine material, is avoidable through just higher volume of pressured steam.