All of the world’s existing commercial nuclear power plants and those under construction are water-cooled reactors. These plants were expected to operate for 30-40 years. Today it is expected that many plants will operate for 60 years. There are operating demonstration fast reactors and high-temperature reactors; however, it will be several decades before signiŒcant numbers of these reactors could be built. If any signiŒcant quantities of nuclear hydrogen are produced in the next several decades, it will be from water-cooled reactors.