By using different fuels. The fuel we currently use (enriched uranium) was chosen because we could also use it to build weapons. A different fuel (i.e. thorium, etc) could be used that couldn't be used in making weapons.
This question aside, I feel states can not resist the temptation to get nuclear bomb technology: It's a great equalizer for power. Looking at how North Korea was able to repeatedly get U.S to the bargaining table, I think none of the nuclear powered country would want any other country on Earth to gain such technology.