A silly thing about light water nuclear reactors is that half a percent of energy as mass (E = mc2) in nuclear fuel is used. This is one example of an advanced reactor that uses all the energy. Energy and fission products are what are left after nuclear fission. The latter are lighter and far less long lived than heavier radioactive elements. Hundreds of years not many thousands. Remove these as waste with AIROX dry separation and recycle actinides in a closed nuclear fuel cycle.
This is General Atomics. They have built helium cooled reactors. They have commercial silicon carbide fuel rods for light water reactors. To prevent explosions like at Chernobyl and Fukushima. This advanced design can’t melt down or explode.
Factory built – runs for 30 years without refueling.