It’s both access to abundant energy and far higher efficiency in producing energy. Fusion is more energy-dense and efficient than fission because it converts a larger fraction of its fuel’s mass into energy. This comes down to the mass per nucleon curve which acts like an energy valley. In fission, heavy elements like uranium split into lighter ones, moving slightly downhill on the curve and converting about 0.1% of mass into energy. In fusion, light nuclei like hydrogen isotopes combine to form helium, which is much farther down the valley wall. This steeper drop allows fusion to convert up to 0.7% of mass into energy. So, gram for gram, fusion fuel can release roughly seven times more energy than fission fuel.
It’s both access to abundant energy and far higher efficiency in producing energy. Fusion is more energy-dense and efficient than fission because it converts a larger fraction of its fuel’s mass into energy. This comes down to the mass per nucleon curve which acts like an energy valley. In fission, heavy elements like uranium split into lighter ones, moving slightly downhill on the curve and converting about 0.1% of mass into energy. In fusion, light nuclei like hydrogen isotopes combine to form helium, which is much farther down the valley wall. This steeper drop allows fusion to convert up to 0.7% of mass into energy. So, gram for gram, fusion fuel can release roughly seven times more energy than fission fuel.
https://www.nsta.org/blog/focus-physics-how-e-mc2-helps-us-understand-nuclear-fission-and-fusion