Nuclear fusion, a theoretical way of harnessing power by fusing atoms which is still under development, may one day provide a cleaner alternative to the world's energy problem.
Meanwhile, research into fusion power (in which energy is generated by fusing hydrogen atoms together at very high temperatures) has left behind a different kind of debris: a trail of experimental reactors, none of which has yet reached the break-even point where the amount of energy that comes out exceeds the amount put in.