Question

Which is safer: fission or fusion?

Answer 1

Fusion on several counts. The main downside is that we have not yet produced a practical fusion reactor for everyday use.

Explanation:

Fission can result in runaway nuclear reactions, resulting in meltdown and release of a wide variety of heavy radioactive isotopes. Fission reactors also pose quite a hefty problem of disposal of toxic wastes.

Fusion could also result in catastrophic reactions, but our attempts at fusion reactors have so far been fairly safe. In addition note that the results of fusion reactions are invariably lighter elements that pose much less threat of environmental pollution.