But unlike what happens in solar fusion—which uses ordinary hydrogen—Earth-bound fusion reactors that burn neutron-rich isotopes have byproducts that are anything but harmless: Energetic neutron streams comprise 80 percent of the fusion energy output of deuterium-tritium reactions and 35 percent of deuterium-deuterium reactions.

via Fusion Power Reactors; 7 Downsides, False Promises, And Drawbacks, Fusion Energy Is A Failed Experiment With Only A Dead End Future Plus Extinction For Humanity Ahead, Leads To Fusion Bomb Technology And Proliferation | A Green Road Journal