Tritium is produced in nuclear reactors when heavy water absorbs neutron radiation and when uranium is used as reactor fuel and also tritium is produced in nuclear reactors by neutron activation of lithium-6.
This is possible with neutrons of any energy and is an exothermic reaction yielding 4.8 MeV. In comparison, the fusion of deuterium with tritium releases about 17.6 MeV of energy.
