Tritium inventory and related environmental impact of fusion structural materials

Tritium is a radioactive isotope (half-life = 12.24 yr) present both in fusion and in fission reactors. It is a weak beta emitter, very noxious for humans when inhaled or ingested. Tritium is a fuel for fusion reactors: D + T → n + He and it is bred in the blanket through the reactions of the fusion neutrons with the isotopes of lithium. Tritium is also produced in fission reactors through ternary fission and activation, but at a much lesser extent than in fusion devices. The tritium production rate in fission reactors varies from ∼2 g/yr for pressurized water reactors and boiling water reactors to ∼60 g/yr for heavy-water reactors (referred to 1 GW electric). Being a hydrogen isotope, tritium has the great capability of being retained in all the reactor structures, and the tritium inventory depends both on the reactor design and the physical properties of the materials. This paper evaluates the impact of the selection of structural materials for the first wall and blanket in fusion reactors on the global tritium inventory. The potential radiological impact of a hypothetical accidental release to the environment of equal quantities of tritiated materials is estimated and the results compared with those for activated fusion materials and fission product