Tritium Permeation Through Metals Under Steam Conditions

Abstract

In fusion reactor power plants the permeation of tritium from the coolant into the steam system must be minimized to prevent release of tritium to the environment. A very promising approach to this requirement is construction of the heat exchanger from a material that will be oxidized by the steam to form an almost impermeable oxide layer on the construction material. Studies of the permeation through nickel have shown that protium permeabilities are 1.6 and 1.5 times greater than tritium permeabilities at 1000 and 700°K, respectively. Studies of the effects of in situ steam oxidation to reduce tritium permeation rates through Incoloy 800 have shown that the tritium permeabilities of some steam generator materials will probably be reduced by the formation of oxide coatings. The effects of severe thermal shock on the oxide coating on Incoloy 800 were observed to destroy the effectiveness of the oxide to impede permeation whereas mild temperature cycling had no effect on the permeation rates.