Neutron activation of impurity seeding gases within a DEMO environment

Abstract In preparation for the design of a future tritium-handling plant for the DEMO fusion reactor, a study was undertaken to consider the activation of gases, in addition to those used as fuel, which are to be injected into DEMO for the purpose of reducing damage to the divertor. Likely impurity gases were identified as nitrogen, neon, argon, krypton and xenon, with no clear consensus as to which were preferred, and in what quantities these would be injected. Modelling with the FISPACT-II code, using the TENDL-2014 libraries as input, was performed to determine the products arising from their activation by the neutron flux expected at the DEMO first wall. The subsequent evolution of the progeny was investigated, along with a variation in the activation time. Results indicate a variety of progeny are produced, most of which are short lived. However, the gamma emission from some progeny such as argon-41 from argon injection, from some metastable states and other isotopes of krypton and bromine following krypton injection, and from some metastable states of xenon following injection of xenon, could potentially cause concern.