Tritium permeation in EUROFER97 steel in EXOTIC-9/1 irradiation experiment

Abstract

This paper presents the results of the tritium permeation study in EUROFER97 carried out within the EXOTIC (EXtraction Of Tritium In Ceramics) irradiation experiment. In the EXOTIC 9/1 experiment, a pebble bed assembly containing Lithium Titanate (Li2TiO3) pebbles is irradiated for 300days in the High Flux Reactor (HFR), in the temperature range between 340 and 580 °C, reaching a lithium burn up of 3.5% and 1.2 dpa of damage in steel. The primary objective of this experiment was to measure the in-pile tritium release characteristics of Li2TiO3 pebbles. Additionally tritium permeation through the EUROFER97 pebble bed wall was measured on line. The permeation of tritium was studied at steady state conditions, during temperature transients, and at different hydrogen concentrations in the helium purge gas flow.The model used in the analysis of the experimental data which account for co-permeation of tritium and hydrogen is presented. It has been demonstrated that the permeation of tritium under experiment conditions proceeds in the diffusion limited regime. From the analysis of the experimental data the permeability and diffusivity of tritium in EUROFER97 is determined.