Tritium trapping by metal oxides in radioactive wastes

Abstract

International audienceITER (International Tokamak Experimental Reactor) is a fusion machine which should demonstrate scientific and technological feasibility of fusion energy by means of D-T fusion reaction. Therefore, most of the solid radioactive waste produced during operation and dismantling phase (around 34 000 tons) will result not only from activation by 14 MeV neutrons, but also from contamination by tritium. One of the main issues in tritiated waste management is the confinement of tritium which presents a good ability to diffusion. One of the solutions is to trap the tritium directly in waste drums. In containers tritium is under gaseous form (HT and T$_2$), tritiated water vapor (HTO and T$_2$O) and organic bounded tritium species (OBT). As a hydrogen isotope, HT and T2 conversion is possible thanks to a reaction with a mix of metal oxides MnO$_2$ and Ag$_2$O, which can be used for hydrogen hazards mitigation. Associated to a molecular sieve, trapping of tritiated hydrogen and water is workable. This paper will describe a methodology to develop a trapper. An experimental study will enable to test different formulation of oxidation powders (with or without catalyser Pt, Pd, Cu, salts). It will enable to obtain the most efficient mix of powder to convert tritiated hydrogen in tritiated water. After determined reaction kinetics with the best trapper, tests will be focused on tritiated water adsorption phenomenon. Then, a modelling part will aim to analyse the influence of trapper on diffusion of tritiated hydrogen outside radioactive waste drum, with obtaining firstly tritium release rate without trapper and secondly this rate for tritiated waste drum with trapper inside