Research On Optimization And Modification Of Zr-based Alloys For Tritium Adsorption In Molten Salt Reactor Off-gas

The Zr Co and Zr V₂alloys of Zr-based alloys have great potential to be used for the adsorption and storage of tritium in the off-gas of Thorium Molten Salt Reactor.In order to solve the problems of Zr Co alloys among Zr-based alloys which are prone to hydrogen disproportionation reactions during high temperature desorption of hydrogen isotopes and of Zr V₂alloys which are susceptible to O₂poisoning,this study characterised the alloy morphology and structure,tested the comprehensive hydrogen storage properties and carried out a First-Principles study,the main results are as follows.（1）A non-stoichiometric Zr Co_x（x=0.9,1.0,1.1）alloy was prepared using vacuum arc melting.Characterization showed the presence of a readily disproportionated hydrogen-absorbing phase Zr₂Co for Zr Co_0.9and a non-disproportionated nor hydrogen-absorbing phase Zr Co₂for Zr Co_1.1,with the secondary phases causing changes in alloy properties.At 250°C,the hydrogen storage capacity H/M=2.23 for Zr Co_0.9,H/M=2.24 for Zr Co_1.0and H/M=2.01 for Zr Co_1.1.The hydrogen absorption rates were determined as Zr Co_1.1>Zr Co_0.9>Zr Co_1.0.An excess of B-side elements enhanced the disproportionation resistance of the alloy,with the disproportionation ratios in this order Zr Co_1.1>Zr Co_1.0>Zr Co_0.9,and the disproportionation ratio of Zr Co_1.1decreased by 23%compared to Zr Co_0.9at 550°C.The disproportionation kinetic fitting revealed that the alloy disproportionation process followed a heterogeneous two-dimensional nucleation mode.（2）Optimisation of oxygen atom adsorption on the Zr V₂（100）surface showed that the bridge site was the preferential adsorption site.On this basis the oxygen atom adsorption behaviour was investigated by surface modification treatment with Pd,Hf and Ti,from which it was revealed that the Pd substitution modific_Ia_Ition has the best anti-toxicity properties.By studying the electronic structure before and after doping,it was found that the electronic interactions between the oxygen atoms and the surface atoms were weakened and the overall energy was increased after the doping of Hf with Pd.（3）Zr V₂,Zr_0.9Hf_0.1V₂,Zr V_1.8M_0.2（M=Pd,Nb）alloys were prepared using vacuum arc melting.After high temperature heat treatment at 1000°C for 168h,the annealed Zr V₂ alloy showed significantly improved phase homogeneity and hydrogen absorption properties compared to the as-cast state,demonstrating that the annealing treatment optimises the properties of the Zr-V alloy.After hydrogen absorption kinetics and PCT testing of the annealed alloys,the doping modification of Zr V_1.8Pd_0.2 and Zr_0.9Hf_0.1V₂ showed the most prominent improvement in hydrogen absorption rate and hydrogen storage capacity.Following this,a 0.5vol%O₂ hydrogen-oxygen mixture poisoning kinetic experiment at 25°C was carried out,with80%loss of hydrogen storage capacity for Zr V₂,30%loss for Zr_0.9Hf_0.1V₂ and 20%loss for Zr V_1.8Pd_0.2,verifying experimentally that Zr V_1.8Pd_0.2 has good resistance to poisoning compared to Zr V₂ and Zr_0.9Hf_0.1V₂.