Study On Hydrogen Permeation Behavior In Fusion Blanket Structural Material

The raw materials of the fusion reactor,deuterium and tritum,have small radius of atom,are easy to permeate through the fusion blanket structural material.Which will not only cause fuel loss,but also affect the safety and stability of the fusion reactor.Thus evaluating the hydrogen isotope permeability of structural materials and studying the hydrogen permeation behavior of structural materials have important scientific significance and practical value for the research and development of structural materials.Low activation ferritic/martensitic?RAFM?steel and oxide dispersion strengthened?ODS?steel are main candidate structural materials for fusion reactors.In this paper,electrochemical hydrogen permeation measurement technology was used to study the hydrogen permeation behavior in super-clean low-activation martensite?SCRAM?steel and ODS steel with N addition.Besides,the hydrogen atom adsorption process on different crystal orientation of TiN and VN were researched based on the first principle.Finally,for the problem of narrow test temperature range of electrochemical hydrogen permeation test,a preliminary exploration of organic electrolyte solution to be used to replace traditional aqueous solution was carried out.The effects of alloying elements Ti and N,different heat treatment processes and permeation temperature on hydrogen permeation behavior of SCRAM steel were investigated.The microstructure characterization results showed that the microstructure of SCRAM steel is tempered martensitic lath with distributed fine precipitates.The particles distributed along the boundary of the martensite lath were mostly M₂₃C₆ phase,and and the finer particles in the lath and the grains were mostly MX particles.Hydrogen permeation results for SCRAM steel with different Ti and N contents indicated that Ti and N can decrease the hydrogen diffusion coefficient of SCRAM steel.Different heat treatment processes were applied for SCRAM steel.The results showed that the intermediate heat treatment process can refine the M₂₃C₆ phase,increase the volume fraction of MX phase but coarsen the martensitic lath.The twice quenching and tempering heat treatment process can not only refine the martensitic lath and M₂₃C₆ phase,but also increase the volume fraction of MX phase,resulting in a decrease of hydrogen diffusivity.Hydrogen permeation test results at different temperatures of two SCRAM-9 samples under different heat treatments showed that the increase of temperature can promote the diffusion of hydrogen atom and increase the hydrogen diffusion coefficient.For SCRAM-9,the temperature dependence of hydrogen diffusion coefficient conforms with the Arrhenius relationship.Mechanical alloying?MA?and spark plasma sintering?SPS?methods were used to prepare ODS steel with N element.The effects of different N content and N source on hydrogen permeation behavior of ODS steel were studied.Firstly,the hydrogen diffusion coefficients of ODS steel using CrN as N source with different N content were compared.The results showed that the hydrogen diffusion coefficient of ODS steel decreases with the increase of N content,and the hydrogen diffusion coefficient of ODS steel with 1 wt%N content was 1/6 of ODS steel without N element.Then ODS steel with 1 wt%N content was prepared by using different N sources.It was found that ODS steel using TiN as N source had a lower hydrogen diffusion coefficient.The hydrogen permeation of ODS steel with different TiN contents was further studied.The results showed that TiN can significantly decrease the hydrogen diffusion coefficient of ODS steel,and the hydrogen diffusion coefficient of ODS steel decreases with the increase of TiN content.The adsorption of H atom on different crystal orientation of TiN and VN were calculated based on the first principle by using Material Studio software.For both?220?and?200?surface,there are only one termination,while for?111?surface,there are two terminations.The most surface was Ti?V?or the most surface was N.The results showed that the adsorption energy of hydrogen on different surfaces of TiN and VN were all negative.Under same adsorption condition,for the?200?,?111?surface with higher crystal phase content,the adsorption energy of TiN is larger than that on the VN surface,and the adsorption energy of the?220?surface with the lowest crystal phase content is smaller than that on the VN surface.These results indicated that the adsorption process was a spontaneous process,and the adsorption of hydrogen atom by TiN may be stronger than that of VN.Therefore,the TiN particles in the matrix may be more effectively in hindering the diffusion of hydrogen than VN particles.A preliminary exploration of the organic electrolyte solutions for electrochemical hydrogen permeation test was carried out.Glycerol+sodium dihydrogen phosphate+a small amount of phosphoric acid may be used for hydrogen permeation test at high temperatures,but the hydrogen diffusion coefficient was smaller than test in aqueous solution due to their conductivity.[Glycerol+water?66.7%glycerin?]+sodium dihydrogen phosphate+a small amount of phosphoric acid may be used for electrochemical hydrogen permeation test at low temperatures.The hydrogen diffusion coefficient measured was slightly smaller than test in aqueous solution.