Hydrogen Isotope Permeation And Retention Behavior In Fusion Materials And Components

Deuterium(D)and tritium(T)nuclear fusion reaction is the easiest one to be realized on the earth.Tokamak is regarded as one of the most promising methods for the controlled nuclear fusion by magnetic confinement.The ITER project is financed by the European Union,Japan,the United States,China,Russia,Korea and India.China also proposes the China Fusion Engineering Test Reactor(CFETR)project.Owing to the scarcity and radioactivity of T,T permeation and retention behavior is one of the most important issues for the economy and safety concern of nuclear fusion reactors.In order to obtain systematic knowledge about the hydrogen isotopes permeation and retention behavior in fusion materials and components,some hydrogen transport detection techniques such as Thermal Desorption Spectroscopy(TDS),Gas Driven Permeation(GDP),Plasma Driven Permeation(PDP)and Material and Plasma Evaluation System(MAPES)in EAST combined with some material characterization techniques such as Scanning Electron Microscope(SEM),Transmission Electron Microscope(TEM),X-ray Photoelectron Spectroscopy(XPS)and Positron Annihilation Spectroscopy(PAS)are utilized to study the D retention and permeation behavior in fusion structural materials and plasma facing materials.At last,D PDP experiments through plasma facing component(PFC)mock up are performed.The structural materials include Reduced Activation Ferritic/Martensitic(RAFM)steel(i.e CLF-1 steel,CLAM steel and Eurofer steel),vanadium alloys(i.e.pure vanadium and V-4Cr-4Ti alloy),copper alloys(i.e.pure copper,oxygen free copper OFC,Al2O3 dispersion strengthening copper AL15 and CuCrZr alloy).The plasma facing materials include the rolled tungsten and redeposited tungsten on RAFM steel.The PFC mock up is the divertor monoblock mock up.In this work,the first PDP set up is established in China.The D recombination coefficients on homemade RAFM steel and tungsten are obtained by the PDP set up.The PDP set up is also established in EAST.The first D permeation signal is recorded in the wall conditioning process.The PDP experiments indicate that(1)the ion incident energy increases,the D recombination coefficients on RAFM steel increase and the PDP fluxes decrease.It is related to the surface impurities on RAFM steel under different ion incident energies.The surface of the Test Blanket Module(TBM)made of RAFM steel is cleaner,the T permeation flux is lower,which is beneficial for the evaluation of T breeding capability of blankets.(2)The PDP fluxes for the V-4Cr-4Ti alloy are higher than GDP fluxes at the same D2 gas pressure.The PDP fluxes also decrease with the increase of ion incident energy.(3)The PDP fluxes through the CuCrZr alloy are close to those through pure copper as well.(4)D recombination coefficients on tungsten is also related to the surface condition.The activation energy of D recombination coefficients changes with the chemical adsorption energy of surface impurities.(5)Compared with the bare RAFM steel,6 μm thick tungsten deposited on RAFM steel reduces the D permeation flux.However,30 nm thick tungsten deposited on RAFM steel increases the D permeation flux.(6)The first proof-of-principle experiments on D transport through ITER-like PFC mock-ups are conducted.It indicates that the T neutral particles do not need to permeate through 8 mm thick tungsten armor material but through structural materials(i.e.1.5 mm thick CuCrZr alloys or 0.4 mm thick RAFM steel)at the bottom of the tungsten tile gaps and enter into the coolant.In ITER divertor area,the charge exchange neutral particles could reach 1024 m-2s-1.The permeation fluxes through heat sink tube may be large,which may increase tritiated water amount and cause T safety issue.If CFETR divertor adopts the similar design as EAST upper divertor,i.e.adding a tungsten ring between the tungsten tile gaps,which could fix positions of tungsten tiles and reduce the T permeation fluxed through structural materials.The D transport parameters(i.e.permeability and diffusivity)of fusion materials are obtained.The experiments for the structural materials show that(1)the permeability and diffusivity of D in homemade RAFM steel are close to those in other oversea RAFM steels.(2)The permeability of D in V-4Cr-4Ti alloy is close to that in pure vanadium,but two orders of magnitude higher than that of RAFM steel.The diffusivity of D in V-4Cr-4Ti alloy is lower than that in pure vanadium,which is related to the addition of Ti element.The blanket made of V-4Cr-4Ti alloy should have higher requirements for T barrier,T safety and T circulation.(3)The diffusion coefficients of D in copper alloys from lower level to higher level are CuCrZr alloy,AL15 and pure copper.The permeability of D in the three copper alloys is close to each other.(4)The effective diffusivity of D in rolled tungsten is much lower than the lattice diffusivity of D in tungsten.It could be attributed to the high dislocation density in rolled tungsten.High temperature annealing treatment could reduce the dislocation density in rolled tungsten.The D retention behavior in fusion materials is evaluated.The conclusions are that(1)D retention in RAFM steel increases with irradiation damage in top surface(-0.16μm),but irradiation damage in the subsurface(～1.2 μm)has no significant effect on the D retention.The pre-injected He ions in the top surface(-0.03 μm)show strong trapping effect.The pre-injected He ions in the subsurface(-6.1 μm)reduce the D inventory.The D retention in He pre-injected RAFM steel depends on the competition of trapping effect and barrier effect.(2)The D inventory in V-4Cr-4Ti alloy is slightly higher than that in pure vanadium,but two orders of magnitude higher than that in RAFM steel.(3)D inventory in copper alloys from lower level to higher level is pure copper,AL15 and CuCrZr a lloy.The D retention in CuCrZr alloy is mainly related to.the dissolved Zr content in the substrate.The D trapping energy for dissolved Zr in CuCrZr alloy is 0.98 eV.The decrease of dissolved Zr in the substrate in the preparation and the following heat treatment process for CuCrZr alloy could reduce T retention.(4)Compared with the bare RAFM steel,30 nm thick tungsten deposited on RAFM steel has no significant effect on D retention,while 6 μm thick tungsten deposited on RAFM steel reduces the D inventory.(5)The D desorption behavior for the samples after EAST plasma exposure is different from that for the samples after ECR plasma exposure,which is related to the complex environment(i.e.impurities,particle species,particle energy distribution,particle flux distribution)in EAST.More information about particle species,particle fluxes,particle energies and the surface condition of PFMs is favorable to evaluate the T inventory and permeation fluxes in fusion reactors.