Evaluation Of Iron Based Tritium Permeation Barrier Materials And Investigation Of Their Key Performance

Due to the high hydrogen permeability and solubility in the reduced activation ferritic/martensitic(RAFM)steels,which have been regarded as the main candidate structural material of blanket,it is necessary to prepare a tritium permeation barrier with good hydrogen permeation reduction ability on the RAFM steel.To meet the requirements,firstly,the hydrogen permeation and retention behavior of the RAFM steel has been studied to provide hydrogen transport parameters of the substrate for the tritium permeation barrier.Two approaches have been conducted to prepare ceramic tritium permeation barrier on the RAFM steel.One of the approach is to oxidize the RAFM steel directly to obtain a tritium permeation barrier which mainly consisted of chromium oxide.With a view to the real work conditions of the RAFM steels,high temperature oxidation as well as high temperature and pressure water oxidation have been performed to oxidize the RAFM steels,and the hydrogen permeation behavior of the oxidized RAFM steels as well as the microstructure evolution have been studied.The experimental results have shown that the polyporous oxide layer formed on the RAFM steel cannot provide enough hydrogen permeation reduction ability.The other approach is to prepare a Fe-Cr-Al layer on the RAFM steel and then oxidize the Fe-Cr-Al layer to form the tritium permeation barrier(TPB)which mainly consisted of aluminum oxide.Efforts have been done to optimize the oxidation atmosphere,oxidation time and surface roughness to obtain better permeation reduction ability.The influence of irradiation on the oxidized Fe-Cr-Al has been studied and the stability of the material after irradiation has been confirmed.Based on the cold spray method,the connecting process of the Fe-Cr-Al and RAFM steel as well as their oxidation process have been studied.The research results in this study provide data support for the preparation of the TPB for the demonstration reactor(DEMO)and fusion reactor,which are significant important for the realization of the tritium self-sustaining.The main research results are listed below:Firstly,the deuterium permeation behavior of a newly developed RAFM steel,named SIMP steel,has been studied.The hydrogen transport parameters of the SIMP steel in the work temperature regime have been first obtained.The results show that the deuterium diffusion coefficient and permeability of the SIMP steel are similar to other RAFM steels.The retention behavior of the deuterium in the RAFM steel under different deuterium introducing methods has also been studied.These results enrich the database of the home made RAFM steels and provide the reference data of the hydrogen permeation parameters for the substrate of the TPB samples.Then,high temperature oxidation in the air and high temperature and high pressure oxidation in the water have been employed to form oxide layer on the RAFM steel for the purpose of reducing the hydrogen isotope permeability of the RAFM steel.The SIMP steel and CLF-1 steel were oxidized in the air at 800℃ to obtain the oxide layer which mainly consisted of chromium oxide.After oxidation,an oxide layer contained iron oxide and chromium oxide with a thickness up to micrometer was obtained on the SIMP steel.Holes have been observed in the oxide layer.The main chemical composition in the oxide layer of CLF-1 steel is chromium oxide.The gas driven permeation(GDP)experiments show that the reduction of deuterium permeability of oxidized SIMP steel and CLF-1 steel are lower than one order.Then,the CLF-1 steel was oxidized in high temperature and high pressure water for 500 h.The temperature of the water was 325℃ and the pressure was 15.5 MPa.The dissolved oxygen in the pressured water was set as 10 ppb and 200 ppb.The hydrogen isotopes permeation behavior of the oxidized CLF-1 steel has been studied.After oxidation,an oxide layer contained chromium oxide and iron oxide was obtained.The reduction of deuterium permeability of the oxidized CLF-1 steel is lower than one order compared with that of the original CLF-1 steel.The hydrogen permeation reduction ability obtained through above two methods cannot meet the requirement of the future fusion reactor.Based on the results that the hydrogen permeation reduction ability obtained through oxidizing the RAFM steel directly is limited,we attempt to prepare a Fe-Cr-Al layer on the RAFM steel first and then oxidizing them to obtain TPB oxide layer contained aluminum oxide.In order to optimize the hydrogen permeation reduction ability of the oxidized Fe-Cr-Al,an oxidation device with adjustable oxidation atmosphere and real time atmosphere monitor ability was constructed to study the influence of different oxygen content in the oxidation atmosphere.GDP experiments show that the Fe-Cr-Al oxidized in Ar-1700 ppm O2 shows the lowest deuterium permeability,which is 104 times lower than that of the typical RAFM steel at 550℃.The main content in the oxide layer of the Fe-Cr-Al oxidized in low oxygen atmosphere is aluminum oxide.The thickness of the oxide layer is about 50-120 nm.These experiments show that the low oxygen content in the oxidation atmosphere could reduce the iron oxide and chromium oxide content in the oxide layer.Thus,a more condense alumina layer could be formed to provide outstanding tritium permeation reduction ability.Experimental results show that the surface roughness has no influence on the deuterium permeation behavior of the oxidized Fe-Cr-Al steel.The TPB materials working in the blanket of fusion reactor will suffer neutron irradiation.Considering into this condition,the high energy Au ions irradiation experiments have been performed for the oxidized Fe-Cr-Al to simulate the neutron irradiation.Two different irradiation dose have been introduced into the oxide layer.The displacement damage in the oxide layer are almost uniform distributed and the average dpa is about 1.2 and 12.The GDP experiments show that the reduction of deuterium permeability of the irradiated samples is lower than one order compared with that of the original sample.After high temperature treatment,the deuterium permeability of the irradiated samples are similiar to that of the original sample.Combined with the positron annihilation experiments,it can be found that the displacement damage has limited influence on the deuterium permeation reduction ability of the oxidized Fe-Cr-Al.Finally,to realize the engineering application of the oxidized Fe-Cr-Al material,cold spray has been attempt to connect the Fe-Cr-Al and RAFM steel,then thermal oxidation was employed to oxidize the Fe-Cr-Al layer.The thickness of the coating prepared by the cold spray is about 320 μm.After 100 h oxidation during 800℃ in the air,the main content in the oxide layer is alumina.GDP experiments show that the deuterium permeability is 2 order of magnitude lower than that of the original RAFM steel after TPB prepared using cold spray.These experiments provide data base for the engineering application of the thermal oxidation Fe-Cr-Al TPB material.