Penetration And Surface Adsorption Of Deuterium And Tritium In CLAM Steel

In China Fusion Engineering Test Reactor(CFETR),Reduced Activation Ferritic/Martensitic(RAFM)steel is the preferred structural material for test blanket module in fusion reactor.The tritium growth cladding of the fusion reactor will work in the range from 623K to 923K.In this temperature range,the penetration of tritium in this steel is very serious.And RAFM steel is bce structure,theoretical penetration is more serious than austenitic stainless steel which is fee structure.This will inevitably lead to serious radioactive pollution and tritium waste.The study of the diffusion transport character of deuterium and tritium in the steel is of great significance for fuel recycling,tritium diffusion control,recovery and safety to CFETR item.In order to study the diffusion and permeability of deuterium and tritium in RAFM steel,build the database of interaction between hydrogen isotope and RAFM steel.With deuterium and tritium as the experimental object,the diffusion and migration of deuterium and tritium in the China Low Activation Martensitic(CLAM)steel and the retention of tritium on CLAM steel surface were studied in this work.1)By gas-driven permeation experiment between 573K and 873K,deuterium transport parameters are measured by helium mass spectrometer leak detector.The permeability is:?D(mol/m·s·Pa0.5)= 3.64×10-8exp(-39718/RT),the diffusion coefficient is DD(m2/s)?1.38×10-7exp(-17271/RT),the solubility constant is SD(mol/m3·Pa0.5)= 2.64×10-1exp(-22447/RT).2)Between 573K and 823K,the permeability of tritium is ?T(mol/m·s·Pa0.5)= 2.5×10-8exp(-38493/RT).According to the isotopes effect rule,the diffusion coefficient and solubility constant of tritium is deduced respectively:DT(m2/s)= 2.01×10-7exp(-18496/RT)andST(mol/m3 Pa0.5)= 1.24×10-1exp(-19997/RT).3)CLAM steel is very easy to rust.Once it is produced on the surface,even if it is a thin oxide layer,it will seriously affect the accuracy of measurement data.Therefore,the surface oxidation should be prevented very carefully in the experiment.4)The mixed permeation of hydrogen isotopes is a positive value.For isotopic effect,hydrogen permeability is the largest and tritium permeability is the smallest.For hydrogen and deuterium mixed permeation,the separation coefficient of permeation ?HD =2.65.For deuterium and tritium mixed permeation,the separation coefficient of permeation?DT?1.66.5)A strange behavior appears in experiments with deuterium:after forced air cooling to the steel,the permeation flux through it quickly rise first and then anomaly lower for hours.The mechanism arousing the phenomenon and effects on use in engineering needs further investigation.6)At normal atmospheric temperature,In the atmosphere of 1220Pa the deuterium and tritium mix gas(tritium abundance of 36.5%),CLAM steel was adsorbed for about 12 days.The amount of surface desorption per unit area(cm2)per unit area(total surface adsorption amount per unit area)is 8.59 × 114 Bq/cm2 which was measured by the experiment of gas carrier desorption.The amount of surface desorption per unit area(cm2)is 1.32 x 105Bq/cm2 which was measured by the experiment of soaking and desorption in pure water.By comparing the experimental results of 316L steel and 1Crl 8Ni9Ti steel,it can be seen that the adsorption capacity of CLAM steel is more than that of 316L steel and 1Crl8Ni9Ti steel.Tritium is more likely to form contamination on the surface of CLAM steel and permeate into the material.