Study On Irradiation Effect Of Tritium Decay On Polyvinyl Alcohol Membrane

The polyvinyl alcohol (PVA) was widely used as a kind of deuterium-tritium (DT) fuel gas-barrier material for multilayer plastic microsphere in inertial confinement fusion (ICF) experiments. The samples of PVA films were exposed to a mixture of DT gas at different temperature, pressure and time. The radiation effect of PVA films were studied under the different conditions of P-ray from tritium decay. The change of physical and chemical properties of the irradiated material samples were analyzed by FT-IR、GPC、AFM and tensile mechanics.The tritium-hydrogen isotopic exchange reaction of the irradiated PVA samples mainly occurred at C-H bond and the FT-IR absorption peak of C-D bond did’t appear. For strong hydrogen bonding interaction, the isotopic exchange reaction don’t occurred at O-H bond.The samples of PVA films were exposed to 0.6MPa DT gas for 5 days at elevated temperature from 30℃ to 60 ℃. The FT-IR absorption peak intensity of C-T bond at 1700cm-1 increased linearly with the increase of DT gas temperature, and the amount of C-H bond changed to C-T bond in the irradiated PVA samples increased linearly from 5.4% to 12.2%. The activation energies of tritium-hydrogen isotopic exchange reaction of C-H bond in the irradiated PVA samples were 22.57kJ/mol. The isotopic replacement rate of C-H bond by C-T bond was 0.046%·d-1·℃-1 of the amount of C-H bond in the original PVA films. The amount of alcoholic hydroxyl-OH bond damaged with β radiation in the irradiated PVA samples increased exponentially from 14.14% to 43.25% with the increase of DT gas temperature. The elongation percentage of the irradiated PVA samples decreased linearly from121.0% to 65.4% with the increase of DT gas temperature.The samples of PVA films were exposed to 0.6MPa DT gas at 25℃ for the time range of 10d-30d. The FT-IR absorption peak intensity of C-T bond at 1704cm-1 increased linearly with the increase of radiation time, and the amount of C-H bond changed to C-T bond in the irradiated PVA samples increased linearly from 8.1% to 12.5%. The isotopic replacement rate of C-H bond by C-T bond was 0.219%·d-1 of the amount of C-H bond in the original PVA films. The amount of alcoholic hydroxyl-OH bond damaged with β radiation in the irradiated PVA samples increased linearly from 11.13% to 16.93% with the increase of radiation time. The radiation damage rate of alcoholic hydroxyl-OH bond was 0.302%·d-1 of the amount of alcoholic hydroxyl-OH bond in the original PVA films. The elongation percentage of the irradiated PVA samples decreased linearly from 163.8% to 32.7% with the increase of radiation time.The samples of PVA films were exposed to 0.2MPa-0.9MPa DT gas for 15 days at 25℃. The FT-IR absorption peak intensity of C-T bond at 1704cm-1 increased linearly with the increase of DT gas pressure, and the amount of C-H bond changed to C-T bond in the irradiated PVA samples increased linearly from 1.4% to 5.0%. The isotopic replacement rate of C-H bond by C-T bond was 0.330%·d-1·MPa-1 of the amount of C-H bond in the original PVA films. The amount of alcoholic hydroxyl-OH bond damaged with β radiation in the irradiated PVA samples increased linearly from 4.94% to 18.24% with the increase of DT gas pressure. The elongation percentage of the irradiated PVA samples decreased linearly from 245.6% to 5.3% with the increase of DT gas pressure.The radiation effect of PVA films irradiated by tritium decay was mainly-C-C-main chain bond rupture and degradation. The weight average molecular weight (Mw) of PVA films decreased gradually from 148600 to 21000 with the increase of DT gas pressure. The molecular weight distribution (Mw/Mn) of PVA films increased linearly from 1.35 to 2.05 with the increase of DT gas pressure. The number of low-molecular-weight molecules became more and more with the increase of DT gas pressure.The samples of PVA films were exposed to 0.6MPa DT gas for 10 days at 25℃. The permeabilities of deuterium through the irradiated PVA samples over the temperature range of 20℃～65℃ were studied. The deuterium permeability coefficient increased exponentially from 1.01×10-18 mol·m/m2·s· Pa to 3.6×10-17 mol·m/m2·s· Pa with the increase of temperature. The deuterium permeation activation energy of the irradiated PVA samples was 74.25kJ/mol. The deuterium permeability coefficient and permeation activation energy of the irradiated PVA samples increased rapidly.