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2015 Volume 31 Issue S1
2015, 31(S1): 3-13
doi: 10.3866/PKU.WHXB2014Ac01
Abstract:
As the most complex element, plutonium and its compounds have long been intensively studied and a large number of remarkable scientific breakthroughs have been reported frequently in the literature. However, modern-day problems concerning plutonium involve predicting its properties under long-term aging in storage environments. Because of its high chemical activity and strong α radioactive decay, plutonium is vulnerable to chemical and physical aging, which can produce macroscopic effects such as surface corrosion, swelling, and degradation of its mechanical properties. Unfortunately, plutonium is one of the most unusual metals and even the most extensively studied plutonium phase diagram, electronic structure and surface structure have been controversial to date. Therefore, developing a predictive aging model for plutonium is a major goal for many laboratories internationally. Such predictions require multi-scale modeling, which until now has not existed. In this paper, progress in theoretical investigations on plutonium, especially first-principles calculations of its electronic structure and atomic-scale simulation of self-radiation damage, is briefly reviewed. Moreover, the feasibility of various density functional theory (DFT) calculations and atomic-scale simulation methods used in plutonium-based solid-state materials studies is discussed. Finally, future directions in this research field are presented.
As the most complex element, plutonium and its compounds have long been intensively studied and a large number of remarkable scientific breakthroughs have been reported frequently in the literature. However, modern-day problems concerning plutonium involve predicting its properties under long-term aging in storage environments. Because of its high chemical activity and strong α radioactive decay, plutonium is vulnerable to chemical and physical aging, which can produce macroscopic effects such as surface corrosion, swelling, and degradation of its mechanical properties. Unfortunately, plutonium is one of the most unusual metals and even the most extensively studied plutonium phase diagram, electronic structure and surface structure have been controversial to date. Therefore, developing a predictive aging model for plutonium is a major goal for many laboratories internationally. Such predictions require multi-scale modeling, which until now has not existed. In this paper, progress in theoretical investigations on plutonium, especially first-principles calculations of its electronic structure and atomic-scale simulation of self-radiation damage, is briefly reviewed. Moreover, the feasibility of various density functional theory (DFT) calculations and atomic-scale simulation methods used in plutonium-based solid-state materials studies is discussed. Finally, future directions in this research field are presented.
2015, 31(S1): 14-18
doi: 10.3866/PKU.WHXB2014Ac06
Abstract:
Separation and purification methods for trace thorium and other impurity elements in uranium are important. Accurate and precise measurements can be made using isotope dilution mass spectrometry. In this study, we spiked samples with 230Th using alkaline anion exchange and tri-n-butyl phosphate (TBP) extraction chromatography stack columns for separating trace thorium and other impurity elements in uranium from an 8 mol·L-1 nitric acid medium. In this separation method, thorium was adsorbed on the alkaline anion exchange resin, uranium was adsorbed on the TBP chromatography powder, and other impurity elements were not adsorbed on the alkaline anion exchange resin or the TBP chromatography powder. The purified thorium samples were analyzed using thermal ionization mass spectrometry. The results showed that the thorium content in uranium was (59.3±0.1) μg·g-1, the expanded factor (k) was 2, and the confidence was 95%.
Separation and purification methods for trace thorium and other impurity elements in uranium are important. Accurate and precise measurements can be made using isotope dilution mass spectrometry. In this study, we spiked samples with 230Th using alkaline anion exchange and tri-n-butyl phosphate (TBP) extraction chromatography stack columns for separating trace thorium and other impurity elements in uranium from an 8 mol·L-1 nitric acid medium. In this separation method, thorium was adsorbed on the alkaline anion exchange resin, uranium was adsorbed on the TBP chromatography powder, and other impurity elements were not adsorbed on the alkaline anion exchange resin or the TBP chromatography powder. The purified thorium samples were analyzed using thermal ionization mass spectrometry. The results showed that the thorium content in uranium was (59.3±0.1) μg·g-1, the expanded factor (k) was 2, and the confidence was 95%.
2015, 31(S1): 19-24
doi: 10.3866/PKU.WHXB2014Ac19
Abstract:
A dry conversion process to produce UO2 powder is reported. Uranium fluoride (UF6) is directly hydrolyzed with water vapor from a concentric nozzle to form uranyl fluoride (UO2F2), which is transferred to a rotary kiln by a screw and reduced to ceramic-grade uranium dioxide (UO2) powder with backward mixing gases of vapor and hydrogen. Several of the main reactions and thermodynamics calculations for conversion of gaseous UF6 to UO2 powder are reported, including reactions for UO2F2+H2O/H2→UO2/UO3 and UO2+HF→UF4. The influence of the temperature of the first zone and the gas atmosphere of H2O-H2-HF on the fluorization of UO2 by HF in term of thermodynamics are also discussed. Moreover, the influences of the dry conversion process parameters on the UO2 physical properties are analyzed by qualification test results.
A dry conversion process to produce UO2 powder is reported. Uranium fluoride (UF6) is directly hydrolyzed with water vapor from a concentric nozzle to form uranyl fluoride (UO2F2), which is transferred to a rotary kiln by a screw and reduced to ceramic-grade uranium dioxide (UO2) powder with backward mixing gases of vapor and hydrogen. Several of the main reactions and thermodynamics calculations for conversion of gaseous UF6 to UO2 powder are reported, including reactions for UO2F2+H2O/H2→UO2/UO3 and UO2+HF→UF4. The influence of the temperature of the first zone and the gas atmosphere of H2O-H2-HF on the fluorization of UO2 by HF in term of thermodynamics are also discussed. Moreover, the influences of the dry conversion process parameters on the UO2 physical properties are analyzed by qualification test results.
2015, 31(S1): 25-31
doi: 10.3866/PKU.WHXB2014Ac08
Abstract:
We have preliminarily developed the experimental study of UF4 and its thermal chemical reaction characteristics in environmental atmospheres such as air, O2, and hydrated O2. Various analytical techniques such as micro-laser Raman spectroscopy (MLRS), X-ray photoelectron spectroscopy (XPS), and metallography were used. Based on the physical and chemical properties of UF4, we obtained the Raman and XPS spectra of different uranium compounds after heating at specific temperatures for specific times. The experimental results indicate that UF4 is stable up to 200 ℃ in various atmospheres. Raman spectra were almost unchanged. However, above 250 ℃, the surface color of UF4 changed significantly. Raman spectrum and XPS analyses showed that a variety of uranium compounds such as UO2, UO2F2, and U3O8 were formed. In this work, we calculated the apparent activation energies of the reactions of UF4 with active gases in the environment, and studied the relationship between the reaction rate and temperature in detail.
We have preliminarily developed the experimental study of UF4 and its thermal chemical reaction characteristics in environmental atmospheres such as air, O2, and hydrated O2. Various analytical techniques such as micro-laser Raman spectroscopy (MLRS), X-ray photoelectron spectroscopy (XPS), and metallography were used. Based on the physical and chemical properties of UF4, we obtained the Raman and XPS spectra of different uranium compounds after heating at specific temperatures for specific times. The experimental results indicate that UF4 is stable up to 200 ℃ in various atmospheres. Raman spectra were almost unchanged. However, above 250 ℃, the surface color of UF4 changed significantly. Raman spectrum and XPS analyses showed that a variety of uranium compounds such as UO2, UO2F2, and U3O8 were formed. In this work, we calculated the apparent activation energies of the reactions of UF4 with active gases in the environment, and studied the relationship between the reaction rate and temperature in detail.
2015, 31(S1): 32-38
doi: 10.3866/PKU.WHXB2014Ac10
Abstract:
The selective extraction of UO22+ from aqueous solution in the presence of other metal ions by octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and tri-n-butyl phosphate (TBP) in ionic liquids (ILs), namely 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides (CnmimNTf2, n=2, 4, 6, 8), were studied. The influences of the nitric acid concentration and the IL alkyl chain length on the distribution ratio and selectivity were examined. Compared with TBP in C4mimNTf2, CMPO in the ILs gave higher distribution ratios and better selectivities. Zr4+, ReO4-, and Cs+ were the main competing ions in the separation of UO22+ from simulated liquid waste (SLM) by the CnmimNTf2 systems. ReO4- and Cs+ were extracted by the ILs themselves. Zr4+ was extracted by CMPO or TBP in the ILs but not by the ILs themselves. This work gives further information on the use of ILs, and provides a basis for matching extractants with ILs in the processing of spent nuclear fuel.
The selective extraction of UO22+ from aqueous solution in the presence of other metal ions by octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and tri-n-butyl phosphate (TBP) in ionic liquids (ILs), namely 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides (CnmimNTf2, n=2, 4, 6, 8), were studied. The influences of the nitric acid concentration and the IL alkyl chain length on the distribution ratio and selectivity were examined. Compared with TBP in C4mimNTf2, CMPO in the ILs gave higher distribution ratios and better selectivities. Zr4+, ReO4-, and Cs+ were the main competing ions in the separation of UO22+ from simulated liquid waste (SLM) by the CnmimNTf2 systems. ReO4- and Cs+ were extracted by the ILs themselves. Zr4+ was extracted by CMPO or TBP in the ILs but not by the ILs themselves. This work gives further information on the use of ILs, and provides a basis for matching extractants with ILs in the processing of spent nuclear fuel.
2015, 31(S1): 39-44
doi: 10.3866/PKU.WHXB2014Ac14
Abstract:
To investigate the difference of the hydride growth kinetics of U, U-2.5%Nb, and U-5.7%Nb (mass fraction) based on strain energy theory, the deformation, stress, and strain energy during hydride growth were investigated by the finite element model (FEM) according to the mechanical properties of the three U materials. The results showed that the strain energy because of hydride expansile growth in the matrix is considerably different for the three U materials. When hydride grows, the order of the strain energy value is U-5.7%Nb > U > U-2.5%Nb. This indicates that based on reaction activation energy theory the U-2.5%Nb alloy is the most susceptible to hydrogen corrosion, followed by U, while U-5.7%Nb is the most resistant to hydrogen corrosion. The calculated results of the strain energy agree with the hydride growth kinetics experimental results, which also show that the hydride growth model is correct. This study shows that the large strain energy because volume change during hydride growth plays an important role in the growth kinetics.
To investigate the difference of the hydride growth kinetics of U, U-2.5%Nb, and U-5.7%Nb (mass fraction) based on strain energy theory, the deformation, stress, and strain energy during hydride growth were investigated by the finite element model (FEM) according to the mechanical properties of the three U materials. The results showed that the strain energy because of hydride expansile growth in the matrix is considerably different for the three U materials. When hydride grows, the order of the strain energy value is U-5.7%Nb > U > U-2.5%Nb. This indicates that based on reaction activation energy theory the U-2.5%Nb alloy is the most susceptible to hydrogen corrosion, followed by U, while U-5.7%Nb is the most resistant to hydrogen corrosion. The calculated results of the strain energy agree with the hydride growth kinetics experimental results, which also show that the hydride growth model is correct. This study shows that the large strain energy because volume change during hydride growth plays an important role in the growth kinetics.
2015, 31(S1): 45-48
doi: 10.3866/PKU.WHXB2014Ac05
Abstract:
PHREEQC software was used to study the chemical form of uranium based on the chemical composition of groundwater from a low-level radioactive waste repository located in southwest China. The effects of pH, temperature, and pE (the equilibrium state of electronic activity) on the distribution in uranium chemical form were studied. The results show that uranium presents in the VI chemical valence and [UO2(CO3)2]2-, [UO2(CO3)3]4-, and UO2CO3 forms when pH=7.6, T=12.2 ℃, and pE=4 in groundwater. Temperature and pH strongly impact the distribution of the uranium chemical form. However, pE has little effect on the chemical form distribution. Therefore, pH and groundwater temperature should be taken key considerations during the selection of waste landfill sites.
PHREEQC software was used to study the chemical form of uranium based on the chemical composition of groundwater from a low-level radioactive waste repository located in southwest China. The effects of pH, temperature, and pE (the equilibrium state of electronic activity) on the distribution in uranium chemical form were studied. The results show that uranium presents in the VI chemical valence and [UO2(CO3)2]2-, [UO2(CO3)3]4-, and UO2CO3 forms when pH=7.6, T=12.2 ℃, and pE=4 in groundwater. Temperature and pH strongly impact the distribution of the uranium chemical form. However, pE has little effect on the chemical form distribution. Therefore, pH and groundwater temperature should be taken key considerations during the selection of waste landfill sites.
2015, 31(S1): 49-53
doi: 10.3866/PKU.WHXB2014Ac11
Abstract:
We describe the preparation of single-valence solutions of Pu and the identification of Pu ions with different valences via their ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopic characteristics. The optimal experimental conditions were established, and then three types of Pu stock solution, i.e., Pu(III), Pu(IV), and Pu(VI), were prepared by redox reactions in HCl solution. We investigated their UV- Vis absorption spectroscopic properties. The characteristic absorption peaks were identified for Pu(III) (560, 600, 665, 900 nm), Pu(IV) (470, 550, 660, 795 nm), and Pu(VI) (835, 950, 990 nm). We used these results to develop a method for identifying Pu ions via their characteristic absorption peaks. The conclusions are in accordance with those reported in previous work, and provide a new technique for subsequent research.
We describe the preparation of single-valence solutions of Pu and the identification of Pu ions with different valences via their ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopic characteristics. The optimal experimental conditions were established, and then three types of Pu stock solution, i.e., Pu(III), Pu(IV), and Pu(VI), were prepared by redox reactions in HCl solution. We investigated their UV- Vis absorption spectroscopic properties. The characteristic absorption peaks were identified for Pu(III) (560, 600, 665, 900 nm), Pu(IV) (470, 550, 660, 795 nm), and Pu(VI) (835, 950, 990 nm). We used these results to develop a method for identifying Pu ions via their characteristic absorption peaks. The conclusions are in accordance with those reported in previous work, and provide a new technique for subsequent research.
2015, 31(S1): 54-58
doi: 10.3866/PKU.WHXB2014Ac15
Abstract:
In fusion and fission energy devices, the first wall/cladding structure materials are in a harsh environment. The effect of hydrogen and helium produced by transmutation on the structural materials is one of the critical problems for future nuclear reactors. Ti3SiC2 is a high performance ceramic material that combines the advantages of ceramics and metals, and it has excellent resistance to irradiation damage. In this work, the helium diffusion constants and concentration profiles in Ti3SiC2 from 400 to 1100 ℃ were obtained using the resonant 3He (d, p) 4He nuclear reaction, and the helium diffusion behavior is also discussed. The concentration profiles were found to change because of the interaction between helium evolution and stress in the material.
In fusion and fission energy devices, the first wall/cladding structure materials are in a harsh environment. The effect of hydrogen and helium produced by transmutation on the structural materials is one of the critical problems for future nuclear reactors. Ti3SiC2 is a high performance ceramic material that combines the advantages of ceramics and metals, and it has excellent resistance to irradiation damage. In this work, the helium diffusion constants and concentration profiles in Ti3SiC2 from 400 to 1100 ℃ were obtained using the resonant 3He (d, p) 4He nuclear reaction, and the helium diffusion behavior is also discussed. The concentration profiles were found to change because of the interaction between helium evolution and stress in the material.
2015, 31(S1): 59-63
doi: 10.3866/PKU.WHXB2014Ac07
Abstract:
The α radioactive decay of Pu by self-irradiation in the δ-Pu alloy markedly changes its microstructure and macro mechanical properties. Helium bubbles, the main product of self-irradiation, can affect the plastic behavior of δ-Pu by impeding the movement of dislocations. In this paper, we first derive a relationship between the volume ratio of helium bubbles and aged time. We then introduce the effect of helium bubbles on the critical resolved shear stress for dislocation motion and the growth law for helium bubbles into a constitutive model to obtain the dislocation-based static constitutive functions of δ-Pu. Model parameters are then fitted using experiment data. Finally, the stress-strain curves of δ-Pu for different aged times are presented.
The α radioactive decay of Pu by self-irradiation in the δ-Pu alloy markedly changes its microstructure and macro mechanical properties. Helium bubbles, the main product of self-irradiation, can affect the plastic behavior of δ-Pu by impeding the movement of dislocations. In this paper, we first derive a relationship between the volume ratio of helium bubbles and aged time. We then introduce the effect of helium bubbles on the critical resolved shear stress for dislocation motion and the growth law for helium bubbles into a constitutive model to obtain the dislocation-based static constitutive functions of δ-Pu. Model parameters are then fitted using experiment data. Finally, the stress-strain curves of δ-Pu for different aged times are presented.
2015, 31(S1): 64-68
doi: 10.3866/PKU.WHXB2014Ac17
Abstract:
The agglomeration of helium atoms created by nuclear fission in plutonium is an important factor in plutonium aging. Using molecular dynamic simulation we found that atomic collision cascades had a significant effect on the stability of helium bubbles, which is a possible reason why rate-equation theory cannot well describe helium bubble growth in aged plutonium. We improved Schaldach-Wolfer theory by considering atomic collision cascade effects, and the theoretical results agreed well with the experimental data and predicted the behavior of helium bubbles in plutonium at room temperature in 100 years.
The agglomeration of helium atoms created by nuclear fission in plutonium is an important factor in plutonium aging. Using molecular dynamic simulation we found that atomic collision cascades had a significant effect on the stability of helium bubbles, which is a possible reason why rate-equation theory cannot well describe helium bubble growth in aged plutonium. We improved Schaldach-Wolfer theory by considering atomic collision cascade effects, and the theoretical results agreed well with the experimental data and predicted the behavior of helium bubbles in plutonium at room temperature in 100 years.
2015, 31(S1): 69-74
doi: 10.3866/PKU.WHXB2014Ac09
Abstract:
Based on the redistribution model of solutes for multi-zone refining, zone lengths were optimized to minimize the content of solute in the middle of the sample using a genetic algorithm from biological evolutionary theory. The redistribution of solute in the sample during multi-zone refining was computed with the optimized zone length and a constant zone length. The calculation results showed that the efficiency of zone refining with the optimized zone length was significantly better than that with the constant zone length. A low impurity concentration in the 80% part of the middle sample can be achieved after 15 passes of zone refining using the optimized zone lengths.
Based on the redistribution model of solutes for multi-zone refining, zone lengths were optimized to minimize the content of solute in the middle of the sample using a genetic algorithm from biological evolutionary theory. The redistribution of solute in the sample during multi-zone refining was computed with the optimized zone length and a constant zone length. The calculation results showed that the efficiency of zone refining with the optimized zone length was significantly better than that with the constant zone length. A low impurity concentration in the 80% part of the middle sample can be achieved after 15 passes of zone refining using the optimized zone lengths.
2015, 31(S1): 75-80
doi: 10.3866/PKU.WHXB2014Ac03
Abstract:
First-principle calculations of 5fn (n=0-7) electronic configurations are performed with several density functional theory (DFT) methods to describe the localized/delocalized states and obtain the precise population of the 5f manifold in delta-plutonium (δ-Pu). The results show that spin polarization clearly reduces the cohesive energies of each electronic configuration, and enhances the cohesion properties. For 5f0, 5f1, 5f3, 5f4, and 5f6 electronic configurations, the cohesive energies obtained by the spin- polarized local density approximation (SP-LDA)+U method are markedly smaller than that by the SP-LDA method when the lattice constant of δ-Pu exceeds 0.475 nm. The cohesive energies calculated with the spin-polarized generalized gradient approximation (SP-GGA)+U method are smaller than that by SP-GGAmethod, except for 5f4 and 5f6 electronic configurations, and the former trend to coincide with SP-LDA results when the lattice constants are larger than 0.570 nm. For the SP-LDA(GGA)+Umethod, the cohesive energies of 5f0, 5f1, 5f3, 5f4, and 5f6 (5f0, 5f1, 5f2, 5f3, 5f5, and 5f7) electronic configurations are all equal, while the cohesive energies of 5f2, 5f5 (5f4) electronic configurations are the same as that of the 5f7 (5f6) electronic configuration. The cohesive energies of 5fn electronic configurations calculated using the other methods are equal. 5f projected densities of states show that spin polarization results in the exchange split behavior of 5f orbitals. Several 5f states are removed from the Fermi level, which lowers the contribution of 5f states to chemical bonding, and enhances the lattice constant, indicating that strong spin polarization induces partial localization of 5f orbitals. The optimized lattice constants obtained by the SP-LDA method are in good agreement with the experimental values, but the SP-GGA+U method sharply overestimates the lattice constant (by up to about 20%).
First-principle calculations of 5fn (n=0-7) electronic configurations are performed with several density functional theory (DFT) methods to describe the localized/delocalized states and obtain the precise population of the 5f manifold in delta-plutonium (δ-Pu). The results show that spin polarization clearly reduces the cohesive energies of each electronic configuration, and enhances the cohesion properties. For 5f0, 5f1, 5f3, 5f4, and 5f6 electronic configurations, the cohesive energies obtained by the spin- polarized local density approximation (SP-LDA)+U method are markedly smaller than that by the SP-LDA method when the lattice constant of δ-Pu exceeds 0.475 nm. The cohesive energies calculated with the spin-polarized generalized gradient approximation (SP-GGA)+U method are smaller than that by SP-GGAmethod, except for 5f4 and 5f6 electronic configurations, and the former trend to coincide with SP-LDA results when the lattice constants are larger than 0.570 nm. For the SP-LDA(GGA)+Umethod, the cohesive energies of 5f0, 5f1, 5f3, 5f4, and 5f6 (5f0, 5f1, 5f2, 5f3, 5f5, and 5f7) electronic configurations are all equal, while the cohesive energies of 5f2, 5f5 (5f4) electronic configurations are the same as that of the 5f7 (5f6) electronic configuration. The cohesive energies of 5fn electronic configurations calculated using the other methods are equal. 5f projected densities of states show that spin polarization results in the exchange split behavior of 5f orbitals. Several 5f states are removed from the Fermi level, which lowers the contribution of 5f states to chemical bonding, and enhances the lattice constant, indicating that strong spin polarization induces partial localization of 5f orbitals. The optimized lattice constants obtained by the SP-LDA method are in good agreement with the experimental values, but the SP-GGA+U method sharply overestimates the lattice constant (by up to about 20%).
2015, 31(S1): 81-89
doi: 10.3866/PKU.WHXB2014Ac16
Abstract:
Based on the non-local van der Waals density functional (vdW-DF)+U scheme, we have performed a first-principles molecular dynamics (FPMD) study of the interaction dynamics for H2 impingement against the Pu oxide (PuO2) and Pu nitride (PuN) passivation layers on Pu metal surface. Results show that, except for weak physisorption, both the PuO2 and PuN surfaces are so difficult to access that almost all of the H2 molecules will bounce back to the vacuum when their initial kinetic energies are not sufficient. Although dissociative adsorption of H2 on PuO2 surfaces is found to be very exothermic, the collision-induced dissociation barriers of H2 are calculated to be very high. Unfortunately, PuO2 can be reduced to α-Pu2O3 under oxygen-lean conditions. Molecular H2 can easily penetrate and diffuse in α-Pu2O3, and, as a result, α-Pu2O3 can promote the hydrogenation of Pu metal. Unlike PuO2, PuN is found to be a stable and uniform passivation layer against hydrogen-corrosion of Pu, and the interacting system of PuN and H is shown to be thermodynamically unstable. Overall, the current study reveals the different hydrogen-corrosion resistances of PuO2 and PuN passivation layers, which have implications for the interpretation of experimental observations and will be helpful to understand the surface corrosion and passivation of Pu metal.
Based on the non-local van der Waals density functional (vdW-DF)+U scheme, we have performed a first-principles molecular dynamics (FPMD) study of the interaction dynamics for H2 impingement against the Pu oxide (PuO2) and Pu nitride (PuN) passivation layers on Pu metal surface. Results show that, except for weak physisorption, both the PuO2 and PuN surfaces are so difficult to access that almost all of the H2 molecules will bounce back to the vacuum when their initial kinetic energies are not sufficient. Although dissociative adsorption of H2 on PuO2 surfaces is found to be very exothermic, the collision-induced dissociation barriers of H2 are calculated to be very high. Unfortunately, PuO2 can be reduced to α-Pu2O3 under oxygen-lean conditions. Molecular H2 can easily penetrate and diffuse in α-Pu2O3, and, as a result, α-Pu2O3 can promote the hydrogenation of Pu metal. Unlike PuO2, PuN is found to be a stable and uniform passivation layer against hydrogen-corrosion of Pu, and the interacting system of PuN and H is shown to be thermodynamically unstable. Overall, the current study reveals the different hydrogen-corrosion resistances of PuO2 and PuN passivation layers, which have implications for the interpretation of experimental observations and will be helpful to understand the surface corrosion and passivation of Pu metal.
2015, 31(S1): 90-94
doi: 10.3866/PKU.WHXB2014Ac02
Abstract:
Modification of impregnated Co/SiO2 (i-Co/SiO2) and eggshell Co/SiO2 (e-Co/SiO2) through addition of thorium (Th) was obtained by impregnation and spray coating processes, respectively. The effects of thorium on the structure, reduction behavior, and catalytic performance were characterized by X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and CO+H2 reaction. We found that the addition of Th in both impregnation and eggshell catalysts could improve selectivity towards heavy hydrocarbons (C5+) and suppress the formation of methane and light hydrocarbons. In impregnated Co/SiO2 catalysts, the presence of Th could promote dispersion of the active phase to enhance catalytic activity. However, when Th is added to eggshell Co/SiO2 catalysts, it may cover part of the active phase, leading to activity decline.
Modification of impregnated Co/SiO2 (i-Co/SiO2) and eggshell Co/SiO2 (e-Co/SiO2) through addition of thorium (Th) was obtained by impregnation and spray coating processes, respectively. The effects of thorium on the structure, reduction behavior, and catalytic performance were characterized by X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and CO+H2 reaction. We found that the addition of Th in both impregnation and eggshell catalysts could improve selectivity towards heavy hydrocarbons (C5+) and suppress the formation of methane and light hydrocarbons. In impregnated Co/SiO2 catalysts, the presence of Th could promote dispersion of the active phase to enhance catalytic activity. However, when Th is added to eggshell Co/SiO2 catalysts, it may cover part of the active phase, leading to activity decline.
2015, 31(S1): 95-100
doi: 10.3866/PKU.WHXB2014Ac13
Abstract:
Carbon aerogels were prepared, using a freeze-drying method, from graphene oxide (GO) and carbon nanotube (CNT) hybrid hydrogels. The resulting aerogels were characterized using scanning electron microscopy and Fourier-transformed infrared spectroscopy. The adsorption of U(VI) on the GO-CNT aerogels was studied as a function of solid dosage, pH value, initial concentration, and contact time. The results showed that GO-CNT aerogels have high uranium(VI) removal capacities, and are promising sorbents.
Carbon aerogels were prepared, using a freeze-drying method, from graphene oxide (GO) and carbon nanotube (CNT) hybrid hydrogels. The resulting aerogels were characterized using scanning electron microscopy and Fourier-transformed infrared spectroscopy. The adsorption of U(VI) on the GO-CNT aerogels was studied as a function of solid dosage, pH value, initial concentration, and contact time. The results showed that GO-CNT aerogels have high uranium(VI) removal capacities, and are promising sorbents.
2015, 31(S1): 101-105
doi: 10.3866/PKU.WHXB2014Ac18
Abstract:
Surface corrosion of uranium metal during storage for 10 years in an inert gas atmosphere was examined. The factors causing uranium metal surface oxidation, spontaneous combustion, and etch pit formation were investigated using X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the main factors are the iron concentration in the uranium, the long-term and sealed storage conditions, and chemical behaviors of intermediates in the storage environment. UO2 and U3O8 cause etch pits, and the hydrogenation reaction product UH3 combusts spontaneously on exposure to air.
Surface corrosion of uranium metal during storage for 10 years in an inert gas atmosphere was examined. The factors causing uranium metal surface oxidation, spontaneous combustion, and etch pit formation were investigated using X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the main factors are the iron concentration in the uranium, the long-term and sealed storage conditions, and chemical behaviors of intermediates in the storage environment. UO2 and U3O8 cause etch pits, and the hydrogenation reaction product UH3 combusts spontaneously on exposure to air.
2015, 31(S1): 106-110
doi: 10.3866/PKU.WHXB2014Ac12
Abstract:
The Zr-Co alloy is a promising tritium (T)-storage material and has been extensively studied. The helium decayed by T will gather to form bubbles, which are very harmful to the material. The temperature and helium content strongly affect the behavior of helium in the material. In this study, 4He was absorbed in Zr-Co films by magnetron sputtering deposition to simulate the behavior of the 3He decayed by T in T-storage materials. Different He ratio samples were fabricated by radio frequency (RF) magnetron sputtering deposition. The film composition and He ratio in Zr-Co were determined by Rutherford back scattering (RBS) and elastic recoil detection (ERD), respectively. Thermal desorption spectroscopy experiments and X-ray diffraction (XRD) analysis were used to investigate the states of the He in the samples and the microstructure of the samples, respectively.
The Zr-Co alloy is a promising tritium (T)-storage material and has been extensively studied. The helium decayed by T will gather to form bubbles, which are very harmful to the material. The temperature and helium content strongly affect the behavior of helium in the material. In this study, 4He was absorbed in Zr-Co films by magnetron sputtering deposition to simulate the behavior of the 3He decayed by T in T-storage materials. Different He ratio samples were fabricated by radio frequency (RF) magnetron sputtering deposition. The film composition and He ratio in Zr-Co were determined by Rutherford back scattering (RBS) and elastic recoil detection (ERD), respectively. Thermal desorption spectroscopy experiments and X-ray diffraction (XRD) analysis were used to investigate the states of the He in the samples and the microstructure of the samples, respectively.
