The use of molten salts as coolants, fuels, and tritium breeding blankets in the next generation ... more The use of molten salts as coolants, fuels, and tritium breeding blankets in the next generation of fission and fusion nuclear reactors benefits from furthering the characterization of the molecular structure of molten halide salts, paving the way to predictive capability of chemical and thermo-physical properties of molten salts. Due to its neutronic, chemical, and thermo-chemical properties, 2LiF−BeF2 is a candidate molten salt for several fusion and fission reactor designs. We perform neutron and X-ray total scattering measurements to determine the atomic structure of 2LiF−BeF2. We also perform ab-initio and neural network molecular dynamics simulations to predict the structure obtained by neutron and X-ray diffraction experiments. The use of machine learning provides improvements to the efficiency in predicting the structure at a longer length scales than is achievable with ab-initio simulations at significantly lower computational expense while retaining near ab-initio accuracy...
• Hastelloy N and 242, shows corrosion resistance to molten salt at nominal operating temperature... more • Hastelloy N and 242, shows corrosion resistance to molten salt at nominal operating temperatures. • Both diffusion welds and sheet material in Hastelloy N were corrosion tested in at 650, 700, and 850 • C for 200, 500, and 1000 h. • Thermal gradients and galvanic couples in the molten salts enhance corrosion rates. • Corrosion rates found were typically <10 mils per year.
The resurgence of the Molten-Salt Nuclear Reactors (MSR) creates interesting problems in molten-s... more The resurgence of the Molten-Salt Nuclear Reactors (MSR) creates interesting problems in molten-salt chemistry. As MSRs operate, the composition and physical properties of salts change because of fission and corrosion. Since Cr is the principal corrosion product and NaCl is a common constituent, we studied the atomic structure of molten NaCl-CrCl3. We found networks of CrCl3− 6 octahedra and an intermediate-range order with nonmonotonic temperature behavior in a remarkable agreement between measurements and ab initio simulations. Even though the corrosion results in minute quantities of dissolved Cr, the speciation of Cr could lead to changes in molten-salt properties in nuclear and solar salts. In particular, we found a much lower than expected melting temperature and a broad metastable liquid-solid coexistence phase. The availability of Cr isotopes with very different neutron-scattering properties makes Cr an ideal model multi-valent ion for experimental validation of new atomisti...
Recent developments in high-magnetic-field fusion systems have created large incentives to develo... more Recent developments in high-magnetic-field fusion systems have created large incentives to develop flibe (Li 2 BeF 4) salt fusion blankets that have four functions: (1) convert the high energy of fusion neutrons into heat for the power system, (2) convert lithium into tritium-the fusion fuel, (3) shield the magnets against radiation, and (4) cool the first wall that separates the plasma from the salt blanket. Flibe is the same coolant proposed for fluoride-salt-cooled high-temperature reactors that use clean flibe coolant and graphite-matrix coated-particle fuel. Flibe is also the coolant proposed for some molten salt reactors (MSRs) where the fuel is dissolved in the coolant. The multiple applications for flibe as a coolant create large incentives for cooperative fusion-fission programs for development of the underlying science, design tools, technology (pumps, instrumentation, salt purification, materials, tritium removal, etc.), and supply chains. Other high-temperature molten salts are being developed for alternative MSR systems and for advanced Gen-III concentrated solar power (CSP) systems. The overlapping characteristics of flibe salt with these other salt systems create significant incentives for cooperative fusion-fission-solar programs in multiple areas. We describe the fission and fusion flibe-cooled systems, what has created this synergism, what is different and the same between fission and fusion in terms of using flibe, and the common challenges. We review (1) the characteristics of flibe salts, (2) the status of the technology, (3) the options for tritium capture and control in the salt, heat exchangers, and secondary heat transfer loops, and (4) the coupling to power cycles with heat storage. The technology overlap between flibe systems and other high-temperature MSR and CSP salt systems is described. This defines where there are opportunities for cooperative programs across fission, fusion, and CSP salt programs.
The effects of ionizing radiation on materials often reduce to “bad news”. Radiation damage usual... more The effects of ionizing radiation on materials often reduce to “bad news”. Radiation damage usually leads to detrimental effects such as embrittlement, accelerated creep, phase instability, and radiation-altered corrosion. Here we report that proton irradiation decelerates intergranular corrosion of Ni-Cr alloys in molten fluoride salt at 650 °C. We demonstrate this by showing that the depth of intergranular voids resulting from Cr leaching into the salt is reduced by proton irradiation alone. Interstitial defects generated from irradiation enhance diffusion, more rapidly replenishing corrosion-injected vacancies with alloy constituents, thus playing the crucial role in decelerating corrosion. Our results show that irradiation can have a positive impact on materials performance, challenging our view that radiation damage usually results in negative effects.
Hastelloy N Ò , a nickel-based alloy, and 316 stainless steel are among the candidate structural ... more Hastelloy N Ò , a nickel-based alloy, and 316 stainless steel are among the candidate structural materials being considered for the construction of the molten salt reactor (MSR). Most of the proposed MSR concepts use molten fluoride salts as coolant which can be quite corrosive to structural alloys. The results of studies on the corrosion behavior of the two alloys in molten Li 2 BeF 4 (FLiBe) salt at 700°C are discussed. This salt is being considered as the primary coolant for MSR designs featuring solid fuel particles, but the reported results also provide insights into the corrosion in MSR designs where the uranium fuel is dissolved in the molten fluoride salt. Corrosion was observed to occur predominantly by de-alloying of Cr from the alloy surface and into the molten salt, with more pronounced attack occurring along the grain boundaries than in the bulk grains. The magnitude and the mechanisms of corrosion were different for corrosion tests performed in graphite and metallic capsules, a result warranting recognition given the coexistence of structural alloys and graphite in the molten salt medium in the MSR.
Versatile nanostructured processing strategy for bone grafting nanocomposites based on collagen fibrillogenesis
Advances in Applied Ceramics, 2009
ABSTRACT Strong bone-like nanocomposites of collagen type I and hydroxyapatite were prepared by c... more ABSTRACT Strong bone-like nanocomposites of collagen type I and hydroxyapatite were prepared by coupling the in situ synthesis, hybrid gel formation and subsequent dehydration consolidation. The calcium phosphate synthesis was initiated at 4°C in the concentrated collagen monomeric solutions. Under this condition collagen molecules inhibited the calcium phosphate uncontrollably rapid growth and the predominant collagen fibril aggregation was retarded. Elevating temperature induced collagen fibrillogenesis leading to the formation of elastic hybrid gels. The dehydration consolidation of the elastic gels gave rise to strong nanocomposites. The mechanical properties and bone-like characteristics of the prepared nanocomposites were explicated. The in situ formation of a hybrid gel together with its facile processing capability suggests the versatility of this biomimetic strategy either in fabricating different structural forms (films, scaffolds and monoliths) of bone grafts or in further inclusion of other biosubstance into the nanocomposites.
The use of molten salts as coolants, fuels, and tritium breeding blankets in the next generation ... more The use of molten salts as coolants, fuels, and tritium breeding blankets in the next generation of fission and fusion nuclear reactors benefits from furthering the characterization of the molecular structure of molten halide salts, paving the way to predictive capability of chemical and thermo-physical properties of molten salts. Due to its neutronic, chemical, and thermo-chemical properties, 2LiF−BeF2 is a candidate molten salt for several fusion and fission reactor designs. We perform neutron and X-ray total scattering measurements to determine the atomic structure of 2LiF−BeF2. We also perform ab-initio and neural network molecular dynamics simulations to predict the structure obtained by neutron and X-ray diffraction experiments. The use of machine learning provides improvements to the efficiency in predicting the structure at a longer length scales than is achievable with ab-initio simulations at significantly lower computational expense while retaining near ab-initio accuracy...
• Hastelloy N and 242, shows corrosion resistance to molten salt at nominal operating temperature... more • Hastelloy N and 242, shows corrosion resistance to molten salt at nominal operating temperatures. • Both diffusion welds and sheet material in Hastelloy N were corrosion tested in at 650, 700, and 850 • C for 200, 500, and 1000 h. • Thermal gradients and galvanic couples in the molten salts enhance corrosion rates. • Corrosion rates found were typically <10 mils per year.
The resurgence of the Molten-Salt Nuclear Reactors (MSR) creates interesting problems in molten-s... more The resurgence of the Molten-Salt Nuclear Reactors (MSR) creates interesting problems in molten-salt chemistry. As MSRs operate, the composition and physical properties of salts change because of fission and corrosion. Since Cr is the principal corrosion product and NaCl is a common constituent, we studied the atomic structure of molten NaCl-CrCl3. We found networks of CrCl3− 6 octahedra and an intermediate-range order with nonmonotonic temperature behavior in a remarkable agreement between measurements and ab initio simulations. Even though the corrosion results in minute quantities of dissolved Cr, the speciation of Cr could lead to changes in molten-salt properties in nuclear and solar salts. In particular, we found a much lower than expected melting temperature and a broad metastable liquid-solid coexistence phase. The availability of Cr isotopes with very different neutron-scattering properties makes Cr an ideal model multi-valent ion for experimental validation of new atomisti...
Recent developments in high-magnetic-field fusion systems have created large incentives to develo... more Recent developments in high-magnetic-field fusion systems have created large incentives to develop flibe (Li 2 BeF 4) salt fusion blankets that have four functions: (1) convert the high energy of fusion neutrons into heat for the power system, (2) convert lithium into tritium-the fusion fuel, (3) shield the magnets against radiation, and (4) cool the first wall that separates the plasma from the salt blanket. Flibe is the same coolant proposed for fluoride-salt-cooled high-temperature reactors that use clean flibe coolant and graphite-matrix coated-particle fuel. Flibe is also the coolant proposed for some molten salt reactors (MSRs) where the fuel is dissolved in the coolant. The multiple applications for flibe as a coolant create large incentives for cooperative fusion-fission programs for development of the underlying science, design tools, technology (pumps, instrumentation, salt purification, materials, tritium removal, etc.), and supply chains. Other high-temperature molten salts are being developed for alternative MSR systems and for advanced Gen-III concentrated solar power (CSP) systems. The overlapping characteristics of flibe salt with these other salt systems create significant incentives for cooperative fusion-fission-solar programs in multiple areas. We describe the fission and fusion flibe-cooled systems, what has created this synergism, what is different and the same between fission and fusion in terms of using flibe, and the common challenges. We review (1) the characteristics of flibe salts, (2) the status of the technology, (3) the options for tritium capture and control in the salt, heat exchangers, and secondary heat transfer loops, and (4) the coupling to power cycles with heat storage. The technology overlap between flibe systems and other high-temperature MSR and CSP salt systems is described. This defines where there are opportunities for cooperative programs across fission, fusion, and CSP salt programs.
The effects of ionizing radiation on materials often reduce to “bad news”. Radiation damage usual... more The effects of ionizing radiation on materials often reduce to “bad news”. Radiation damage usually leads to detrimental effects such as embrittlement, accelerated creep, phase instability, and radiation-altered corrosion. Here we report that proton irradiation decelerates intergranular corrosion of Ni-Cr alloys in molten fluoride salt at 650 °C. We demonstrate this by showing that the depth of intergranular voids resulting from Cr leaching into the salt is reduced by proton irradiation alone. Interstitial defects generated from irradiation enhance diffusion, more rapidly replenishing corrosion-injected vacancies with alloy constituents, thus playing the crucial role in decelerating corrosion. Our results show that irradiation can have a positive impact on materials performance, challenging our view that radiation damage usually results in negative effects.
Hastelloy N Ò , a nickel-based alloy, and 316 stainless steel are among the candidate structural ... more Hastelloy N Ò , a nickel-based alloy, and 316 stainless steel are among the candidate structural materials being considered for the construction of the molten salt reactor (MSR). Most of the proposed MSR concepts use molten fluoride salts as coolant which can be quite corrosive to structural alloys. The results of studies on the corrosion behavior of the two alloys in molten Li 2 BeF 4 (FLiBe) salt at 700°C are discussed. This salt is being considered as the primary coolant for MSR designs featuring solid fuel particles, but the reported results also provide insights into the corrosion in MSR designs where the uranium fuel is dissolved in the molten fluoride salt. Corrosion was observed to occur predominantly by de-alloying of Cr from the alloy surface and into the molten salt, with more pronounced attack occurring along the grain boundaries than in the bulk grains. The magnitude and the mechanisms of corrosion were different for corrosion tests performed in graphite and metallic capsules, a result warranting recognition given the coexistence of structural alloys and graphite in the molten salt medium in the MSR.
Versatile nanostructured processing strategy for bone grafting nanocomposites based on collagen fibrillogenesis
Advances in Applied Ceramics, 2009
ABSTRACT Strong bone-like nanocomposites of collagen type I and hydroxyapatite were prepared by c... more ABSTRACT Strong bone-like nanocomposites of collagen type I and hydroxyapatite were prepared by coupling the in situ synthesis, hybrid gel formation and subsequent dehydration consolidation. The calcium phosphate synthesis was initiated at 4°C in the concentrated collagen monomeric solutions. Under this condition collagen molecules inhibited the calcium phosphate uncontrollably rapid growth and the predominant collagen fibril aggregation was retarded. Elevating temperature induced collagen fibrillogenesis leading to the formation of elastic hybrid gels. The dehydration consolidation of the elastic gels gave rise to strong nanocomposites. The mechanical properties and bone-like characteristics of the prepared nanocomposites were explicated. The in situ formation of a hybrid gel together with its facile processing capability suggests the versatility of this biomimetic strategy either in fabricating different structural forms (films, scaffolds and monoliths) of bone grafts or in further inclusion of other biosubstance into the nanocomposites.
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Papers by Guiqiu Zheng