Carbon recycle nuclear hydrogen carrier system for transportation field

Possibility of a carbon recycle hydrogen carrier system driven by nuclear power for transportation field was discussed. The hydrogen carrier system, which was zero carbon dioxide emission and small hydrogen compression work and explosion risk, was examined for fuel cell vehicles. The combination of the hydrogen carrier system with a high-temperature gas reactor was proposed. It was expected that the carrier system realized lower pressure and safe storage of hydrogen consisting with the similar energy efficiency of conventional water electrolysis hydrogen system. Carbon neutral bio-mass energy system and the carrier system were compared for the next generation vehicle energy system. Bio-mass energy had the limitation of quantity and would take small part of vehicle market in Japan. Nuclear assisted bio-mass hydrogen system could enhance yield of bio-fuels under carbon neutral. The carbon recycle nuclear hydrogen carrier system was expected to be applicable to the demand of much more larger number of vehicles because it was free from the limitation of bio-mass carbon quantity.     

South Africa's opportunity to maximise the role of nuclear power in a global hydrogen economy

Global concern for increased energy demand, increased cost of natural gas and petroleum, energy security and environmental degradation are leading to heightened interest in using nuclear energy and hydrogen to leverage existing hydrocarbon reserves. The wasteful use of hydrocarbons can be minimised by using nuclear as a source of energy and water as a source of hydrogen. Virtually all hydrogen today is produced from fossil fuels, which give rise to CO₂ emissions. Hydrogen can be cleanly produced from water (without CO₂ pollution) by using nuclear energy to generate the required electricity and/or process heat to split the water molecule. Once the clean hydrogen has been produced, it can be used as feedstock to fuel cell technologies, or in the nearer term as feedstock to a coal-to-liquids process to produce cleaner synthetic liquid fuels. Clean liquid fuels from coal - using hydrogen generated from nuclear energy - is an intermediate step for using hydrogen to reduce pollution in the transport sector; simultaneously addressing energy security concerns. Several promising water-splitting technologies have been identified. Thermo-chemical water-splitting and high-temperature steam electrolysis technologies require process temperatures in the range of 850 °C and higher for the efficient production of hydrogen. The pebble bed modular reactor (PBMR), under development in South Africa, is ideally suited to generate both high-temperature process heat and electricity for the production of hydrogen. This paper will discuss South Africa's opportunity to maximise the use of its nuclear technology and national resources in a global hydrogen economy.     

Calorimetric investigations on stoichiometric barium and uranium oxides

Heat capacities and enthalpy increments of barium uranates: BaU₂O₇(s), Ba₂U₃O₁₁(s), Ba_2.875UO_5.875(s) and Ba₃UO₆(s) were measured using a differential scanning calorimeter and a high-temperature Calvet calorimeter. The heat capacities and enthalpy increments were measured in the temperature range 126-304 K and 299-1011 K, respectively. A set of self consistent thermodynamic functions such as entropy, Gibbs energy function, heat capacity and Gibbs energy and enthalpy of formation values for BaU₂O₇(s), Ba₂U₃O₁₁(s), Ba_2.875UO_5.875(s) and Ba₃UO₆(s) have been computed for the first time using the data obtained in the present study and other available experimental data.     

Nuclear Characteristics of Molten-Salt-Cooled D-D Fusion Reactor Blankets

To consecutively decompose ¹⁴CO₂ into carbon (¹⁴C) through its reaction with Hz, an apparatus using microwave discharge and its conditioning were investigated. The reaction produces CO as an intermediate, and proceeds in the two steps of (1) “CO₂+H₂ → CO+H₂O” and (2) “CO+H₂+C_n → C_n+1+H₂O”, where C_n denotes the carbon already deposited on the wall of the discharge tube. Preliminary dispersion of carbon to the wall of the discharge tube by sputtering of a graphite particle was effective to promote the reaction. Two silica discharge tubes (6 mm O.D., 4 mm I.D., and 150 mm length each) were connected in series to proceed the former reaction in the first discharge tube and the latter one in the second one. When a 1:3 mixture of CO₂ and H₂ (total pressure 0.67kPa) was passed through the discharge tubes at a linear gas velocity of approximately 30mm/s and discharged for 60 h under microwave of 30–40 W supplied from two 2,450MHz power generators (200 W each), more than 90% of CO₂ was converted into CO in the 1st tube and about 23% of the CO was then decomposed into carbon in the 2nd tube. However, about 50% of the CO escaped from the tube without being decomposed, and about 0.5% and 1% of the carbon fed were hydrogenated into CH₄ and C₂H₂, respectively. The rest about 25% which was not confirmed was probably evacuated from the 2nd tube as microparticles of carbon. To completely decompose CO₂ into carbon, additional discharge tubes are necessary downstream of the 2nd tube.     

Radiocarbon AMS determination of the biogenic component in CO2 emitted from waste incineration

The thermal utilization of waste for energy production is gaining importance in European countries. Nevertheless, the combustion of waste leads to significant CO₂ emissions in the atmosphere which, depending on the fraction of biogenic and fossil materials, have to be only partially accounted for the national greenhouse gas inventory. For this reason the development of proper methodologies for the measurement of the biogenic fraction in the combusted waste is an active research field. In fact the determination of the radiocarbon concentration in the carbon dioxide stack emissions allows to have a direct indication of the biogenic component in the burned fuel. We present the results of the AMS radiocarbon analyses carried out on carbon dioxide sampled at the stack of three power plants located in Northern Italy burning natural gas, landfill biogas and SRF (Solid Recovered Fuel) derived from MSW (Municipal Solid Waste). The sampling apparatus and the applied processing protocols are described together with the calculation procedures used to determine, from the measured radiocarbon concentrations, the proportion of biogenic and fossil component in the flue gas and in the combusted fuel. The results confirm the high potentialities of this approach in the analysis of industrial CO₂ emissions.     

Enthalpy and Gibbs energy of formation of cerium dicarbide

The equilibrium CO pressure over the condensed phase region of CeO₂(s)-CeC₂(s)-C(s) was determined by adopting a method termed as the dynamic effusion MS method, which involves the measurement of the CO effusing out from the sample using a quadrupole mass spectrometer, even during carbothermic reduction of the oxide. The formation of oxicarbide has been ruled out. The Gibbs energies of the reaction, CeO₂(s)+4C(s)=CeC₂(s)+2CO(g), at various temperatures in the range 1350-1550 K were then determined from the equilibrium CO pressures. From the Gibbs energies of the reaction, the Gibbs energy of formation of CeC₂(s) at 298 K was derived. Similarly, from the data on the second and third-law enthalpies of the above reaction, the enthalpy of formation of CeC₂(s) at 298 K was calculated. The recommended Gibbs energy and enthalpy of formation of CeC₂(s) at 298 K are (103.0±6.0) and (120.1±11.0) kJ mol^{− 1}, respectively.     

Kinetic study of the UO2/C interaction by high-temperature mass spectrometry

For very high-temperature reactors (V)-HTR, one of Generation IV future systems, the high-level operating temperature of the fuel materials in normal and accidental conditions requires the prediction of the possible chemical interactions between the fuel component (UO_2±x) and the structural materials (C, SiC). To predict the thermo-mechanical behaviour of the TRi-ISOtropic (TRISO) particle, it is necessary to better understand the gaseous carbon oxides formation at the fuel-buffer interface that leads to the build up of the internal pressure. High equilibrium CO_(g) pressures resulting from the UO_2±x/C reaction are predicted using thermodynamic calculations. The kinetic mechanisms involved in this reaction that limit this pressure increase have to be determined by convenient experiments and associated models. Some of the reported data on the kinetics of CO_(g) formation due to the UO_2±x and carbon interaction have been reviewed. The discrepancies between the reaction mechanisms can be explained (i) by the different geometries and sample types and (ii) by the oxide stoichiometry and the flowing gas used during the experiments. Depending on these characteristics, the phenomena involved in CO_(g) formation can be of three different origins: interface, surface or diffusion. Using high-temperature mass spectrometry (HTMS), kinetic measurements of the CO_(g) and CO_2(g) species evolved during the interaction between UO_2±x and carbon were performed. The samples are pressed pellets consisting of a mixture of UO_2±x (60% molar) and carbon black (40% molar) powders. CO_(g) is the major product above 1200 K. Rates of the CO_(g) formation have been established taking into account the oxygen composition of the non-stoichiometric uranium dioxide and temperature. Results underline the upmost importance of kinetic factors for studying the CO_(g) pressure variation inside the TRISO particle.     

Reaction kinetics and the equilibrium state in the system CO2-CO-C under the action of fast electrons

The kinetics of reactions occurring in the system CO₂–CO–C under the action of fast electrons (200 keV) were studied under standard conditions. The temperature was varied within the range 25–400° C; pressure 200–600 mm Hg. The absorbed energy was equal to 3.0·10¹⁵ eV/(cm³· sec) at a current strength of 100 A. The decomposition of CO₂ in the presence of carbon is a zero order reaction, while the decomposition of CO is a first order reaction. The activation energies of both reactions are close to zero. The rate of decomposition of CO₂ and CO is a linear function of the radiation intensity. The steady-state concentration of CO, established in the system after prolonged irradiation, is independent of the radiation intensity, temperature of the reaction zone, and depends on the magnitude of the carbon surface.Translated from Atomnaya Énergiya, Vol. 18, No. 5, pp. 492–496, May, 1965     

Climate change gains more from nuclear substitution than from conservation

We show the massive reduction achievable, in both emissions and climate change impact, from enhanced nuclear energy use on the forecasts of future world energy use and its associated environmental impacts. A range encompassing the major scenarios for the World's energy demand have been analyzed using the latest version of the climate-modeling MAGICC/SCENGEN software (Version 4.1). We have updated and predicted the impacts of 80% substitution with CO₂-free sources (likely predominantly nuclear) for coal-fired electricity (by 2030) and for transportation fuel (by 2040). For transportation, hydrogen produced by CO₂-free sources would replace gasoline and diesel fuels. In this paper, to bracket the range of futures, we simply focus on two scenarios from the Intergovernmental Panel on Climate Change's (IPCC), one (A1FI) that is energy-profligate and one (B2) that is energy-conserving.The results show that, interestingly, projected average global temperatures for all scenarios are fairly similar until about 2035 (a further rise beyond the 1990 average temperature of +0.75 ± 0.1 K) regardless of energy usage and its sources. However, by 2050, the different IPCC scenarios diverge markedly. Understandably, A1FI is projected to have noticeably stronger effects than B2 on average global temperatures (about 0.3 K more in 2050) but the effect is much stronger over land at mid and high latitudes (up to almost 1 K more). What is most striking is that the substitution of CO₂-free sources gives projected average temperature rises in 2050 over key land areas (North America and China) that are very similar for the two energy-use scenarios—typically 1–1.5 K because A1FI's additional energy is predominantly supplied by nuclear. In contrast, projected rises with the unaltered cases are markedly different being about 2.5 K for A1FI and 1.5–2 K for B2. The projected changes in rainfall distribution show similar patterns, especially for the expected increases in higher latitudes.With the assumption of no additional policies for substitution of energy sources beyond 2040, temperature divergence between the two scenarios of relative energy profligacy or conservation grows in the latter half of the 21st century, even with substitution. However, the early substitution of nuclear energy and hydrogen appears to buy time and is not crucially dependent on severe, near-term curtailment of energy use. Near-term curtailment is too difficult to implement at a time of rapid industrialization of major emerging economies. Of course, proportionately larger deployments of CO₂-free energy sources are needed for more energy-intensive scenarios.Nuclear power must dominate as the source of CO₂-free energy since it is proven, dependable, available on a large scale, and economic. Social objections to nuclear energy in some countries and quarters are seen as well-meaning but misguided distractions from solving the energy and environmental crises that are now facing world sustainability. The time for real technical, social and political action is now.     

Enthalpy and Gibbs energy of formation of dysprosium dicarbide

The equilibrium CO(g) pressures have been determined over the univariant three-phase field DyO_1.5(s)-C(s)-DyC₂(s) by means of the dynamic effusion MS method, in the temperature range 1360-1590 K. The carbide phase was generated in situ by the carbothermic reduction of the oxide using a quadrupole mass spectrometer, the effusion pressure of carbon monoxide was monitored. The enthalpy of the carbothermic reduction reaction was calculated by second- and third-law methods. By combining the appropriate thermal functions and enthalpies of other constituents from standard thermodynamic tables, the enthalpy of formation of the dicarbide at 298 K has been calculated. The Gibbs energy of formation of the dicarbide in this temperature range has also been calculated. The recommended values of enthalpy and Gibbs energy of formation of DyC₂(s) at 298 K are −(131 ± 19) kJ mol⁻¹ and −(165 ± 6) kJ mol⁻¹, respectively.     

Proton elastic scattering differential cross-sections for C

Carbon depth profiling presents a strong analytical challenge for all the major ion beam analysis (IBA) techniques, with elastic backscattering spectroscopy (EBS) being widely implemented. In the past, the ¹²C(p,p)¹²C reaction has been successfully evaluated for proton beam energies up to 4.5 MeV. Currently, an attempt is being made to extend this evaluation to higher energies, namely up to E_p,lab = 7 MeV. There is a certain lack of available and/or coherent datasets in literature for these relatively high proton beam energies at backward angles, suitable for IBA. Moreover, the few existing datasets are in certain cases discrepant. Thus, in the present work, the differential cross-section of proton elastic scattering on carbon were measured between 140°and 170°, in steps of 10°, for the proton beam energy range between 2.7 and 7 MeV. The experimental results obtained, along with data from literature, were evaluated applying nuclear physics models. The evaluated results were benchmarked using a thick, mirror polished glassy carbon target at different beam energies and detector angles.     

Nuclear carbonization and gasification of biomass for effective removal of atmospheric CO2

By the process of carbonization of biomass a portion of carbon element in biomass is stabilized as solid carbon, and the remaining portion of carbon, which is the volatile product from carbonization, is converted by the subsequent gasification and conversion process to carbon-neutral synthetic fuels, which can replace the fossil derived fuels currently used.In these processes, nuclear energy can effectively be utilized for supplying energy, thus avoiding the CO₂ emission from any biomass or fossil combustion. By utilizing nuclear energy, most of the carbons in biomass are converted to either stabilized solid carbon or carbon-neutral fuels.Thus, significant amount of CO₂ can efficiently be removed from the atmosphere by processing a part of annual growth of biomass, which leads to the decrease of atmospheric CO₂ concentration.     

Epitaxial 3C-SiC nanocrystal formation at the SiO2/Si interface after carbon implantation and subsequent annealing in CO atmosphere

3C-SiC nanocrystallites were epitaxially formed on a single crystalline Si surface covered by a 150 nm thick SiO₂ capping layer after low dose carbon implantation and subsequent high temperature annealing in CO atmosphere. Carbon implantation is used to introduce nucleation sites by forming silicon–carbon clusters at the SiO₂/Si interface facilitating the growth of 3C-SiC nanocrystallites.     

HTR's role in process heat applications

Advanced high-temperature nuclear reactors create a number of new opportunities for nuclear process heat applications. These opportunities are based on the high-temperature heat available, smaller reactor sizes, and enhanced safety features that allow siting close to process plants. Major sources of value include the displacement of premium fuels and the elimination of CO₂ emissions from combustion of conventional fuels and their use to produce hydrogen. High value applications include steam production and cogeneration, steam methane reforming, and water splitting. Market entry by advanced high-temperature reactor technology is challenged by the evolution of nuclear licensing requirements in countries targeted for early applications, by the development of a customer base not familiar with nuclear technology and related issues, by convergence of oil industry and nuclear industry risk management, by development of public and government policy support, by resolution of nuclear waste and proliferation concerns, and by the development of new business entities and business models to support commercialization. New HTR designs may see a larger opportunity in process heat niche applications than in power given competition from larger advanced light water reactors. Technology development is required in many areas to enable these new applications, including the commercialization of new heat exchangers capable of operating at high temperatures and pressures, convective process reactors and suitable catalysts, water splitting system and component designs, and other process-side requirements. Key forces that will shape these markets include future fuel availability and pricing, implementation and monetization of CO₂ emission limits, and the formation of international energy and environmental policy that will support initiatives to provide the nuclear licensing frameworks and risk distribution needed to support private investment. This paper was developed based on a plenary session presentation at HTR-2006 which won Best Paper.     

Kinetics of the carbothermic reduction of a ThO2 + UO2 + C mixture to prepare (Th,U)C

Carbothermic reduction of mechanically mixed ThO₂ + UO₂2 + C compact to (Th, U)C has been studied in the temperature range between 1743 and 2043 K with emphasis on reaction kinetics. The rate-limiting step of this reaction was attributed to the diffusion of CO gas in the outermost layer of the reaction products. By X-ray diffraction, ThO₂ and UO₂ were found to react with graphite respectively to produce two nearly separate dicarbide phases, both of which then reacted with residual ThO₂ to form a monocarbide phase. An apparent activation energy of about 320 kJ mol⁻¹ was obtained for this carbothermic reduction. Such a high activation energy can be explained by the CO gas diffusion through micropores in that product layer, by taking into account the standard enthalpy changes of the related reactions to produce CO gas.     

X-ray impact induced desorption of gases from surfaces

Measurements of gases released from 302 stainless steel and gold surfaces before and after discharge cleaning were made in ultrahigh vacuum using X-rays with an energy distribution typical of a tungsten bremsstrahlung spectrum. Similar measurements were also made for Al₂O₃ surfaces which had not been discharge cleaned. For the non-discharge-cleaned surfaces of stainless steel, Al₂O₃, and gold the predominant gas species observed mass spectrometrically was CO₂. For some stainless steel and Al₂O₃ surfaces CO and O₂ were also readily observed. Mean quantum yields for CO, O₂ and CO₂ release from such stainless steel surfaces, for example, ranged from < 6 × 10^?5 to 9 × 10^?4 molecules per photons in the bremsstrahlung spectrum characteristic for 50 keV electron energy. After discharge cleaning a decrease in the mean quantum yields was observed for the stainless steel and gold surfaces.     

CO2 corrosion of IG-110 nuclear graphite studied by gas chromatography

The CO₂ corrosion behavior of IG-110 nuclear graphite has been investigated using the gas chromatography method which allows the continuous analysis of the CO₂/CO gas mixture at the outlet of the corrosion chamber. The effects of temperature and initial CO₂ concentration are studied based on the Arrhenius-type reaction model. From 745 to 995 °C, the Arrhenius curve shows a linear behavior. For higher temperatures, a non-linear behavior is observed. The activation energy is calculated as 210 kJ/mole and is independent of the initial CO₂ inlet concentrations of 10%, 14% and 17%. The corrosion behavior at 1145 °C, in the diffusion-controlled regime, has also been investigated. At this temperature, the interior of IG-110 graphite is severely attacked by CO₂, and the material's surface morphology is changed drastically. A measurement of the corrosion rate against corrosion time shows that the corrosion rate initially increases to a maximum value at a weight loss degree of 30%–35%, after which it begins to decline.     

Infrared study of astrophysical ice analogues irradiated by swift nickel ions

Water, carbon oxide, carbon dioxide, and ammonia ices are known to be pervasive constituents of the solar system and the interstellar medium. These ices and ice-covered surfaces are exposed to bombardment by energetic projectiles like photons, electrons, and ions. Laboratory experiments have been carried out to study the effects of such irradiation. However, there is a clear lack of information about the interaction of heavy ion components of solar/stellar wind and galactic cosmic rays (e.g. Fe) with ices in the keV to GeV energy range. The objective of this work is to study the effects produced in astrophysical ices by highly charged nickel ions at relatively high energy (∼50-500 MeV) in the electronic energy loss regime, and to compare them with those produced by protons, photons, and electrons. Our results for CO₂ and CO indicate that sputtering induced by heavy ions can be an important mechanism to desorb molecules in astrophysical environments.     

Recovery of 14C from Graphite Moderator of Gas-Cooled Reactor (GCR)

The chemical exchange method of carbon isotopes between CO₂ and carbamate was applied to the recovery of ¹⁴C from 1,6001 graphite moderator of a gas-cooled reactor (GCR), Tokai-1, and the dimensions of ¹⁴C-enrichment process were evaluated numerically. Applicability of two processes with different operation modes, continuous process and batch process, was discussed under the conditions that the concentration of ¹⁴CO₂ in the stripped flow corresponding to 99% of feed CO² is less than the environmental standard.

For the continuous process using 2mol/l diethylamine (DEA)-octane solution as a working fluid at—20°C and 0.2 MPa, the column dimensions were evaluated as 3.2 m in diameter and 5.7 m in height in the case of operating period of 20 yr. For the batch process using 4 mol/l DEA-octane solution, the column dimensions were comparable to those of continuous process, when the process was operated at the rate of 4 batch/month under the conditions of—20°C and 0.3 MPa. From these results, it is concluded that the CO2/carbamate exchange method is applicable to the recovery of ¹⁴C from irradiated graphite. However, the batch process has serious disadvantages, such as large energy consumption to maintain the top reservoir at low temperature and the generation of a large quantity of secondary wastes. At the present stage, the continuous process should be selected for the practical process design.     

Experimental investigation of reaction behavior between carbon dioxide and liquid sodium

Reaction behavior of carbon dioxide (CO₂) with a liquid sodium pool was experimentally investigated to understand the consequences of boundary tube failure in a sodium-CO₂ heat exchanger. In this study, two kinds of experiments were carried out to investigate the reaction behavior.In one experiment, about 1-5 g of liquid sodium pool were poured into flowing CO₂ to obtain the information mainly about the thermo-chemical conditions to initiate the reaction and the chemical constituents of reaction products. During the experiment, visual observation was made using video-camera and the temperature change of the sodium pool and near the surface was measured by thermocouples. The experimental parameters were the sodium pool diameter, the initial temperature of sodium and CO₂, the CO₂ flow direction against pool surface, and the initial moisture concentration in CO₂. The solid products of sodium-CO₂ reaction were sampled and analyzed by X-ray diffraction (XRD), energy dispersion X-ray analysis (EDX), total organic carbon analysis (TOC), and chemical analysis. The reaction gas products were also sampled and analyzed by gas chromatography.In the other experiment, CO₂ was injected into about 200 g of liquid sodium pool to simulate the boundary failure in the sodium-CO₂ heat exchanger. The CO₂ was fed through a helical coil-type tube dipped into the pool to adjust the temperature to the sodium pool temperature, and injected upward into the pool from a pool bottom using a nozzle attached at the end-side of the tube. The experimental parameters were the initial temperature of sodium, the diameter of the nozzle, the flow rate and the injection time of CO₂. The temperature change of sodium pool and the cover gas was measured by thermocouples during the experiment, and the reaction products were sampled and analyzed by the same manner as in the former experiments after the experiment.From these experiments, it became clear that the exothermic reaction occurred above a threshold temperature, and useful and indispensable information such as the resulting temperature and pressure rise and the behavior of solid reaction products in the pool was obtained to evaluate the consequences of boundary tube failure incident in a sodium-CO₂ heat exchanger.