Prof. Dr. André Maïsseu World Council of Nuclear Workers

XXI° CENTURY TIME FOR HYDROGEN ECONOMY Prof. Dr. André Maïsseu World Council of Nuclear Workers

Energy System Chain ServiceTechnologies TransformerTechnologies Services Currencies Sources What Nature Provides What People Want...  What Civilization Creates

Historical Perspective on the Age of Petroleum The hydrogen economy will define the state of the world by the middle of the 21st century

Why Hydrogen? ENVIRONMENT Preserve Natural Resources for Future Generations Reduce Air Pollution and Greenhouse Gases ENERGY Growing Demand for Electricity Long Term Supply Fuel Diversity – Reduced Risk ECONOMY Better utilize Oil and Gas (Too Valuable to Burn) Ability to Grow a Robust Economy Energy is Major Part of Western Economy Trade Oil Imports Challenge World Economic Growth

Why Hydrogen? CO2 from fossil fuels is forcing climate destabilization. Anthropogenic CO2 only slowed by extensive H2 only stopped with supremacy of H2 among chemical fuels. To eliminate CO2 emissions requires both Non-C sources & Non-C currencies. Only two Non-C currencies can, together, provide complete services: electricity and hydrogen. Only one Non-C sources can appease world energy hunger: nuclear energy

Land Transport Land Transportation Hay Sunlight Horse Agriculture Steam Locomotive Land Transportation Coal Coal fields Coal mine ~1840 Internal Combustion Automobile Land Transportation Gasoline Crude oil Oil refinery ~1910 Nuclear Energy Fuelcell Vehicles Land Transportation Hydrogen Electrolysis …+ ~2040

Hydrogen-Electricity Age CURRENCY Synergies • H2 can be stored in enormous quantities, Electricity cannot. • Electricity moves energy without material, H2 cannot. • H2 is chemical/material feedstock, Electricity is not. • Electricity can process & store information, H2 cannot. • H2 wins for long-distance transport on earth

Bridge to the hydrogen economy • Hydrogen fuel cells • Zero-emissions transportation fuel • Distributed energy opportunity • Large-scale, zero emissionshydrogen production is anenabling technology

NUCLEAR POWER NUCLEAR POWER H2 ELECTRICITY H2 ELECTRICITY Nuclear Power Services today and tomorrow

Basic methods for producing hydrogen • Water is the preferred hydrogen “fuel” • Electrolysis using off-peak power • High-temperature electrolysis • High-temperature thermo-chemical water splitting • Water dissociation over ceramic membranes at moderate temperatures

Basic methods for producing hydrogen Electrolysis is itself reasonably efficient, but not when the cost of electricity production required for the electrolysis is included. Thermochemical production is more direct and does not require immediate electricity, but instead requires very high temperatures (750 to 1000C). Currently nearly all hydrogen is produced from natural gas and this creates carbon dioxide emissions.

Basic methods for producing hydrogen Other methods for nuclear hydrogen production are possible : Using nuclear heat for steam reforming of natural gas. This is an energy-intensive process where a fraction of the natural gas is used to provide heat at temperatures of up to 900°C. Steam reforming of methane has carbon dioxide as a by-product, which defeats the purpose of using cleaner nuclear power to produce hydrogen. Nevertheless, all these processes can potentially be driven with waste heat from a G/VCR electrical power plant because the waste heat temperature is very high and meets most requirements for high-T H2 production.

Water dissociation over ceramic membranes at moderate temperatures

Water dissociation over ceramic membranes at moderate temperatures H2 Production from Water Dissociation Using Mixed Conducting Membrane

Water dissociation over ceramic membranes at moderate temperatures

High-Temperature Electrolysis Many direct methods are possible for producing H2 with the input of heat and water. In order to achieve reasonable production costs however, very high temperatures are required to ensure rapid chemical kinetics and high conversion efficiencies. Nuclear heat sources therefore begin to be attractive for electrolysis applications. The theoretical energy requirement for electrolytic decomposition of water at 25°C is the negative of the heat of combustion of hydrogen in the reaction, 2H2O (l)  2H2 + O2, ΔH = -ΔHcombustion = 285.83×103 kJ/mole. This is about 3.53 kW-hours per m3 of H2. The decomposition voltage V, required is given by, ΔH = -nFV Where n= number of electrons transferred per mole of H2O, F= Faraday’s constant (96 000 C). The minimum actual voltage is therefore 1.48V at 298.15 K. The theoretical minimum voltage is however determined by the Gibbs free energy of formation, which is ΔfG = 237.53kJ/mole, or 1.23V. The difference between actual and theoretical electrolysis voltage is termed the over-potential.

High-Temperature Electrolysis • Identified as abaseline process • High overall efficiencies • Demonstrated viability • Potential economic benefits of off-peak electricity • Less electricity used than in conventional electrolysis

High-Temperature Electrolysis However, not very many nuclear reactors can deliver heat at the minimum of 1000°C required for efficient high temperature electrolysis.

Thermochemical hydrogen production processes

Thermochemical hydrogen production processes Thermochemical production of H2 imposes certain requirements on the reactor chosen to supply the heat. For the S-I process temperatures of between 750 and 1000°C are required. For the Ca-Br process steam needs to be provided at ~750°C. The nuclear system must be sufficiently isolated from the chemical plant for safety reasons.

Calcium-Bromine Cycle • Identified as a lower priority baseline process • Relatively high overall efficiencies • Demonstrated viability • Significant process improvement opportunity • Lower temperature requirements than Sulfur-based cycles

Calcium-Bromine Cycle It’s advantage is that electrolysis is performed on HBr rather than water (H2O). Water is a very strongly bound molecule and therefore hard to split, so if hydrogen can be split from some weaker bound molecules then the potential for efficiency gains are considerable. An idealized version of the UT-3 Ca-Br process consists of the following steps. Slow water splitting with HBR formation, CaBr2(solid) + H2O (g) CaO + 2HBr, (730°C, ΔG = +210.76 kJ/mole) Oxygen formation exothermically, CaO (solid) + Br2(g) CaBr2 + ½O2, (550°C, ΔG = -77.71 kJ/mole) Bromine regeneration Fe3O4(solid) + 8HBr (g) 3Fe3 Br2 + 4H2O + Br2, (220°C, ΔG = +210.76 kJ/mole) Hydrogen formation from FeBr2, 3Fe3 Br2(solid) + 4H2O (g) Fe3O4 + 6HBr + H2, (650°C, ΔG = +134.72 kJ/mole)

Sulfur-Based Cycles • Identified as a baseline process • High overall efficiencies • Most extensively demonstrated thermochemical process • Least complex system • Increased viability based on number of process options

Sulfur Cycle Process Limitations(Overall Reaction: H2SO4 SO2 + H2O + ½O2) • Key high-temperature steps are equilibrium steps • Two step process H2SO4 SO3 + H2O  SO2 + H2O + 1/2 O2 • Second step (far right) is the high-temperature controlling step and requires the use of a catalyst • Challenges with sulfur cycles • High temperatures (e.g. 850ºC) drive reaction to the right but are at the limits of practical materials and high-temperature reactor technology • Lower temperature operation (e.g. 700 °C) results in limited dissociation of SO3 and low process efficiency via the following sequence of events: • Unreacted H2SO4 and reaction products are cooled • Components are separated • Unreacted H2SO4 is reheated • High internal recycle with high costs and lower efficiency

Sulfur-Iodine Cycle

Sulfur-Iodine Cycle There are three idealized steps in the I-S process. The first is formation of sulphuric acid an hydriodic acid. I2 + SO2 + 2H2O 2HI + H2SO4 (low temperature), sulphuric acid decompostion, H2SO4 H2O + SO2 + ½ O2 ( ~900°C–1000°C) and the H2-producing step 2HI  H2 + I2 (intermediate temperature, ~500°C) In each of these processes, the high-temperature, low-pressure endothermic (heat-absorbing) reaction is the thermal decomposition of sulfuric acid to produce oxygen: The difficulties in the sulfuric acid decomposition stem form the fact that the reaction kinetics are temperature limited, as the back reaction occurs at lower temperatures.

Sulfur-Iodine Cycle It’s advantage is the high efficiency of the hydrogen forming step, but it requires the highly corrosive chemical, sulphuric acid. Concerns have been raised about the desirability of having such chemicals near reactor plants.

Sulfur Oxide Decomposition System Design(SO2, O2, and H2O Separation Allows Driving the Reaction to Completion) Chemical Reactor (H2SO4 SO3 + H2O  SO2 + 1/2O2 + H2O) Inorganic Membrane Separation Hot Fluid SO2, O2, H2O SO3, SO2, O2, and H2O Feed H2SO4 SO3 H2O Catalytic Reactor Tube Inorganic Separations Membrane Cold Fluid Recycle SO3 (With some SO2, O2, and H2O) Blower Heat Single Tube SO3, SO2, O2, and H2O SO3 Catalyst SO2, H2O, O2 Westinghouse-Ispra Sulfur Process

Conceptual System For Idealized Iodine-Sulfur Inorganic Membrane Chemical Reactor Operating Temperature 650 to 750°) Catalyst Bed (2SO3 2SO2 + O2) Inorganic Membrane Separations Heat Feed Gas H2SO4 SO3 H2O Gaseous Reaction ProductsO2 H2O SO2 Reaction Zone with Removal of Reaction Products (Shift Equilibrium) Reaction Zone: Approach Equilibrium SO3, SO2, H2O, O2 Westinghouse-Ispra Sulfur Process

Summary In summary, the economics of H2 production strongly depends on the efficiency of the method used. Production efficiency can be defined as the energy content of the resulting H2 divided by the energy expended to produce the H2. Hydrogen production by electrolysis is relatively efficient (~80%). However, when this factor is combined with the electrical conversion efficiency, which ranges from approximately 34% (in current light-water reactors) to 50 % (for advanced systems), the overall efficiency would be approximately 25 to 40%. A significant capital investment in electrolytic cells is also required.

Summary For thermochemical approaches such as the iodine-sulfur process described previously, an overall efficiency of >50% has been projected. Combined-cycle (H2 and electricity) plants may have efficiencies of ~60%. All of the efficient, potentially low-capital-cost thermochemical processes require high temperatures.

Major Reactor/Hydrogen Interfaces

Estimated comparative fuel use and efficiency measures for selected next generation nuclear power systems(LWRs included for reference)

Summary Light water reactors are unsuitable for intensive industrial chemical process requirements. Advanced high temperature nuclear reactors are well suited for these applications and high temperature gas cooled reactors have often been proposed as suitable heat sources for coal and oil upgrading, co-processing and cogeneration.

Summary The proposed gas core reactor system would meet almost all the demands of an efficient and effective heat or electricity source for hydrogen production. Figure 7 illustrates conceptually the advantages of nuclear power for H2 production using the highest temperatures available for solid or liquid fueled reactors. Notably a G/VCR would be capable of providing additional heat at even higher temperatures than that shown in Figure 7, for example for single shaft gas turbine Brayton cycle operation. The combined cycle efficiency of the G/VCR-H2 production facility can therefore be as high as 50% when operated at full capacity.

Conceptual illustration of availability of G/VCR nuclear heat and matching to cogeneration of electricity and process heat for thermochemical hydrogen production. Not drawn is the potential for even higher temperature Brayton gas turbine electricity production

Advanced High-Temperature Reactor

A schematic of a concept for a possible high efficiency, environmentally clean, integrated nuclear power and chemical fuel production facility

CONCLUSION In principle gas core reactors might be prototyped and deployed for these exciting applications within a couple of decades. Realistically though, a considerable R&D effort needs to be expended before these ideas become a reality.

Prof. Dr. André Maïsseu World Council of Nuclear Workers