Making the transition from a fossil fuel to a hydrogen economy is, to some, a long way off. However, research programmes in the USA are showing that the hydrogen future is a lot closer than you might think.
Some observers say a hydrogen-based economy is around the corner. Others say it might take a bit longer – say, another 15 years to wean ourselves away from the fossil fuel diet. But most agree a hydrogen-based economy is on its way, and that we will soon depend on fuel cells – not internal combustion engines – to power our homes and vehicles.
In fact, several nations – including the United Kingdom, United States, Iceland, Italy, Canada, India, Japan, Singapore, China, and Australia – announced last year that they intend to use advanced stationary and mobile fuel cell systems to shift from a fossil fuel economy to an emissions-free hydrogen economy.
If we are to embrace this new economy, we need to learn to produce enough fuel-grade hydrogen using several optional production methods that consider upfront costs, economics, carrier availability, political priorities, and public stakeholder considerations.
Large-scale power plants – including nuclear reactors that emit zero greenhouse gases into the atmosphere – will be needed to produce significant quantities of clean, fuel-grade hydrogen.
There are several proven methods to produce fuel-grade hydrogen, according to the US Department of Energy (DOE), including: steam methane reforming, high temperature electrolysis, and thermo-chemical water splitting.
The lead cooled fast reactor operation process
Economic factors, of course, will largely determine what hydrogen production methods – and what power sources are eventually chosen.
Operators currently produce 96-98 per cent of the world’s hydrogen using the steam methane reforming process.
This method passes natural gas (i.e., methane and other hydrocarbons) and steam over a nickel catalyst to produce hydrogen and subsequent carbon dioxide. While this is the most economical method of producing hydrogen today, the process has two major drawbacks:
- Its economics are tied to the cost of natural gas
- For each ton of hydrogen produced, approximately 7 t of carbon dioxide are released into the atmosphere.
Operators can use nuclear reactors to provide requisite heat to facilitate this method. This would reduce natural gas usage and carbon dioxide emissions.
Electrolysis involves passing an electric current through water, thereby splitting water molecules into hydrogen at the cathode (+) and oxygen at the anode (-). This method tends to function at a relatively low efficiency rate of 24 to 35 per cent, thus making the resulting hydrogen too expensive for large-scale applications.
High-temperature steam electrolysis (a variation of conventional electrolysis) uses heat instead of electricity to provide some of the energy needed to split water, thereby increasing the overall efficiency of the process to approximately 50 per cent.
Nuclear reactor operators might choose to use power produced during off-peak hours to provide the electric current required for the electrolysis process or the steam required for high temperature steam electrolysis. Either approach could result in the production of hydrogen without the use of fossil fuels or the release of greenhouse gases.
Thermo-chemical water splitting uses chemicals and heat in multiple steps to divide water into its component parts of hydrogen and oxygen at overall efficiency rates of 50-60 per cent.
Since hydrogen fuels will probably not be required for 15 years, many observers believe that Generation IV high temperature gas nuclear reactors – ones that operate at up to 1000 ºC – and the thermo chemical water-splitting method will be the most appropriate techniques to produce large quantities of hydrogen.
The thermo-chemical process, though, brings with it several distinct challenges. For example, system materials must be capable of supporting high operating temperatures and withstanding extremely corrosive environments.
Last year, the US DOE linked its “Generation IV Nuclear Reactor” programme with its “Nuclear Hydrogen Initiative.” These programmes aim to demonstrate efficient and economic commercial-scale hydrogen production via nuclear power no later than 2015.
The Gen IV Program is an international effort that has evaluated over 100 prospective systems. Gen IV R&D programmes will give engineers the opportunity to design materials that will support high temperature reactor operations needed to produce high quality hydrogen fuels at competitive prices.
To promote hydrogen production, Gen IV researchers highlighted three prospective reactor systems: “very high temperature (VHTR)”, “advanced gas-cooled”, or “liquid metal-cooled”.
Gen IV researchers recommended building a 600 MW VHTR concept reactor. This unit would feature a helium-cooled core based on either the prismatic block or pebble-bed fuel. The VHTR would have coolant outlet temperatures above 1000 ºC to foster highly efficient electricity production and hydrogen production via high-temperature thermo-chemical water-splitting.
As planned, it would operate at an efficiency of over 50 per cent and produce over 200 t of hydrogen per day. (This reactor would also be capable of producing hydrogen via high-temperature steam electrolysis if that process proves preferable.)
The VHTR would require significant advances in fuel performance and high-temperature materials, as well as high-temperature alloys, fiber-reinforced ceramics, or composite materials.
The DOE plans to target the VHTR System for near-term deployment. Gen IV Program participants also recommended developing a 288 MW GFR concept reactor. This unit would feature a fast neutron spectrum and closed fuel cycle for efficient management of actinides and conversion of fertile uranium.
Reactor capacity would include economical hydrogen production, electricity generation, and actinide management.
Core configurations would be based on pin- or plate-based fuel assemblies or prismatic blocks. The GFR system would be sustainable from a fuels perspective far into the future because of its closed fuel cycle and actinide management capacity.
The GFR would require significant advances in fuels and materials for high-temperature service in a fast reactor spectrum, as well as a robust design to address safety issues during off-normal conditions, and fuel recycle technology. Certain players (including Entergy Nuclear, Inc.) have considered using proven high temperature gas reactor technologies to generate electricity and hydrogen fuels.
Currently, there are 18 gas-cooled reactors and 14 advanced gas-cooled reactors active in the UK. Further, two such decommissioned reactors (Fort St. Vrain) and Peach Bottom Unit 1 (a 40 MW experimental high temperature helium-cooled and graphite-moderated reactor) operated in the US.
While these gas reactors are sharply different from forthcoming Gen IV units, lessons learned from their operation histories will complement Gen IV R&D.
Lead-cooled fast reactor
As proposed, an LFR system could promote hydrogen and electricity production. This system would be sized between 50-1200 MW with a reactor outlet temperature between 550-800ºC. It would feature a lead or lead/bismuth eutectic liquid-metal-cooled reactor cooled by natural convection.
It would also feature proliferation-resistant qualities, a fast neutron spectrum, a closed fuel cycle for efficient actinide management and conversion of fertile uranium, and a long-life core (up to 30 years).
The gas cooled fast reactor operation process
The LFR design would require significant advances in materials to serve in a corrosive, high-temperature environment.
The DOE has proposed building a prototype high temperature nuclear energy system at its Idaho National Laboratory. As planned, this system will produce hydrogen fuel, demonstrate advanced fuel cycle technologies, and promote Gen IV objectives.
In fact, in April 2003, the DOE announced it would award contracts to support these initiatives. (Entergy has announced its interest in participating in this programme.)
Energy companies, federal agencies, political leaders, trade associations, environmental advocates, and research institutions have expressed keen interest in shifting from a fossil fuel-based economy to a hydrogen-based economy.
To produce the large quantities of hydrogen fuels needed to support such a system in the near-term, we will need to link advanced utility-grade power plants with hydrogen production methods. Nuclear systems offer promising technologies to produce this fuel without adding residual greenhouse gases to the environment.
“We believe that the two biggest problems facing energy companies today involves doing something about climate change and the over-dependency on foreign oil and gas,” says Kenneth Hughey, senior manager of business development with Entergy Nuclear. “To address both of these issues, we must find a source of non-emitting energy. Using non-emitting nuclear energy to produce non-emitting, fuel-grade hydrogen can do just that – produce large quantities of clean energy.”
Using nuclear power to foster a hydrogen economy could also add value to a desirable commodity in the nation’s capital and help unite organizations that have traditionally been at loggerheads. “The facts are clear – nuclear energy is the only high density power source that does not emit greenhouse gases. Nuclear is environmentally friendly, and we should be more closely allied with other environmentally focused organizations,” said Jack Brons, Assistant to the President at the Nuclear Energy Institute.
“Even though a number of organizations – such as the African American Environmentalist Association – have come out in support of nuclear energy, many other organizations that band together under the environmentalist umbrella have traditionally spoken against nuclear energy,” Brons explained.
“Because building a hydrogen economy will require lengthy ramp-up, this period might afford a ‘coming-together’ opportunity in which there is recognition that we share a vision for a cleaner world where hydrogen plays a vital role.”