The Role of Generation IV Nuclear Reactors in the Canada’s Hydrogen Economy

Coined by John Bockris in 1970, the hydrogen economy is a proposed conceptual solution to reducing, or even eliminating, society’s dependence on fossil fuels. With developments in use of hydrogen as an energy carrier for stationary and portable applications, as well as for vehicles, the hydrogen economy is becoming more of a reality. These applications involve the inputs of hydrogen gas and oxygen gas to provide electricity, with only heat and water vapour as outputs. Hydrogen fuel cells have the potential to replace electric battery systems as a less toxic alternative, with the additional advantage of a long range in regards to automotive applications. However, while the use of hydrogen in fuel cells may be a clean process, the life cycle of hydrogen energy cannot be truly emission free without a clean method for producing hydrogen.

With steam methane reforming as the primary method for producing hydrogen, much research and development is being done on finding clean alternatives. Electrolysis in conjunction of renewable energy systems is the main proposed alternative, though there are concerns about the inefficiencies that arise from using the electricity for hydrogen production rather than directly for grid applications. The use of nuclear “waste heat” in conjunction with a thermochemical cycle is another method, and one that has been receiving a great deal of attention worldwide.

The Cooper-Chlorine thermochemical cycle, widely seen to be the most promising one in development, only requires temperatures up to 530°C for the decomposition of water into oxygen and hydrogen gases, as opposed to the temperatures of over 2000°C that would be needed without the use of a thermochemical cycle.. With the recovery and reusing of the copper and chlorine in this closed cycle, the process is clean and relatively cheap to operate. UOIT’s Clean Energy Research Lab currently conducts research on many aspects of the cycle.

The Sulfur-Iodine thermochemical cycle is also a promising method of hydrogen production. Like the Copper-Chlorine cycle, this cycle is clean as it recycles the sulfur and iodine components. It requires temperatures as high as 850°C for operation. While the temperature requirement is higher than that for the copper-chlorine cycle, this cycle still has the potential to be a clean, competitive hydrogen production method.

Both cycles have the potential to be coupled with a nuclear reactor to make use of its “waste heat” given the past and prospective advancements in Canada’s nuclear industry. Canada has an established nuclear industry, and is known worldwide for the Canadian Deuterium (CANDU) nuclear reactor. The history of nuclear power starts with the development of first generation prototype reactors from 1950-1970. From 1970 to 1990 came commercial second generation reactors, including Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) builds that are familiar in the industry today, as well as CANDU reactors. In the 1990’s third generation reactors emerged. The Enhanced CANDU 6 Reactor is part of this generation, with the Advanced CANDU Reactor (ACR) being part of Generation III+.

Currently in develop are concepts of 4th generation reactors. Like the Hydrogen Economy, Generation IV reactors are still a long term plan, but they have the potential to play a role in helping to finally achieve clean, large-scale hydrogen production.  As described above, a great deal of thermal energy input is required for nuclear water splitting, even with the use of a thermochemical cycle. The current Enhanced CANDU 6 reactors have an outlet temperature of only 310°, so it is important to look at what the future of nuclear power could provide for the advancement of clean hydrogen production.

Going forward, there are international efforts being made to bring Generation IV reactors beyond the conceptual stage, with the ultimate objective to enhance the safety and performance of nuclear power, and well as minimizing radioactive waste and maximizing the lifespan of the reactor. There are six concepts selected by the Generation IV International Forum (GIF), with goals to have at least one design certified by the year 2030. These concepts include the Molten Salt Reactor (MSR), Sodium Cooled Fast Reactor (SFR), Lead Cooled Fast Reactor (LFR), Gas Cooled Fast Reactor (GFR), the Very High Temperature Reactor (VHTR) and the Supercritical Water Cooled Reactor (SCWR).

Molten Salt Reactor (MSR)

The Molten Salt Reactor uses a circulating mixture of sodium, zirconium, and uranium fluorides as fuel, which flows through graphite core channels. This reactor has an outlet temperature of 700-800°C, making it a potential choice to couple with a hydrogen generation plant. It can also be designed as a thermal breeder, allowing for more efficient use of fuel and minimization of nuclear waste.

Sodium Cooled Fast Reactor (SFR)

Using sodium for cooling and a mixture of uranium and plutonium as fuel and a fast neutron spectrum, this reactor is designed for more efficient use of fuel, with improved management of waste. However, with an outlet temperature of only up to 550°C, this reactor is not a suitable choice for  coupling with a hydrogen generation plant as other reactors, and is much better suited for only electricity applications. It is expected to be ready for deployment by 2020.

Lead Cooled Fast Reactor (LFR)

Just like the SFR, the Lead Cooled Fast Reactor features a fast neutron spectrum. Using lead, or lead-bismuth eutectic as coolant, reactor makes efficient use of the fertile uranium is uses as fuel. While its outlet temperatures are typically under 600°C, it can be modified to provide outlet temperatures of up to 800°C with the use of advanced materials. It is possibly going to be ready for deployment by 2025.

Gas Cooled Fast Reactors (GCR)

Also featuring a fast-neutron spectrum, this reactor is cooled by helium gas and has several options for fueling, such as composite ceramic fuel and advanced fuel particles. The high outlet temperature of 850°C makes the GCR an excellent choice for coupling with hydrogen generation. Like the other two fast reactors, waste management is improved through this reactor design. It is likely to be ready for demonstration by 2020.

Very-High-Temperature Reactor (VHTR)

The ideal reactor for hydrogen generation is the Very-High-Temperature Reactor, a helium cooled reactor moderated by graphite with a thermal neutron spectrum. With an outlet temperature of 1000°C, it generates more than enough heat for an iodine-sulfur thermochemical cycle for hydrogen production.  It is expected to be ready for deployment by 2020.

Supercritical Water Reactor (SCWR)

The SCWR is a water-cooled reactor with the pressures and temperatures of water above its critical point of 22.1MPa and 374°. Supercritical fossil fuels are already a proven technology, and the merging of such technologies with advanced water-cooled nuclear reactor technologies offers the potential for a very high efficiency (up to 50%), as well as potential for hydrogen production. It is targeted to be ready for demonstration for 2022.

A CANDU Supercritical Reactor is also under consideration, with a pressure of 25MPa and a temperature of 625°C, moderated by heavy water. It also has the advantage of adapted to feature a fast neutron spectrum.

In conclusion, all Generation IV reactors have significant design concerns that must be addressed, such as corrosion or pressure tube burst, before they can be deployed as stand-alone power plants, let alone in a coupling with a thermochemical cycle to produce hydrogen. However, the on-going research into both hydrogen generation methods and Generation IV nuclear reactors is very exciting, and given Canada’s history in nuclear technology and interest in developing hydrogen technology, it will be interesting to see the possible intersection Generation IV Reactor advancements could have with hydrogen production advancements in Canada.

**All diagrams of 4^th Generation Nuclear Reactors from the Generation IV International Forum™ website: gen-4.org