Coupling nuclear and hydrogen-production technologies could enable affordable alternative to fossil fuel

Energy infrastructure of the future could look very different to the infrastructure we rely on today. Research by a team of experts from the National Nuclear Laboratory shows that powering hydrogen production using nuclear energy could be economically viable.

This research was published in the journal New Energy Exploitation and Application.

Mark Bankhead, Chemical Modeling Team Manager, explains the background to the research, “Hydrogen and hydrogen-derived alternative liquid fuels are a key enabler for the UK to reach net zero emissions by 2050. Nuclear power can be coupled to different hydrogen-producing technologies. To inform our strategy for demonstrating the value of these technologies by the 2030s, we developed a model that provides insight into their techno-economic performance.

“There are competitive advantages of thermochemical hydrogen production coupled with a High Temperature Gas-cooled Reactor (HTGR), and we know there is more work to do to optimize these technologies and realize the potential of this technology.”

A new way of determining efficiency and costs

In a new approach to determining the economics of these technologies, a ground-breaking mathematical model was constructed which coupled nuclear power to hydrogen-producing technology. The model allows different hydrogen production technologies to be coupled, which means that different scenarios can be compared.

The model was constructed in two parts. First, the physical and chemical processes of different hydrogen production technologies were modeled. This provided a novel method of determining the overall efficiency of these industrial processes by expressing the output of the model as units of hydrogen produced per unit of energy supplied. In the second part of the model, this measure of efficiency was fed into an economic model.

Kate Taylor, a process modeler at NNL, worked on the economic model, says, “In order to determine the selling price of hydrogen, the model combines the cost of building and operating a hydrogen plant with the cost of the electricity and/or heat needed to supply it.

“We also included estimates on how hydrogen-producing technology will improve, and how building a fleet of nuclear reactors will refine our knowledge of coupling nuclear plants to these technologies. We are predicting what will happen in the future based on our current knowledge of technology development. And the predictions are very encouraging.”

Testing different scenarios

Hydrogen can be produced using high temperature steam electrolysis which requires both heat and electricity. It can also be produced using a thermochemical cycle which only requires heat. In the modeling, both types of technology were coupled to a high temperature gas reactor, an advanced type of nuclear power.

The model showed that high temperature steam electrolysis could be a cost-effective way of producing hydrogen when coupled to a high temperature gas reactor, with a cost estimate of 1.24 to 2.14 £/kg, whereas, for a thermochemical cycle it is 0.89 to 2.88 £/kg.

Steam electrolysis is a more developed technology than any thermochemical cycle, which means that, not only is there less variation in the estimated cost, but deployment can happen sooner. Compared to other low-carbon energy production technologies that could also be coupled to hydrogen production plants, these results show that the costs involved with nuclear energy are competitive.

The model is an ideal starting point for comparing technologies. Christopher Connolly, a process modeler at NNL and lead author of the study, developed models of the physical and chemical processes. He explains how developments in hydrogen production technologies can improve the model because it relies on data that describes how molecules move about and interact with the materials used to produce hydrogen.

Connolly says, “Predicting the efficiency of hydrogen production means that you need to model the practical processes used to split water. Finding reliable data on the kinetics of some processes at the cutting edge of material property design can be a challenge and the technology is improving all the time.

“For example, when we looked at high temperature steam electrolysis, we needed to build a model of the electrolysis cells which use a solid oxide as the electrolyte. The solid oxide is typically made of yttria-stabilized zirconia, but variations of this oxide are used in different designs. Ultimately, the performance of the electrolyte depends on how well it is made.”

Predicting the future

Cost-effective production of hydrogen is just one advantage of nuclear technology. Although the study only modeled the efficiency of chemical and physical processes for hydrogen-production technology, there are other advantages in coupling these technologies to nuclear power, such as a high capacity to produce hydrogen, flexibility in sitting close to users, and the ability to scale-up deployment. Nuclear power also represents a reliable, non-intermittent power source which would reduce the requirement for buffer storage of hydrogen.

A high temperature gas reactor is already in development and a demonstrator is planned in the UK for the 2030s. In the interim, other types of nuclear technology could be coupled to a hydrogen production plant to help meet net zero targets.