Method and System for the Production of Hydrogen at Reduced VHTR Outlet Temperatures

The Department of Energy and the Idaho National Laboratory are developing a Next Generation Nuclear Plant (NGNP) to serve as a demonstration of state-of-the-art nuclear technology. The purpose of the demonstration is two fold (1) efficient low cost energy generation and (2) hydrogen production. Although a next generation plant could be developed as a single-purpose facility dedicated to hydrogen production, early designs are expected to be dual purpose. While hydrogen production and advanced energy cycles are still in its early stages of development, research towards coupling a high temperature reactor with electrical generation and hydrogen production is under way. Many aspects of the NGNP must be researched and developed in order to make recommendations on the final design of the plant. Parameters such as working conditions, cycle components, working fluids, and power conversion unit configurations must be understood. The integrated system of a Very High Temperature Reactor (VHTR) and a High Temperature Steam Electrolysis (HTSE) hydrogen production plant is being investigated and this system, as it is currently envisioned, will produce hydrogen by utilizing a highly efficient VHTR with a VHTR outlet temperature of 900 C to supply the necessary energy and electricity to the HTSE unit. Though the combined system may produce hydrogen and electricity with high efficiency, the choices of materials that are suitable for use at 900 C are limited due to high-temperature strength, corrosion, and durability (creep) considerations. The lack of materials that are ASME (American Society of Mechanical Engineers) code-certified at these temperatures is also a problem, and is a barrier to commercial deployment. If the current system concept can be modified to produce hydrogen with comparable efficiency at lower temperatures, then the technical barriers related to materials selection and use might be eliminated, and the integrated system may have a much greater probability of succeeding at the commercial scale. This paper describes a means to reduce the outlet temperature of the VHTR to approximately 700 C while still maintaining plant high efficiency.