Scientists from Utah State University, USA, integrated high-temperature steam electrolysis cell with the state-of-the-art nuclear power plant. Their objective was to evaluate the efficiency of combining nuclear generation and hydrogen production using the reactor energy to the maximum extent and without CO₂ emissions.
The pilot prototype was built based on the Natrium reactor of TerraPower and GE Hitachi companies. This reactor belongs to the sodium-cooled fast reactors, it operates under much higher temperatures than the traditional water-to-water plants. They use liquid sodium as a coolant providing for efficient heat exchange under low pressure. Such schemes allow for transferring redundant heat to the energy accumulation system operating on molten salt performing a buffer: it accumulates heat and then releases it to cover peak loads or to feed external processes including receiving hydrogen.
The researchers built a prototype of a Nuclear Hybrid Energy System, where reactor, heat accumulator and hydrogen electrolysis cell are combined in a single thermodynamic scheme. Such system allows for redistribution of the generated energy depending on the needs: during peak loads – releasing it into the grid, and during the time of lower demand – using it for hydrogen production turning the redundant power into fuel.
The high-temperature steam electrolysis cell is the key element of the hydrogen block. It is based on hard-oxidic cells – ceramic elements, where water steam under 850 °C is decomposed into hydrogen and oxygen. In these conditions, a portion of energy is supplied in the form of heat decreasing the electricity consumption approximately by one third and making the process much more efficient compared to traditional low-temperature water electrolysis.
The researchers reviewed three options of integrating Natrium reactor with steam electrolysis cell. In the first case, the heat emanating during hydrogen production was used for heating the feed water in the steam system of the reactor. It allowed to decrease the steam extraction from the turbines and to improve the total efficiency factor of the plant approximately by 0.9%. In the second case, the heat from hydrogen was used for the repeated heating of the steam after the turbine first stage, which provided for additional efficiency growth – up to 1.1 %. In the third scheme, the electrolysis cell was fed with steam directly from turbines without interim heat exchangers and molten salt. This solution made the design simpler and decreased the cost, while as the overall efficiency of “reactor + hydrogen” complex turned out 2-3 % higher vs the option without integration.
Though the obtained results cannot be called revolutionary ones, the research is important because it demonstrated a new engineering approach to nuclear energy applications. Even a slight growth of the efficiency factor given hundreds of MW capacity of the reactor means dozens of megawatts of additional useful energy. But it is even more important that such integration is shaping a new architecture of nuclear energy industry: new generation reactors may operate as multi-functional nuclear hybrid energy hubs capable of simultaneous electricity generation, heat accumulation and hydrogen production.
