Comparative review of hydrogen production technologies for nuclear hybrid energy systems

Nuclear hybrid energy systems (NHES) have potential to capitalize on (1) producing multiple commodities, i.e. electricity and hydrogen as well as (2) allowing for electricity grid load following, with hydrogen production during low electricity prices. Using nuclear thermal energy and electricity (from the reactor itself) makes hydrogen production an economically attractive option. The reactor can continuously operate at full capacity, sending excess heat and electricity towards hydrogen production, which could either be sold or converted back to electricity using fuel cells at high price times. Several hydrogen production technologies exist, but in this study the focus is on processes that require heat and electricity. These candidates include alkaline water electrolysis, proton exchange membrane (PEM) electrolysis, solid oxide electrolysis cells (SOEC), thermochemical sulfur-iodine (S-I), calcium-bromide (Ca-Br) cycles, hybrid sulfur (HyS) and copper-chlorine (Cu-Cl) cycles. Each have different minimum temperature requirements which can be coupled to Generation III and IV reactor outlet temperatures: low (<300 degrees C), medium (<750 degrees C), and high (<950 degrees C). Energy input and material process flow diagrams were created for all technologies at compatible reactor temperatures and compared to the most common commercially operating hydrogen production method: steam methane reforming (SMR). Technology readiness levels (TRLs) and costs were also compared. The TRL of most systems is still below commercial development, and hydrogen productions costs are still too high to be economic without additional policy and/or other developments.