The U.S. Department of Energy and Idaho National Laboratory are developing a next-generation nuclear plant, very high temperature gas-cooled reactor (VHTR) to serve as a demonstration of state-of-the-art nuclear technology. The purpose of the demonstration is twofold: (a) efficient low-cost energy generation and (b) hydrogen production. While hydrogen production and advanced energy cycles are still in the early stages of development, research toward coupling VHTR, electrical generation, and hydrogen production is under way.

This technical note includes the coupling of a VHTR with a power conversion unit. One of the power conversion configurations in the coupled plant is a combined Brayton cycle and Rankine cycle. This configuration uses a mixture of helium and nitrogen that allows the use of modified gas-turbine technology, including the same design techniques, material, and testing facilities used for conventional air gas turbines, to be used for the VHTR electricity production application. Exhaust heat from the turbine is transferred to a heat exchanger where the transferred heat is used to generate steam for a Rankine cycle.The study was focused on the verification of the steam generator model and comparisons of results from HYSYS and RELAP5-3D. This technical note concludes that the overall results are in good agreement despite the differences in size of different flow regime lengths. The overall heat transfer behavior deviated within ~2.1%, and exit temperatures and temperature drops across the steam generator also show reasonable agreement with <5.1% difference between the two methods.