Power conversion system considerations for a high efficiency small modular nuclear gas turbine combined cycle power plant concept (NGTCC)

• Nuclear plant concept with very high temperature helium cooled reactor heat source.
• Helium gas turbine and supercritical steam turbine power conversion system.
• Modular plant concept power 180 MWe and projected efficiency 51.5 percent.
• Cogeneration option with electrical power plus steam supply for industrial users.
• Existing technology bases for reactor, gas and steam turbines, and steam generator.

The power conversion system (PCS) in the proposed small modular combined cycle nuclear gas turbine plant is based on the coupling of a non-intercooled topping helium Brayton direct closed-cycle gas turbine and a single-reheat supercritical steam Rankine bottoming cycle. The nuclear heat source (with a thermal rating of 350 MWt) is a helium cooled and graphite moderated very high temperature reactor (VHTR) embodying an assembly of prismatic fuel elements. Based on a reactor outlet (and gas turbine inlet) temperature of 95 °C, the module electrical power output is 180 MWe (50 and 130 MWe from the gas and steam turbines respectively) with an estimated plant efficiency of 51.5 percent. The design and development of the proposed nuclear gas turbine combined cycle (NGTCC) concept would benefit from established technology bases. With the inclusion of a process heat extraction module embodying a compact steam-to-steam re-boiler the proposed plant concept could operate in a cogeneration mode, namely generating electrical power plus providing a supply of uncontaminated process steam to various industrial users. This paper addresses projected HTR to VHTR plant evolution, thermodynamic cycle selection, plant performance, tentative arrangement of the combined cycle PCS, component design considerations and their technology bases, and major development requirements. The NGTCC is an advanced long-term helium cooled reactor concept, and a single module demonstration plant may be realizable by say circa 2030, this leading to commercial operation of multi-module plants, and paving the way for future very high temperature nuclear process heat plants in the middle decades of the 21st century.