(332c) Combined Cycle Power Conversion With Natural Gas Co-Firing, for the Pebble-Bed Fluoride-Salt Cooled, High-Temperature Nuclear Reactor (PB-FHR)

Combined Cycle Power Conversion with Natural Gas Co-Firing,
for the Pebble-Bed Fluoride-Salt Cooled, High-Temperature Nuclear Reactor (PB-FHR)

Charalampos Andreades, Raluca O. Scarlat, Per F. Peterson

AIChE Conference, November 2013, San Francisco

Nuclear Engineering Division (14), Sustainable Hybrid Energy Systems

The Fluoride-Salt-Cooled High-Temperature Reactor (FHR) is a Generation IV reactor technology now under development in the U.S. and China.  It is a pool type reactor that combines several technologies, namely passive decay heat removal and safety systems, graphite-matrix coated-particle fuel, fluoride salt coolant (flibe), and open-air Brayton cycle power conversion.  The FHR uses flibe as a coolant, a lithium fluoride and beryllium fluoride salt mixture, which has high melting (459°C) and boiling (1430°C) temperatures, and operating at nearly atmospheric pressure in the reactor primary coolant loop.  With structural materials such as 316 stainless steel or Alloy N, FHRs can deliver heat in the temperature range between 600°C and 700°C.  These characteristics allow for its coupling to a Brayton cycle.

UC Berkeley has been studying nuclear air-Brayton combined cycles (NACC) for application to FHR power conversion system.  The NACC provides several potential technical/operational as well as economic benefits. FHRs, as well as fluid-fueled Molten Salt Reactors (MSRs), appear to be unique in their capability to couple to a NACC power conversion system (PCS).  One of the most attractive reasons for using an open air Brayton cycle is that the major technology and components are commercially available and well developed for application to natural gas combined cycle (NGCC) power conversion. 

Another beneficial aspect of the open air Brayton cycle is the feasibility to use a conventional combined cycle configuration, with a Rankine bottoming cycle or other combined process heat application steam production, hydrogen production, advanced multi-effect distillation, etc.).  This also implies NACC thermal efficiencies in the range of 40-48% and increased power conversion efficiency compared to LWRs.  Furthermore, natural gas, hydrogen, or other fuels can be injected directly after the last nuclear heater stage for cofiring, which yields increased temperatures and power output for peaking operation.

The flexibility of NACC power conversion allows it to provide a wide range of grid support and process heat services. Two optimization goals for co-firing are to maximize peak power output in order during periods of high electricity prices, and to enable rapid power ramping rates, creating a flexible electricity source to provide spinning reserve and grid frequency control services.

The combination of an open air Brayton cycle to an FHR gives the possibility of a nuclear reactor to provide ancillary services to the independent system operator, such as peaking, load following, spinning reserve, and black start services, previously not possible by commercial reactors. This presentation provides a brief market survey of currently available commercial gas turbines, examines several parameters that are important in coupling a commercial gas turbine to nuclear heat source, suggests a possible system configuration to achieve it, and summarizes the modifications that must be made to gas-fired turbines in order for them to be used with nuclear heat and gas co-firing.