Reheat Air-Brayton Combined Cycle Power Conversion Off-Nominal and Transient Performance

Abstract

Because molten fluoride salts can deliver heat at temperatures above 600 °C, they can be used to couple nuclear and concentrating solar power heat sources to reheat air combined cycles (RACC). With the open-air configuration used in RACC power conversion, the ability to also inject natural gas or other fuel to boost power at times of high demand provides the electric grid with contingency and flexible capacity while also increasing revenues for the operator. This combination provides several distinct benefits over conventional stand-alone nuclear power plants and natural gas combined cycle and peaking plants. A companion paper discusses the necessary modifications and issues for coupling an external heat source to a conventional gas turbine and provides two baseline designs (derived from the GE 7EB and Alstom GT24). This paper discusses off-nominal operation, transient response, and start-up and shutdown using the GE 7EB gas turbine as the reference design.

Design Summary of the Mark-I Pebble-Bed, Fluoride Salt–Cooled, High-Temperature Reactor Commercial Power Plant

“…The design of the NACC was performed using GE's extensive technical literature, while performance was estimated using Thermoflow's THERMOFLEX ® , a commercial power cycle modeling tool. Detailed design and performance estimation studies under nominal and off-nominal conditions of the NACC are provided by Andreades et al 7,8 Another ability of the NACC is to decouple power conversion transients from the reactor due to the open cycle configuration. This reduces risks involved with lossof-load events, for example, as the reactor will not feel this transient.…”

“…Conventional NG safety standards are applied, as well as additional safety measures, e.g., double bleed and block valves in the NG supply lines, ventilation, and underground vaulted supply lines with controlled access, which are detailed in Ref. 8. Figure 2 provides an isometric view of a notional Mk1 single-unit arrangement.…”

Optimization of a decoupled combined cycle gas turbine integrated in a particle receiver solar power plant

“…Al-attab et al [8] provided an extensive review of the currently operating externally heated Brayton cycles and of the associated high temperature heat exchangers. Andreades et al [9], [10] proposed a design based on commercially available gas turbines (reheat-air Brayton combined cycle), aimed at solar or nuclear applications, with optional hybridization for peaking. Finally, Puppe et al [11] compared several cycles to be coupled with a pressurized air receiver, including a low-TIT combined cycle.…”

Ni Interlayer to Improve Low-Pressure Diffusion Bonding of 316L SS Press Fit Tube-to-Tubesheet Joints for Coiled Tube Gas Heaters

“…1, that supports the use of Brayton-cycle power conversion for advanced nuclear reactors. UCB has developed an initial main design to transfer heat from a low-pressure 700 C, fluoride-salt coolant (at approximately 0.1 MPa) to compressed air (at approximately 1.8 MPa), which is then expanded through a gas turbine to produce power [1][2][3]. UCB has also developed an alternative heat-exchanger design that uses supercritical carbon dioxide (S-CO 2 ) instead of air, with lowpressure (0.1 MPa) liquid sodium metal as the primary coolant; this design requires operation at higher pressures (up to 20 MPa and 550 C) [4].…”