Transient analysis of a direct cycle nuclear heated gas turbine plant with nitrogen coolant

This paper investigates the thermodynamic cycle compatibility of combining a modified commercial gas turbine with a prismatic High Temperature Gas Reactor (HTGR) with a nitrogen coolant. In-addition the paper investigates the transient response of the combined reactor and turbine combination against operational power transients for a variety of control methodologies. The analysis methodology utilises turbine gas dynamics, lumped thermal mass and a point reactor kinetic model built within the Matlab and Simulink modelling environment. Design point data from commercial gas turbine data sheets provide the key turbine gas dynamic parameters enabling transient performance estimates of output power coolant mass flow and heat transfer properties of the direct cycle reactor plant. The methods permit simple assessment of a variety of currently available gas turbine products for use within a nitrogen cooled direct cycle prismatic HTGR. The combination of a Siemens SGT 600 gas turbine with a ∼ 45MWth prismatic HTGR is illustrated and considered to have potential as an overall plant combination. The transient analysis explored a novel control approach where characteristics of both inventory and turbine bypass control features were combined, delivering both fast and proportional power control within a single control system, whilst maintaining high part load system efficiency. Furthermore, when combined with passive reactivity control based on the core negative temperature coefficient, the control method was shown to reduce overall core thermal transients experienced during power level changes. The proposed design illustrates the potential for minimising development risk associated with the direct cycle HTGR through direct use of current commercial gas turbine products, whilst using negative temperature coefficients for reactivity control and maintaining a simple turbine control system design.