ابزار تجزیه و تحلیل سیستم با یک مدل سازی توربین گاز 2D برای بار گذرا HTGRS

This paper presents the operational performance and transient response of a high temperature gas-cooled reactor (HTGR) with an emphasis on the gas turbine through a two-dimensional approach. For its operational and transient simulation we use a GAMMA-T in which the system code, GAMMA, is coupled with the two-dimensional turbomachinery model. We also implement several models into the GAMMA-T: the reactor kinetics model, the bypass valve model, and the models of the core, the heat exchangers, the gas turbine, and the piping. The estimations of compressor and turbine performances are based on a two-dimensional axisymmetric throughflow method that is capable of predicting both the transient and steady-state behavior of the power conversion system (PCS). To demonstrate the code capability, we investigated the two representative transients of GTHTR300, which is a 600 MW direct cycle helium cooled reactor consisting of a prismatic block type core, a horizontal single-shaft configuration of turbomachinery, a recuperator, and a precooler: a loss of heat rejection transient corresponding to the failure of the precooler water supply, and a 30% load reduction transient from nominal operation with bypass control. The simulation results demonstrated the controllability and operational stability for the plant.

High temperature gas-cooled reactor (HTGR) designs have advantages in energy conversion efficiency mainly due to the closed Brayton cycle. The power conversion system (PCS) based on the direct helium turbine cycle is considered a promising choice because of its simplicity and high efficiency. In this configuration, the gas turbine performance in normal and off-design conditions has a major effect on the dynamic plant behavior. System analysis codes therefore need advanced capabilities for predicting the thermal-hydraulic behavior of the HTGR regarding the close connection between the gas turbine and the other components of the cycle. The dynamic analysis of closed cycle gas turbine plants dates back to the 1970s. The earlier integrated models used conventional turbomachinery performance maps to predict the control behavior of plants (Bammert and Krey, 1971, Hewing and Forster, 1977, Bardia, 1980, Yan, 1990 and Kullmann and Dams, 1996). The recent transient system codes were built with a fine description of the PCS components, but the turbomachinery models were still defined with their performance characteristic maps (Verkerk and Kikstra, 2003 and Tauveron et al., 2005). They reported that the off-design conditions could lead to appreciable errors due to limitations of the use of turbomachinery performance maps. Fisher et al. (2005) implemented a compressor model in the RELAP5-3D code, which also required the performance curves. Several studies have been made on accidental situations. In the event of a turbine deblading accident, a thermal-hydraulic study was performed using turbomachinery performance maps (Saez et al., 2006). Focusing on the post-surge and depressurization behavior, Tauveron et al. (2007) applied a one-dimensional axisymmetric turbomachinery model. Studies to investigate the HTGR behavior under extreme off-design operations have made noticeable progress. On the other hand, little attention has been paid to the development of a more detailed axial turbomachinery model for the transient analysis of PCS than the one-dimensional approach. For practical applications, more precise models are needed because the real flow in an axial-flow multi-stage gas turbine is inherently three-dimensional and exceedingly complex. It is necessary to simplify the flow as having an intermediate level of sophistication while considering the radial pressure gradient due to the lengthwise change of the streamline curvature radius in the gas turbine. Therefore, we have suggested a two-dimensional axisymmetric throughflow calculation to describe the axial turbomachinery in the PCS and incorporated the throughflow calculation tool into a transient system analysis code. Very few attempts have been made at the dynamic analysis of the plant through the two-dimensional axisymmetric turbomachinery model. In this paper, the design of the GTHTR300 by JAEA (Takizuka et al., 2004) is chosen for modeling and analysis. The GTHTR300 is a 600 MW direct cycle helium cooled reactor consisting of a prismatic block type core, a horizontal single-shaft configuration of turbomachinery, a recuperator, a precooler, and the piping. The dynamic models in the GAMMA-T code are described herein, and the operational performance and the representative transient response behavior are presented with a complete description of the modeling of each PCS component. Two transient thermal-hydraulic simulations are carried out for the plant: (a) the loss of heat rejection without a gas turbine trip; (b) a 30% load reduction with a bypass valve control.

We have simulated the steady-state and dynamic behaviors of a closed cycle helium-cooled reactor in the normal operating load transients. The gas turbine model based on the two-dimensional throughflow methodology was incorporated into the system analysis code, GAMMA-T. The reactor and the other PCS components were designed by one-dimensional thermal-hydraulic models. The system code was equipped with a reactivity control and bypass control models. The dynamic models were capable of describing the behavior of the whole plant in two cases: a loss of heat rejection transient corresponding to the failure of the precooler water supply, and a 30% load reduction transient from nominal operation. The core outlet temperature of 850 °C was maintained by the reactivity control. Although the operating conditions of the gas were modified by a stepwise increase of the precooler water temperature, the plant could continue to work through a transition between different power levels. The 30% load reduction was controlled by the bypass valve control and the compressor functioned as a brake for the shaft overspeed. It was found out that the operation of the particular type of bypass valve, located between the compressor outlet and the precooler outlet, could maintain the overall efficiency over 40% at 70–100% part-load conditions. The simulation results demonstrated the controllability and operational stability of the plant. We will continue to improve the GAMMA-T models by coupling them with the three-dimensional neutronics analysis code for VHTR.