پیاده سازی مستقیم یک ابزار توربین گاز هلیوم جریان محوری در یک ابزار تجزیه و تحلیل سیستم برای HTGRs

This study concerns the development of dynamic models for a high-temperature gas-cooled reactor (HTGR) through direct implementation of a gas turbine analysis code with a transient analysis code. We have developed a streamline curvature analysis code based on the Newton–Raphson numerical application (SANA) to analyze the off-design performance of helium gas turbines under conditions of normal operation. The SANA code performs a detailed two-dimensional analysis by means of throughflow calculation with allowances for losses in axial-flow multistage compressors and turbines. To evaluate the performance in the steady-state and load transient of HTGRs, we developed GAMMA-T by implementing SANA in the transient system code, GAMMA, which is a multidimensional, multicomponent analysis tool for HTGRs. The reactor, heat exchangers, and connecting pipes were designed with a one-dimensional thermal–hydraulic model that uses the GAMMA code. We assessed GAMMA-T by comparing its results with the steady-state results of the GTHTR300 of JAEA. We concluded that the results are in good agreement, including the results of the vessel cooling bypass flow and the turbine cooling flow.

Current high-temperature gas-cooled reactors (HTGRs) are mostly based on a Brayton cycle with helium gas as the working fluid. The thermodynamic performance of axial-flow multistage helium gas turbines is of critical concern because the performance has a major effect on the overall efficiency and transient behavior of HTGRs. Thus, system analysis codes need advanced capabilities for predicting the dynamic behavior of a plant. To deal with the steady-state and transient analysis of HTGRs, gas turbine performance characteristics are required over a wide range of operating conditions. Conventionally, gas turbine design companies provide off-design performance maps. Recalculated off-design performance maps are needed for accurate transient analysis whenever a gas turbine design is changed for the optimization of the overall design conditions. The gas turbine performance maps are usually implemented in the system analysis code as a series of tables or correlations (Verkerk and Kikstra, 2003). Using these methods, we can see that the potential of interpolation errors is due to the nonlinearity in the efficiency curves (Fisher et al., 2005). Although the design of modern turbomachinery relies heavily on CFD, the task of performing full calculations for a three-dimensional flow in a multistage gas turbine is too time-consuming for routine analysis (Horlock and Denton, 2005). Thus, the CFD method is unsuitable for predicting of a long transient of a power conversion system (PCS). Tauveron et al. (2007) developed a one-dimensional approach by solving Navier–Stokes equations as a simplification of a complex three-dimensional flow to describe the compressor and turbine behavior. The streamlines change radii along the stages in a typical multistage axial-flow gas turbine, and this lengthwise change in radius creates an additional pressure gradient that acts on the flow (Korakianitis and Zou, 1992). The one-dimensional axisymmetric approach can be used for preliminary considerations of the compressor or turbine; however, it does not take into effect this additional pressure gradient from the streamwise change of the streamline curvature. On the other hand, a two-dimensional throughflow calculation is simplified to a suitable level of sophistication and this approach takes account of the radial pressure gradient of real flows in gas turbines. The throughflow analysis method can deal with multistage gas turbines and provide enough reliable information to enable us to proceed with simple and effective changes to the design within a short time scale; it is known that CPU time of the throughflow analysis is a few seconds using a typical PC. Furthermore, the code can be coupled with the system code fairly easily and only a short computation time is needed to run the coupled code for the transient analysis. We therefore suggest an alternative way of estimating the gas turbine performance in steady-state and transient operations under normal conditions. In this approach, we use a two-dimensional axisymmetric throughflow method for thermodynamic analysis of a flow in helium gas turbines and then model other PCS components one-dimensionally, except for the gas turbines. The SANA code performs a streamline curvature analysis, and the off-design performance of the gas turbine is incorporated into a transient system code by direct implementation. In this study, the implementation of gas turbine performances and the one-dimensional modeling of other PCS components were performed in the GAMMA code (Lim and No, 2006) which was originally developed for the purpose of analyzing postulated accidents in HTGRs. We compared the steady-state simulation results of the open literature data of the JAEA GTHTR300 design (Takizuka et al., 2004) because of the detailed information of the gas turbine. The design parameters of the GTHTR300 plant are presented in Table 1.

We have presented a steady-state PCS simulation of a HTGR with a helium working fluid under conditions of normal operation. To illustrate the performance of the dynamic model, we applied it to the GTHTR300 design of JAEA. The SANA code performs a two-dimensional throughflow analysis by incorporating industry-standard loss models for multistage axial-flow gas turbines. On the basis of the detailed geometry of blade and flow path, the fluid properties were investigated through the gas turbine. The results of the off-design performance of the compressor and turbine showed ±3% of deviation compared with the numerical data of JAEA. The reactor kinetic equations and the one-dimensional thermal–hydraulic modeling were successfully used to model the reactor and heat exchangers. The gas turbine characteristics are incorporated into the governing equations in the GAMMA code with a semi-implicit scheme. The direct implementation of the SANA code in the GAMMA code enables the precise and effective analysis of the dynamic behavior of PCS without requiring any tables or correlations to be extracted from the gas turbine characteristics maps. The GAMMA–SANA modeling provided more detailed understanding of the direct helium cycle with regard to the influence of the turbomachine performance, heat exchanger effectiveness, and the cooling flows. The steady-state simulation of full load operation showed good agreement with the GTHTR design in terms of the thermal–hydraulic cycle parameters. The GAMMA code has been equipped with control models for the purpose of describing the load transient of the entire HTGR system. Further applications of the dynamic models should be the comparison with the experimental data of HTGRs. With a better confidence in the obtained results, the models can be advantageous for the design and analysis of gas turbines and for design optimization of the heat and mass balance of plants.