Experimental investigation on the heat transfer between condensing steam and supercritical CO2 in compact heat exchangers

Abstract

In the frame of the sCO2-HeRo project, a self-launching, self-propelling and self-sustaining decay heat removal system with supercritical CO2 as working fluid is developed. This system can be attached to existing nuclear power plants and should reliably transfer the decay heat to an ultimate heat sink, in case of a combined station black-out and loss-of-the-ultimate-heat-sink accident scenario. Thereby the nuclear core is sufficiently cooled, which leads to safe conditions. To demonstrate the feasibility of such a system and to gain experimental experience, a small-scale sCO2-HeRo system is designed, built and installed into the pressurized water reactor glass model at GfS, Essen. The obtained experimental results are used to validate correlations and models for pressure drop and heat transfer, which are implemented in the German thermal-hydraulic code ATHLET. In consideration of the validated models and correlations, new ATHLET simulations of the sCO2-HeRo system attached to a NPP are performed and the results are analyzed. After the motivation, the state of the art is summarized, including an outline of the simulation work with the ATHLET code, a summary of sCO2 test facilities and a description of currently performed experimental heat transfer investigations in heat exchangers with sCO2 as working fluid. The main objectives of the work are derived from there. The chapter "sCO2-HeRo" starts with a description of the pressurized water reactor glass model. Afterwards, the basic sCO2-HeRo system is explained before a detailed description of the sCO2-HeRo system for the PWR glass model and for the reactor application is presented. Afterwards, cycle calculations are performed for both systems to determine the design point parameters in consideration of boundary conditions, restrictions and assumptions with respect to maximum generator excess electricity. In the following chapter, the test facility for the investigations on the heat transfer capability between condensing steam and sCO2 is described. It consists of the sCO2 SCARLETT loop, a high-pressure steam cycle and a low-pressure steam cycle.The installed measurement devices, measurement uncertainties and calculated error propagations are explained as well. After a fundamental classification of heat exchangers, the 7 heat exchanger test configurations are summarized before the diffusion bonding technique, the used plate material, the mechanical design, the plate design and the manufacturing steps of the heat exchanger test plates are described. In the chapter "Results", the measurement points are described and an overview of the performed measurement configurations is given before a summary of all measurement results is presented. After that, experimental results of the sCO2 pressure drop for unheated flows as well as for heated flows are depicted and explained, followed by the analysis of the experimental heat transfer results. The chapter "CHX for the PWR glass model" starts with a summary of the boundary conditions and measurement results with regard to the design of the heat exchanger for the sCO2-HeRo system of the glass model. Subsequently, the plate design is presented and manufacturing steps of the heat exchanger are described by means of pictures. The chapter "ATHLET simulations" starts with an introduction before the development of performance maps, models and the validation of correlations based on experimental results as well as CFD simulation results are described. In the following, these models and performance maps are transferred to a sCO2-HeRo system that can be attached to a nuclear power plant. Finally, further cycle simulations are carried out and the simulation results are analyzed.