Coupling of Molten Salt and Supercritical CO₂ Circuits: Design and Operational Experience

Compared to conventional technology, power cycles that use supercritical carbon dioxide (sCO2) as working fluid promise more effective energy conversion, very low dimension, and high flexibility, especially at high temperatures. These abilities are very suitable for use with advanced small modular reactors (SMRs). The concept of an SMR based on a fluoride salt (FLiBe) coolant and a sCO2-based conversion cycle, called ‘Energy Well’, is being developed by Centrum výzkumu Řež (CVR). During the research and development of the Energy Well nuclear reactor and long-term activities of CVR in the field of sCO2 technologies, a loop-type experimental facility working with FLiBe was developed, assembled, and operated. The facility was coupled with another unique infrastructure, the sCO2 loop, to support the development of a potential interface between the FLiBe coolant and an innovative conversion cycle fluid (sCO2). This facility intends to test the key components and operational procedures important in the application of similar technologies on a larger scale. The key components of the FLiBe loop are the main circulation pump, the heat exchanger (FLiBe/sCO2) and the electrical heater, which represents the core of a molten salt reactor. All components were developed and assembled by CVR. Some aspects of the design of these components were validated using CFD tools. A description of the first operational experience and experimental data are provided in this paper. The resulting outlet temperatures, heat flux and FLiBe mass flow rate were compared with experimental measurements and the overall heat transfer coefficient was estimated. As part of the experimental campaign, the circulation pump for FLiBe was first tested separately. After this successful test, the experimental FLiBe circuit was connected to the existing sCO2 loop, which is operated by CVR, via the heat exchanger. During the experimental campaign, data were obtained from the operations of both coupled devices, including from the commissioning procedure of the FLiBe circuit and the controlling of the two devices simultaneously. Experimental data were processed and evaluated. Unfortunately, large uncertainties were found in the FLiBe temperature measurements and, consequently, the resulting mass flow rates.