Etude d’un cycle organique de Rankine couplé à un système passif innovant : application aux réacteurs nucléaires avancés

This work contributes to the design of passive backup systems for pressurized water reactors (PWRs) in use today.The reactor core residual power is the heat produced by the fission products left over after the nuclear reaction in the core has stopped. Passive safety condensers are one method for eliminating this power by using a large amount of water placed very high up, allowing residual heat to be removed naturally through convection. This uses a large amount of water that takes a long time to heat up to boiling temperature.The fundamental concept is to use a portion of the energy contained in this volume of boiling water as a heat source for a thermodynamic cycle through an immersed heat exchanger. The cycle power output will be used to supplement existing resources by providing electricity to various operating components on its own.The conversion of low and medium-temperature (< 150 °C) industrial or renewable (biomass, solar, geothermal) waste heat into electricity is a key challenge in energy efficiency. The organic Rankine cycle (ORC), which has been used on both laboratory and industrial scales for about ten years, is one potential method for capturing this heat.The nature of the hot source and the requirement for robustness and reliability in the system are two peculiarities related to the context of this work. In addition to the typical constraints imposed on this type of cycle, such as maximizing energy performance, respecting the environment, and minimizing space requirements.The purpose of the thesis was to investigate the behaviour of this complex system based on an ORC cycle using a methodology that combined modelling and experimentation, and thereby contribute to proving the validity of the selected approach. More specifically, an experimental test bench simulating the coupling between an ORC and a boiling water tank was dimensioned using a theoretical model. Thus, the satisfactory operation of the cycle and its adaptability to specific non-nominal conditions, such as an increase in the cold source temperature, the presence of liquid droplets at the turbine inlet, or the effects of a the working fluid charge in the ORC circuit, were both experimentally investigated. The ORC in the studied range have proven to be extremely reliable for a number of working fluids (Novec649TM, HFE7100) based on all of these off-design criteria. Architectural studies that were specifically focused on the coupling of ORC and water tank were also completed, with particular attention paid to the position of the evaporator immersed in the tank and the imposed power variation.All of these experimental findings aided the numerical simulations and theoretical models of the EES software. Finally, using these models allowed us to size the ORC on an industrial scale and make suggestions. These are specifically related to the ORC and condenser pool coupling architecture, as well as the multi-criteria analysis used to select the working fluid.