Study of the electromagnetic pumping systems of molten metals and molten salts

The actual concerns with respect to safe operation of existing nuclear plants and to designing special architectures envisaged for the fourth generation of nuclear reactors, corroborated with the increasing interest for efficiency and reliability of any equipment belonging to an energetic system, make that more and more research endeavors to be devoted to the study of various parts of these systems for a better understanding and optimization based on modern techniques of computer aided design. Among the types proposed for the fourth generation of nuclear reactors belong those that have as cooling agent molten salts, respectively liquid sodium. Many reactors of previous generations use mechanical pumps of special design for driving the coolants. Molten salts and liquid sodium, thanks to their physical properties, have the potential to be driven using electromagnetic pumps. Although the technology of electromagnetic pumping of electro-conductive fluids was developed since the first half of the last century, currently it undergoes a revival due to the reconsideration of its multiple technological and security advantages. This work is both an intimate study of the phenomena that occur as a result of the electro-conductive fluids flow in the electromagnetic field of an electromagnetic pump - magnetohydrodynamic interaction - and a report on the capabilities and advantages of modern computational tools to facilitate the design and optimization of electromagnetic pumps. To achieve the principal goal of deeper understanding of the interdependent phenomena specific to electromagnetic pumps operation, two auxiliary objectives were considered. The first one is related to the full exploitation of electromagnetic finite element models in order to retrieve as much information as possible about electromagnetic pumps behavior in a simplifying hypothesis that does not take into account the fluid dynamics. The second auxiliary objective is to build numerical models that couple the electromagnetism and the fluid dynamics, namely the two interdependent physics that govern the magnetohydrodynamic flow through channels of electromagnetic pumps. In the section dealing with the study of electromagnetic pumping of molten salts, the thesis highlights specific problems related to the generation of electromagnetic forces in fluids with low electrical conductivity and provides results with respect to applications where electromagnetic pumping of molten salts can be effective. With the electromagnetic numerical models were obtained important data about the influence of the number of electromagnetic poles and supply frequency on the Pressure/Velocity characteristic of annular linear induction pumps. Were analyzed the shielding effect generated by the metallic walls - with negative repercussions on pumps performances, braking effects exerted at pump inlet and pump outlet and the connection between the overload capacity and Pressure/Velocity characteristic of induction pumps. A special portion was devoted to the analysis of the time and space dependence of the electromagnetic force and to the study of the non-uniformities of electromagnetic quantities in azimuth direction of annular linear induction pumps. In the chapter devoted to the magnetohydrodynamic interaction through coupled models, the thesis proposes two models that couple the electromagnetism and the fluid flow, one realized using multi-physic software and the second by coupling two different softwares. There are presented the advantages of the coupled models with respect to the results accuracy in comparison with electromagnetic models. It is presented the evolution of velocity, force and current densities profiles under the influence of the electromagnetic field and of different sodium mean velocities. It is shown that a good approximation of the electromagnetic pump efficiency requires the use of coupled models that take into account the hydrodynamic losses and the effects of turbulence. The contributions of the thesis are completed with significant observations related to the study methods and software tools used along the study process. (author)