Simultaneous Measurements Of Temperature And Velocity By Optical Methods: Application To The Upper Plenum Of Sodium Cooled Nuclear Reactor Astrid

ASTRID, Advanced Sodium Technological Reactor for Industrial Demonstration is a pool type nuclear reactor which intends to be an industrial demonstration. There are thermal-hydraulic issues of the upper plenum of the sodium cooled reactor ASTRID which cannot be studied from past reactors feedback and numerical simulations since the calculation codes do not allow to model these problems with sufficient confidence. Thus in order to validate the numerical approaches and systems concept of ASTRID to fit the codes and simulations for validation and to better understand the complex thermal hydraulic phenomena in order to qualify the design options, we need to investigate temperature and velocity in this complex geometry. For these reasons, a prototype is needed to study the thermal hydraulic behavior of the ASTRID reactor. Sodium experiments are very complicated to perform since sodium is opaque and reacts violently with water, thus it was more useful to perform measurements on a water model since sodium and water have similar properties in terms of viscosity and density. The water model MICAS mock-up was constructed. One challenge is to implement non-intrusive optical techniques to simultaneously measure temperature and velocity on complex geometry featured by the MICAS Mock up.Laser induced fluorescence and Particle Image Velocimetry are optical methods used to measure temperature and velocity respectively. In all forms of LIF, a laser is used to excite a fluorescent species within the flow. Typically, the tracer is an organic fluorescent dye such as Fluorescein or Rhodamine. The dye absorbs a portion of the excitation energy and spontaneously re-emits a portion of the absorbed energy as fluorescence.In our experiments, single dye and two dye two color LIF techniques are used to perform calibrations to study the fluorescence response the dyes as function of main parameters: dye concentration, laser power and temperature variation. Regarding Particle Image Velocimetry, the fluid is seeded with tracer particles then illuminated so that particles are visible. The motion of the seeding particles is used to calculate speed and direction of the flow being studied.In parallel to this work, an experiment made up of two jets was designed to study the mixing flows in the MICAS mock up. The first jet is hot and the second cold such as the case in the MICAS mock-up and then optical methods for measuring temperature by LIF and velocity by Particle Image Velocimetry PIV simultaneously will be applied on the prototype. The prototype aims to study the interaction between two jets at different temperatures and these can be vertical or horizontal. In this study, three main dimensionless values will be studied, Reynolds number, Richardson number and Froude number.