There are thermal hydraulics issues of upper plenum of sodium cooled reactor ASTRID which can not 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 invetsigate temperature and velocity in this complex geometry. 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 fluorescent species within the flow. Typically, the tracer, an organic fluorescent dye such as Fluorescein or Rhodamine, 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 color LIF techniques are used to perform calibrations to study the fluorescence response of the dyes as function of main parameters: dye concentration, laser power, and temperature variation. Regarding PIV, the fluid is seeded with tracer particles then illuminated so that the particles are visible. The motion of the seeding particles is used to calculate velocity and direction of the flow being used. An experiment representative of the mixing flows in the MICAS mock up made up of two jets was designed to develop the LIF and PIV measurement process. The first jet is hot and the second cold, then optical methods for measuring simultaneously temperature by LIF and velocity by PIV is applied on the mock up. The interaction between the two jets at different temperatures and different configurations is studied regarding main dimensionless values such as Reynold's number, Richardson number and Froude number.