FLOWBRAGG Project

In the framework of the FLOWBRAGG project (answer to OFFERR call for projects), a velocity sensor for water flow in narrow passages has been designed by the CEA (mechanical support) and Mons University, Belgium (fibre with Bragg gratings). The mechanical support of the sensor has been manufactured by French CYTech Ingénierie (Pégomas, France). This innovative sensor is projected for a use in experimental devices similar to JHR devices. The principle of the sensor relies on the measurement of temperature differences at several positions along the axis of the sensor that has to be aligned with the main direction of the flow. From these values, correlations between flow bulk velocity and temperature differences can be drawn. The sensor has been tested in a dedicated loop built at Mons University (Belgium). In parallel, CFD computations have been carried out by the CEA, using similar boundary conditions. Results from both methods are compared to assess the relevance of the sensor for bulk velocity measurements in channels where flow is fully developed. Qualitatively, both results show a good agreement, confirming the operating principle of the sensor. Still, a gap is observed between numerical and experimental values and would require further studies.

The objectives of the project are the followings:

• finishing the feasibility study, – carrying out the design of a first prototype of sensor,
• manufacturing the suitable fibre Bragg grating (FBG),
• manufacturing the mechanical support for FBG,
• assembling the sensor,
• adding the suitable interface for measurement acquisition,
• carrying out demonstration tests at room temperature and low pressure,
• identifying design improvements following demonstration tests.

Several tests where carried out:

• commissioning tests to confirm the correct operation of the loop and the relevant position of Bragg gratings,
• repeatability tests,
• hydrodynamic tests (sensitivity of Bragg measurement to hydraulic disturbance (found to be negligible),
• sensor calibration: 6 flow rates and 5 heating powers of the sensor to estimate temperature differences-velocity correlations,

• Conference proceedings in an ANIMMA typeconference (To be defined)

• CEA Cadarache (Nuclear, France)
• IAEC (Nuclear, Israel)