Velocity measurements in the fuel gaps of a pebble bed reactor

The complex behavior of the helium coolant flow within the gaps of fuel elements in pebble bed reactors makes the velocity measurements in those regions highly important in the design and development of VHTR's. In this study, a Hot Wire Anemometry system is implemented to measure the coolant velocity at certain points between the spherical particles representing the fuel element in a pebble bed VHTR. The test facility is already constructed and the experimental study is at preliminary stages. The results of hot wire velocity measurements compares well with the results from previous studies confirming that the coolant flow passing through the fuel gaps has a complex structure. Further measurements and analyses are in progress in order to estimate the other velocity components and turbulence characteristics of the coolant flow such as turbulent intensities, Reynolds stresses, power spectra, etc. These statistics would improve the understanding of the gas flow behavior within the annular packed bed which is essential for having accurate predictions of the helium coolant flow inside the core of a pebble bed VHTR.