Wavelet analysis of complex coolant flow behavior in fuel gaps of a pebble bed reactor

Coolant flow within the core of a Pebble Bed Modular Reactor (PBMR) shows highly complex characteristics which require comprehensive characterization of helium flow within the core. Consequently, in this study, velocity profiles within a near wall gap of a test section modeling the core of a PBMR is obtained using hot wire anemometry technique. Axial velocity profiles acquired at different flowrates for this gap present a velocity peak close to the outer wall of the core. This is in agreement with previous studies showing the bypass flow concept close to the wall of packed beds. Preliminary results of wavelet analysis performed on the velocity time histories at the peak point of the velocity profiles indicate some steady flow features at lower frequencies (= 0.1 Hz) for both cases under study while other unsteady flow patterns are observed at higher frequencies. Further analysis need to be performed to characterize the dominant frequencies and to comprehensively study the flow patterns occurring at these dominant frequencies. Moreover, further measurement and analysis in various gaps with different geometries would provide insight into the effect of the gap geometry on the flow behavior within the gaps and the bypass flow behavior.

Wavelet analysis of complex coolant flow behavior in fuel gaps of a pebble bed reactor Conference Paper