Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The deposition and resuspension behavior of carbonaceous dust in the primary circuit of a High Temperature Reactor (HTR) is a tremendous safety issue for the assessment of Design Basis Accidents. In this work the deposition of 18F labeled monodisperse aerosol particles in a pebble bed is recorded by means of Positron Emission Tomography (PET) in order to explore the particle behavior in this geometry. Our feasibility study gives first insights into the temporal and a fully 3D spatial distribution of the particle deposits in a pebble bed obtained by PET.
An air driven small scale test facility is used for the generation of a particle laden turbulent flow field through a model pebble bed. Its Reynolds numbers cover the range typically found in a HTR pebble bed. The results of total pressure drop measurements over the pebble bed with respect to Reynolds number show relatively good agreement to literature which assumes the correct fluid mechanic downscaling of the facility.
A condensational aerosol generator was charged with KF condensation nuclei labeled with 18F. The aerosols are made of DEHS and are injected far upstream from the pebble bed. Concentration measurements upstream and downstream of the pebble bed were performed by means of isokinetic sampling and a condensational particle counter. The results agree with typical deposition curves related to turbulent and inertia driven particle deposition.
A small portion of the initially applied activity was detected in the field of view of the scanner. The longitudinal, slice-wise activity distribution shows an exponential digression of deposited particles in downstream direction. In a deposition experiment in the inertia impact regime, PET image quality allows to conclude that the deposited particles are located in the vicinity of the upstream located stagnation points