Pebble bed nuclear reactor structure study: A comparison of the experimental and calculated void fraction distribution

The structure of the pebbles in the pebble bed nuclear reactors plays an important role in their performance as it affects the neutron streaming and the wall channeling of the coolant flow. In this study, the structure of a one foot diameter pebble bed reactor that was measured experimentally by gamma ray computed tomography (CT) in our laboratory in terms of void cross-sectional distribution and radial profiles has been used to evaluate the predictions of the void fractions of the reported empirical and analytical correlations. It can be seen that there is an agreement between the experimental results and the exponential expression for the void fraction with the use of the smaller spherical pebbles diameter (D/dp = 24) as compared to those of larger diameters.