Assessment of performing experimental investigation on a pebble bed modular reactor (PBMR) as a static packed bed approximation

Moving bed reactors have a wide range of applications in the chemical, petrochemical, and alternative energy industries in a special situation where there is a need to either continuously recirculate or replace solid particles catalysts. They are also under consideration as one of the 4th generation nuclear reactors known as pebble bed modular reactor (PBMR). In this work a continuous cold flow pebble recirculation experimental set-up, mimicking the flow of pebbles in a PBMR, is designed, developed, and tested at Missouri S&T. A unique experimental work has been performed on assessment of the possibility of using pebble bed modular reactor (PBMR) as static packed bed approximation for the needed experimental investigation. For this purpose, a radioactive particle tracking (RPT) technique is implemented around the continuous pebble recirculation experimental set-up, to compare the packing characteristics of static and moving pebble beds. The photopeak counts during RPT calibration were collected by placing radioactive particle (tracer) at different positions in the test reactor under different operating conditions of moving and static conditions. The photopeak counts between moving and static conditions show that attenuation characteristics of the medium in between tracer and detectors are not changing significantly due to movement of pebbles. This confirms that PBMR could be well approximated by static packed beds for experimental investigation which simplify the needed experimentation to advance PBMR technology and commercialization. Obtained results are serving as a unique benchmark data for an evaluation of the contact force model that used in the discrete element method (DEM) based simulations.