Numerical Investigation about Low Flow Characteristics of Purge Gas in Pebble Beds

Heat is also generated in the pebble beds, and the generated heat is removed through the wall surrounding the pebble beds. The purge gas is the helium gas with 0.1 % H2. The purge gas flows through the pebble beds and removes the tritium. The tritium is extracted from the purge gas through the several processes in a tritium extraction system (TES). The purge gas flow is limited to small flow rate due to the components specification of the TES. The size of the pebble is about 1 mm in diameter. The volume of the smallest pebble beds in the HCCR TBM is about 3,750,000 mm3. Thermal analysis is generally limited to simulating all pebbles independently. In the previous analysis, it is assumed that the pebble beds itself is simulated as a box, and the inside of the box is filled with the pebbles. This box is porous structure, and has relatively low thermal conductivity compared to the pebble. In this work, heat transfer characteristics of the pebble beds is studied when each pebble geometry and the purge gas flow are reflected. Thermal-hydraulic analysis was performed with a conventional CFD code, ANSYS-CFX. The thermal hydraulic analysis for the purge gas in the pebble beds is performed. The thickness with high temperature in the pebble beds is reduced when the simulation of the purgas flow is performed at same time.