Retrieving Fuel Elements by Pneumatic Suction in Pebble-Bed High Temperature Gas-Cooled Reactor

Spent fuel storage system of pebble-bed high temperature gas-cooled reactor needs to retrieve fuel elements and spent fuel elements from storage tank during fuel reloading condition and some other special status. This function is to be achieved by the negative pressure suction system. Research in depth is needed towards the negative pressure suction system design and experiment in order to reliably supply the system with enough suction capability and meanwhile prevent the fuel element from over-speed impact damage. A comprehensive experimental facility of negative pressure suction was built to investigate and verify the designed system. The facility mainly comprises a fuel canister, a suction tube, a tube feeder, a gas isolator, a Roots blower and pipelines. The negative pressure suction force was provided by the Roots blower and drove the fuel elements out of the canister through the tube. The Roots blower was driven by a frequency converter so that the suction flow rate could be adjusted as wanted. The dynamics model of spherical element in the tube was established. The pressure drop distribution of the negative pressure suction system was also calculated. Then the pressure drops and the sphere velocity were measured at different air flow rates. Based on the experimental results and calculation analysis, parameter requirements for the Roots pump were concluded. Therefore, fuel elements could be successfully retrieved without over-speed impact damage. These results provide useful experience for engineering design of negative pressure suction system in the spent fuel storage system.