IMPROVEMENTS IN QUALITY OF AS-MANUFACTURED FUELS FOR HIGH-TEMPERATUREGAS-COOLED REACTORS

The mechanisms of coating failure of the fuel particles for the high-t emperature gas-cooled reactors during coating and compaction processes of the fuel fabrication were studied to determine a way to reduce the defective particle fraction of the as-manufactured fuels. Through the observation of the defective particles, it was found that the coating failure during the coating process was mainly caused by the strong me chanical shocks to the particles given by violent particle fluidizatio n in the coater and by unloading and loading of the particles. The coa ting failure during the compaction process tvas probably related to th e direct contact with neighboring particles in the fuel compacts. The coating process was improved by optimizing the mode of the particle fl uidization and by developing the process without unloading and loading of the particles at intermediate coating process. The compaction proc ess was improved by optimizing the combination of the pressing tempera ture and the pressing speed of the overcoated particles. Through these modifications of the fabrication process, the quality of the as-manuf actured fuel compacts was improved outstandingly.