Combination of Fuel-Cladding Chemical and Mechanical Interactions in Mixed Oxide Fuel Pins

Encapsulated mixed oxide fuel pins were irradiated in the Belgian reactor BR-2 under epithermal flux conditions. Of 12 pins, 5 failed. Heavy cladding corrosion and significant cladding deformation was observed in postirradiation examination. The failures are attributed to a combined action of fuel-cladding mechanical and chemical interactions, for which favorable conditions existed in these tests.