Effect of cladding pre-oxidation on rod coolability during reactivity accident conditions

Sugiyama, Tomoyuki ; Fuketa, Toyoshi

This report discusses effect of cladding surface pre-oxidation on fuel rod coolability during reactivity initiated accident (RIA) conditions. NSRR irradiated fuel experiments had shown cladding surface temperature lower than fresh fuel experiments. One possible speculation for the temperature difference is that oxide layer at the cladding outer surface enhanced heat transfer. To verify the speculation, pulse irradiation tests were performed on fuel rods with three different surface conditions: without oxide layer, with 1m-thick and 10m-thick oxide layer. Transient records of the cladding surface temperature showed the critical heat flux and the minimum heat flux increased for the oxidized fuel rods. These effects depend on presence of the oxide layer, not on the thickness of the layer, because no difference existed between results from 1m and 10m rods.