Application of cold crucible for melting of UO2/ZrO2 mixture

Using the cold crucible melting method, which has been found to be the best technique for the melt preparation of highly refractory materials, melting and discharge experiments for TiO2, ZrO2 and UO2/ZrO2 mixtures were conducted. The cold crucible, 15 cm in diameter and 20 cm in height, was used to get from 3 to 10 kg melts depending on the materials. Volatile gases generated during the melting period were well released through a hole of ∼2 cm in diameter and 10 cm in depth. The rubble crust layer with a gas vent hole, which is stably formed at the top of the melt, contributed to reduce the radiation loss from the melt surface. In reducing the thickness of the bottom crust, a partitioned plug is more effective than a solid plug, resulting in the easy achievement of the melt discharge. The most important factors for successful melting and discharge of refractory materials are the gas release hole and the plug shape. The developed melt discharge method was successfully applied to the fuel coolant interaction experiment using ZrO2 and UO2/ZrO2 mixtures.