Cold crucible induction melter (CCIM) technology has been widely used in melting of non-metallic refractory materials with a high melting point and a requirement of high purity. This paper discusses the application of the CCIM technology in melting of reactor corium (simulated as zirconium oxide in this experiment).
In this experiment, the power supply is set at constant power control mode, with a design frequency of ∼100 kHz and a total output power of ∼ 400 kW. The cold crucible consists of copper tubes and a stainless bottom plate which has a dimension of 220 mm in diameter and 420 mm in height. The crucible is charged with zirconium oxide (ZrO2) powder and surrounded by a set of water-cooling induction coils which is designed shorter than the crucible in order to reduce energy loss in the water-cooling bottom plate. The top of the crucible and the coils are at the same height. A Zirconium ring is used to initiate heating process. ∼ kg ZrO2 powder is used for each experiment. Electrical variables of the induction melter and temperature of the melt are detected and recorded in the entire heating process.
For the result, almost 3/4 of the ZrO2 powder is melt and a thin crust (∼ 2–3 mm) is generated between the melt and the crucible. To be specific, the ZrO2 powder above the bottom of the induction coils is melt, but others are not. In the melting process, the maximum surface temperature of the melt has reached 2230°C. Furthermore, for better understanding of the relationship between the melting process and the changing process of the electrical variables, an equivalent circuit of the heating system is established and analyzed. It can be concluded that some electrical variables such as the quality factor (Q) of the induction coils and the practical frequency can reflect melting status. The conclusion is confirmed by the records transmitted by sensors in the melting process. By comparison between the recorded data and the melting status, it is clear that the Q value can be accurately used in indicating the melting status due to its obvious change in the entire melting process. As the melting pool becoming larger, the Q value tends to be smaller. In contrast, the practical frequency becomes higher as the melt becoming larger. Furthermore, both of them are not influenced by the output power. In addition, the output current and the output voltage also can be used to describe the melting status. In specific, a larger melting pool corresponds to a lower output current and a higher output voltage.