Depending on the type of waste, DC plasma torch uses a transfer type operation for conductive waste and a non-transfer type operation for non-conductive waste. The transfer mode plasma torch can secure high throughput because the arc directly contacts the object and has high thermal efficiency. However, since the non-transfer mode does not have a higher thermal efficiency than the transfer mode, higher output is required to secure high throughput. A method of increasing the output of the plasma torch is increasing the current or extending the length of the plasma arc. However, the method of increasing the current affects the life of the electrode, and there is a limit to extending the arc length in the positive polarity plasma torch. Therefore, it is effective to design the plasma torch with reverse polarity to secure life and extend the arc length. In the reverse polarity plasma torch, the front electrode serves as the cathode, and the cathode point is not easy to control compared to the anode point, which may cause abnormal arcing and damage the plasma torch. This paper was conducted to investigate the conditions for securing the safety of these non-transferable reverse polarity plasma torch. The plasma torch is designed to have an output of 100 kW or less and to use the detachable nozzle to control the cathode point. The test showed that the shape of the nozzle prevented the cathode point moving outside of plasma torch and the excessive extension of the arc. Thanks to this, it was confirmed that plasma could be stably formed and abnormal arcing could also be prevented.

DC plasma torch is reported as a technology that can be treated regardless of waste types because it can select transfer or non-transfer operation modes depending on the electrical conductivity of waste. Thanks to this characteristic, countries that operate nuclear power plants such as Switzerland, Japan, and Taiwan have developed high-power DC plasma torch to dispose of radioactive waste. And also in korea, a plasma torch is being developed to dispose of radioactive waste. This study was conducted to investigate the characteristics of the reverse polarity plasma torch according to the conditions of interelectrodes. The inter-electrodes of plasma torch used in the study was designed to be 25, 37 mm in diameter and 180 to 400 mm in length. As a result of the test, it was confirmed that the smaller the diameter and the longer the length of the inter-electrode, the more advantageous it was to achieve a high output power. And it was confirmed that the power torch would be 500 kW when the diameter of the inter-electrode was 25 mm, the length was 400 mm, and the current was 500 A.