Normally, non-metallic wastes, such as sands, concrete and asbestos are regarded as electrically non-conductive materials. However, when the temperatures are increased up to the melting point, their electrical conductivities can be greatly improved, flowing arc current. Accordingly, these nonmetallic wastes can be efficiently treated by heating them up to the electrically conducting temperatures by using a non-transferred type plasma torch, and then, melting them completely with arc currents in transferred mode of plasma torch. For this purpose, we propose a convertible plasma torch consisting of three cylindrical electrodes (rear electrode, front electrode and exit nozzle). Compared with conventional plasma torch with two cylindrical electrodes (rear electrode and front electrode), the proposed plasma torch can provide more stable plasma jet in high powered and non-transferred mode due to the presence of exit nozzle, resulting in rapid heating of the non-conductive materials.

In KHNP CRI, the PTMs (plasma torch melting system) was developed as a treatment technology of a wide variety of radioactive wastes generated by nuclear power plants. The facility is made of melting zone, thermal decomposition zone, melt discharge zone, waste feeding device, MMI, and offgas treatment system. In this study, demonstration test was conducted using NaOH solution as liquid waste to evaluation the applicability of the PTM system. For demonstration test of NaOH solution treatment, the plasma melting zone is sufficiently pre-heated by the plasma torch for 5 hours. The temperature inside the plasma melting zone is about 1,600°C. The NaOH solution as simulant was put into the thermal decomposition zone by the spray feeding device with the throughput of maximum 30 liter/hour. During the test, the power of plasma torch is about 100 kW on the transferred mode. The 160 liters of liquid waste was treated for 500 minutes. After the demonstration test, the final product in the form of salt was remained in the melting zone, and the disposal of the final product are still under consideration.

In KHNP CRI, the 100 kW PTM (plasma torch melting) system was designed for the treatment and disposal technology of various radioactive wastes including the metal, concrete, liquid waste and insulator. The facility consists of melting chamber, thermal decomposition chamber, waste feeding system and off-gas treatment system. In this study, to evaluate the applicability of the PTM system, demonstration test was conducted using the radiation hazmat suit as combustible waste. The plasma melting chamber is pre-heated by 2nd combustion device and plasma torch for 5 hours. The temperature inside the plasma melting chamber is approximately 1,600°C. The combustible waste was put into the melting chamber by the pusher feeding device with the throughput of maximum 50 kg/hour. During the test, the power of plasma torch is 60–96 kW on the transferred mod. It was evaluated in terms of long-term integrity of PTM system on operation according to the waste throughput ratio.

Plasma melting technology has been considered as promising technology for treatment of radioactive wastes. According to the IAEA TECDOC-1527 report (2006), the technology has an advantage that it can treat regardless of waste types which is both combustible and non-combustible wastes. In particular, it is expected that a large amount of concrete, a representative non-combustible wastes, will be generated during the operation and dismantling of nuclear power plants. In order to treat the concrete waste in plasma torch melting system, various factors could be considered like the slag of electric conductivity, viscosity and melting temperature. Above all, as a critical factor, the viscosity of the melt is very important to easily discharge the melt. The viscosity of slag (SiO2-CaO-Al2O3 system) can be lowered by adding a basic oxide such as CaO, Na2O, MgO and MnO. The basic oxides are donors of oxygen ions. These oxides are called notwork breakers, because they destroy the network of SiO2 by reacting with it. In this study, the slag composition of the concrete waste was developed to apply the plasma torch melting. Also, demonstration test was performed with the developed slag composition and 100 kW plasma torch melting system.