Nuclear power plants in Korea stores approximately 3,800 drums of paraffin solidification products. Due to the lack of homogeneity, these solidification products are not allowed to be disposed of. There is therefore a need for the separation of paraffin from the solidification products. This work developed an equipment for a selective separation of paraffin from the solidification product using the vacuum evaporation and condensational recovery method in a closed system. The equipment mainly consists of a vacuum evaporator and a condensational deposition recovery chamber. Nonisothermal vacuum TGAs, kinetic analyses and kinetic predictions were conducted to set appropriate operation conditions. Its basic operability under the established conditions was first confirmed using pure paraffin solid. Simulated paraffin solidification product fixing dried boric acid waste including nonradioactive Co and Cs were then fabricated and tested for the capability of selective separation of paraffin from the simulated waste. Paraffin was selectively separated without entertainment of Co and Cs. It was confirmed that the developed equipment could separate and recover paraffin in the form of nonradioactive waste.

In domestic nuclear power plants, drums of concentrated radioactive waste solidified with paraffin that do not meet radioactive waste disposal standards are stored temporarily. In this paper, the design of a machine that separates these paraffin drums into paraffin and concentrated waste using heating vaporization and pressure difference is described. The separation process is as follows. First, the paraffin solid is indirectly heated by heating the outside of the drum. The paraffin solid is partially melted to increase the fluidity and is easily detached from the drum. The detached solid is transferred to the melting tank, and further heated in the melting tank. When the temperature is sufficiently high, paraffin is melted and becomes a mixture of liquid paraffin and concentrated waste homogeneously. The mixed solution is transferred to a paraffin recovery vessel and further heated. The vaporization point of paraffin is 370°C under atmospheric pressure, and becomes lower depending on the pressure decreasing in the vessel. The vaporization point of the paraffin is a relatively low value compared to the radioactive elements in the concentrated waste, and therefore only paraffin would be vaporized. A paraffin transfer pipe is installed on the upper part of the paraffin recovery vessel, and is connected to another tank called the paraffin capture vessel. The pressure of the paraffin capture vessel is reduced (i.e. vacuum condition), only gaseous paraffin is transferred to the paraffin capture vessel by the pressure difference. When the paraffin capture vessel is cooled below the vaporization point of the paraffin, the paraffin is liquefied or solidified, and only the paraffin is recovered. Based on the above process, the solidified paraffin could be separated into pure paraffin and concentrated waste. However, if a radioactive element with a lower vaporization point than paraffin exists in the concentrated waste, it may be mixed with paraffin and separated together. Therefore, it is necessary to measure the radioactivity or radiation dose rate for the separated paraffin, and to verify that it is sufficiently low. If necessary, additional separation process may be considered for removing radioisotopes from the paraffin.