Plasma melting technology uses electrical arc phenomena such as lightning to create hightemperature sparks of about 1,600 degrees or more to meet waste disposal requirements through treatment and reduction without distinguishing radioactive waste generated during nuclear power plant operation and dismantling according to physical characteristics. Decommissioning radioactive waste scabbed concrete occurs when polishing and cutting the contaminated structure surface to a certain depth. In this study, Scabbed concrete containing paint was confirmed for volume reduction and disposal safety using plasma treatment technology, and it is planned to be verified through continuous empirical tests.

Once decommissioning begins, it is expected that large amount of radioactive wastes will be produced in a short period of time. The expected amount of radioactive wastes from Kori unit 1 NPP are approximately 80,000 drums (base on 200 L). By minimizing the amount of radioactive wastes generated through decontamination and reduction, KHNP has set the final target for the amount of radioactive wastes to be delivered to the disposal site at approximately 14,500 drums. Here, plasma torch melting technology is an essential technology for radioactive wastes treatment during nuclear power plants decommissioning and operation, because of its large volume reduction effects and the diversity of disposable wastes. KEPCO KPS was able to secure experience in operating Plasma Torch Melter (PTM) by conducting a research service for ‘development of plasma torch melting system advancement technology’ at KHNP-CRI. This study will compare kilo and Mega-Watt class PTM, largely categorized into facility configurations, operating parameters, and waste treatment. Based on this study, it would be desirable to operate PTM with approximate capacity according to the frequency and amount of waste production, and suggest volume for a kilo and Mega-watt class plasma torch in the melting furnace respectively. This plays to its strengths for both a kilo and Mega-watt class PTM.

A disposal of radioactive wastes is one of the urgent issues in worldwide. Considering upcoming plans for decommissioning of nuclear power plants, this problem is unavoidable and should be discussed very thoughtfully before long. There are variety of methods to deal with radioactive wastes, including Incineration process, conventional gasification process and plasma gasification process and so on. Among them, plasma gasification process is in the limelight due to its ecofriendly features and very large volume reduction effects. So, lots of countries like Japan, Taiwan, Russia, Bulgaria are already utilizing commercial plasma melting facilities and researching their own characteristics & disposal abilities and so on. Within the scope of this paper, I would like to introduce other countries current status of plasma melting facilities, and reach the conclusion on the directions to go for realistic radioactive wastes treatment.

Plasma torch melting technology has been considered as a promising technology for treating or reducing the radioactive waste generated by nuclear power plants. In 2006, IAEA announced that the technology is able to treated regardless of the type of target wastes. Because of the advantage, many countries have been funding, researching and developing the treatment technology. In this study, oversea plasma torch melting facilities for radioactive wastes treatment are reviewed. Also, plasma torch melting facility developed by KHNP CRI is briefly introduced.

On March 11 2011, Fukushima Daiichi nuclear power plant site was attacked by a huge tsunami caused by Tohoku Pacific Ocean earthquake. Nuclear fuels of unit 1, 2, and 3 of Fukushima Daiichi nuclear power plant was melted down by the disaster. After the accident, Japan’s government has announced “Mid-and-Long-Term Roadmap towards the decommissioning of TEPCO’s Fukushima Daiichi Nuclear Power Station Units 1-4”. The topics of roadmap is made of measures to deal with contaminated water, removal of fuel rod assemblies from spent fuel pools, retrieval of fuel debris, measures to deal with waste materials, and other operations. To support the activity of the roadmap, various facilities about decommissioning have been established and operated on inside or outside of Fukushima Daiichi nuclear power plant site. Representatively, Collaborative Laboratories for Advanced Decommissioning Science which conducts R&D decommissioning, Naraha Remote Technology Development Center which develops remotes robots and VR (Virtual reality), Okuma Analysis and Research Center which performs radiochemical analyses for radioactive waste, and Fukushima Environmental Safety Center which conducts environmental dynamics and radiation monitoring.

Air conditioning facilities in nuclear power plants use pre-filters, HEPA filters, activated carbon filters, and bag filters to remove radionuclides and other harmful substances in the atmosphere. Spent filters generate more than 100 drums per year per a nuclear power plant and are stored in temporary radioactive waste storage. Plasma torch melting technology is a method that can dramatically reduce volume by burning and melting combustible, non-flammable, and mixed wastes using plasma jet heat sources of 1,600°C or higher and arc Joule heat using electric energy, which is clean energy. KHNP CRI & KPS are developing and improving waste treatment technology using MW-class plasma torch melting facilities to stably treat and reduce the volume of radioactive waste. This study aims to develop an operation process to reduce the volume of bag filter waste generated from the air conditioning system of nuclear power plants using plasma torch melting technology, and to stably treat and dispose of it. It is expected to secure stability and reduce treatment costs of regularly generated filter waste treatment, and contribute to the export of radioactive waste treatment technology by upgrading plasma torch melting technology in the future.

After the Fukushima accident, significant amount of radioactively contaminated waste has been generated with 50~250 m3/day and stored in tanks of the Fukushima Daiichi nuclear power plant site. The contaminated water is treated by various treatment facility such as KURION, SARRY, Reverse Osmosis, and ALPS to remove 62 radioactive nuclides except H-3. For the contaminated water treatment process, massive secondary wastes such as sludge, spent adsorbent, and so on as by-product are being generated by the facilities. In Japan, to treat the secondary wastes, melting technologies such as GeoMelt, In-can vitrification and Cold Crucible Induction Melting vitrification are considered as a candidate technologies. In this study, the technologies were reviewed, and the advantage and disadvantage of each technology were evaluated as the candidate technologies for treatment of the secondary wastes.

Hanford site has been operated since 1943 to produce the plutonium for nuclear weapons. Significant amount of radioactive wastes was generated by the nuclear weapons production process. The radioactive wastes are stored in 177 aged underground tanks. Due to the risk of leakage into the air and the Columbia River, the US DOE and EPA, and Washington State Department of Ecology organized the Tri-Party Agreement (TPA) to clean-up the Hanford site in 1989. The LAW (low-activity waste) vitrification facility named WTP (Waste Treatment Plant) is plan to vitrify about 212 million liters of radioactive waste. The US DOE announced that the world’s largest melter to vitrify the LAW was heated up on October 8, 2022.

A disposal of radioactive wastes is one of the critical issues in our society. Considering upcoming plans for dismantling of nuclear power plants, this problem is inevitable and should be discussed very carefully. There are variety of methods to handle with radioactive wastes, including Incineration, conventional gasification and plasma gasification. Among them, plasma gasification process is in the limelight due to its eco-friendly & stable operation, and large volume reduction effects. However, a fatal disadvantage is that it consumes more electric power than other methods, this leaves us a question of whether this process is indeed economical. Within the scope of this paper, I would like to introduce 4 cases which plasma facilities were evaluated economically in worldwide, and reach the conclusion on the economic feasibility of plasma process.

KHNP-CRI has developed small-capacity and Mega-Watt Class PTM (Plasma Torch Melter) for the purpose of reducing the volume of radioactive waste and immobilizing or solidifying radioactive materials. About 1 MW PTM is a treatment technology that operates a plasma torch and puts drumshaped waste into a melter and radioactive waste in the form of slag is discharged into a waste container. The small-capacity PTM is a treatment technology that operates a plasma torch and puts small amounts of radioactive waste by directly putting it into the melter through a waste input machine. Mega-Watt Class PTM was able to inject radioactive waste in drums, so it was disposed of without backloging. On the other hand, The small-capacity PTM put radioactive waste without a package, and the waste input was blocked. If even small-capacity PTM put radioactive waste in the form of small packages such as drums, it is expected that various types of radioactive waste can be processed for a long time. Packaging also reduces the risk of radioactive contamination.

Currently, KHNP-CRI has developed 100 kW plasma torch melting facility to reduce the amount of radioactive waste in nuclear power plant. Plasma torch melting technology uses electric arc phenomena like lightning to melt the target material at a high temperature of about 1,600°C. The technology is applicable to treatment for various types of waste such as combustible, non-combustible and mixed wastes. The volume reduction ratio by the technology is respectively expected to be about 1/60 of combustible wastes and about 1/5 for non-combustible wastes. It is important to discharge the melt without problems in the melting technology. In general, molten slag has properties such as high viscosity and quick solidification. Because of the properties, when discharging into slag container, the final product is accumulated like a mountain. To improve this problem, there is three suggestions; 1) rotation of the slag container, 2) vibration of the slag container, and 3) heating of the slag container.

By developing plasma torch melting technology in 1996, our company has developed the first generation 150 kW (’96~’02), the second generation 500 kW (’08~’12), and the third generation MW plasma torch melting facility (’14~’18), and completed facility upgrading (’20~’23). The MW plasma torch melting facility is equipped with CCTV to monitor waste input, melting, torch integrity, and melt discharge. The lens is installed inside a metal housing made of stainless steel to prevent damage caused by external impacts and high temperatures, and supplies nitrogen to prevent cooling and lens contamination. As a result of the demonstration test, as the temperature inside the melting furnace increased after starting the plasma torch, the resolution decreased along with noise in the CCTV, and facility monitoring was difficult due to high temperatures and foreign substances (fume). Based on the test results, CCTV was changed to a non-insertion type that was not directly exposed to high temperatures, and a filter (quartz) was additionally applied to monitor the melt smoothly. As a result of applying the newly manufactured CCTV to the demonstration test, smooth monitoring ability was confirmed even at normal operating temperature (above 1,500°C). Through this facility improvement, the operation convenience of the plasma torch melting facility has been secured, and it is expected that it will be able to operate stably during long-term continuous operation in the future.

Japan’s government has announced plan to release the contaminated water stored from the tanks of the Fukushima Daiichi nuclear power plant site into the sea in June. The contaminated water is treated by SARRY (Cesium removal facility) and ALPS (advanced liquid processing system) to remove 62 radionuclide containing Cesium, Strontium, Iodine, and so on using filtration, precipitation (or coprecipitation) and adsorption for other nuclides (except for H-3 and C-14). The total amount of the contaminated water stored at tanks is 1,328,508 m3 (as of March 23, 2023). Currently, three ALPS systems which are existing ALPS, improved ALPS, high performance ALPS have been operated to meet the regulatory standard for release to the sea. According to the release plan, they have announced that 30 nuclides and H-3 concentration of the contaminated water will be measured and assessed before/after the discharge of the contaminated water into the sea. Before the release, the contaminated water is re-treated by reverse osmosis membrane facility and additional ALPS. And then, the water will be diluted with seawater more than 100 times. The diluted water will then move through an undersea tunnel and be released about 1 kilometer off the coast.

Plasma melting technology is a high-temperature flame of about 1,600°C or higher generated using electrical arc phenomena such as lightning, and radioactive waste generated during the operation and dismantling of nuclear power plants is not classified according to physical characteristics. It is a technology that can meet waste disposal requirements through treatment and reduction. Plasma torch melting technology was used for volume reduction and stable treatment of HVAC filters generated from nuclear power plants HVAC (Heating Ventilation and Air Conditioning). filter was treated by placing 1 to 3 EA in a drum and injecting it into a plasma melting furnace at 1,500°C, and the facility was operated without abnormal stop. A total of 132.5 kg of filter was treated, and the high-temperature melt was normally discharged four times. It was confirmed that the plasma torch melting facility operates stably at 500 LPM of nitrogen and 370-450 A of current during filter treatment. Through this study, the possibility of plasma treatment of filters generated at nuclear power plants has been confirmed, and it is expected that stable disposal will be possible in the future.

Plasma torch melting has been considered as a promising treatment technology for radioactive waste generated by nuclear power plants. The IAEA reported in 2006, the plasma melting technology could be treated regardless of the type of radioactive wastes such as combustible, non-combustible and liquid. Also, the technology has the advantage of being an eco-friendly technology. It emits less harmful gases such as NOx, SOx, HCl and CO because it does not use fossil fuels. In KHNP CRI, the plasma torch melting system was developed as the new radioactive waste treatment technology. In this study, to evaluate the long-term integrity of the new facility, a demonstration test with concrete as a simulant was carried out for about 3 days. For the 3 days, the evaluation was conducted in view of abnormal shutdown, soundness of waste feeding device, electrode consumption, and so on.

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.

A plasma torch is a kind of equipment that utilizes an electric arc to dissociate a gas and transfer an electric energy to the gas to generate very high temperature flame. KHNP-CRI has been developed the Plasma Torch Melter (PTM) to reduce radioactive waste disposal volumes and drop the radiation level of wastes. As you guess, there is required condition for proper start-up operation like current, voltage, plasma gas flow, cooling water flow, temperature in melter and so on. Thus, the optimum start-up operation condition of plasma torch will be estimated experimentally in this paper.

Solid radioactive waste such as rubble, trimmed trees, contaminated soil, metal, concrete, used protective clothing, secondary waste, etc. are being generated due to the Fukushima nuclear power plant accident occurred on March 11, 2011. Solid radioactive waste inside of Fukushima NPP is estimated to be about 790,000 m3. The solid radioactive waste includes combustible rubble, trimmed trees, and used protective clothing, and is about 290,000 m3. These will be incinerated, reduced to about 20,000 m3 and stored in solid waste storage. The radioactive waste incinerator was completed in 2021. About 60,000 m3 of rubble containing metal and concrete with a surface dose rate of 1 mSv/h or higher will be stored without reduction treatment. Metal with a surface dose rate of 1 mSv/h or less are molten, and concrete undergoes a crushing process. About 60,000 m3 of contaminated soil (0.005 ~1 mSv/h) will be managed in solid waste storage without reduction treatment. The amount of secondary waste generated during the treatment of contaminated water is about 6,500 huge tanks, and additional research is being conducted on future treatment methods.

Recently, Japan’s government has announced Tokyo Electric Power Company’s plan to discharge contaminated water stored from the tanks of the Fukushima Daiichi nuclear power plant site into the sea. The contaminated water is treated by advanced liquid processing system (ALPS) to remove 62 radionuclide containing cesium, strontium, iodine and etc. using co-precipitation (or precipitation) and adsorption for other nuclides (except for tritium and carbon-14). The total amount of the contaminated water generated by ALPS facility is 1,311,736 m3 (as of August 18, 2022). The amount of contaminated water is estimated same as Tokyo dome volume. Under the sea discharge plan, the contaminated water will be diluted in seawater more than 100 times, and tritium concentration lowered 1/7 of the drinking water standard set by the World Health Organization (10,000 Bq/liters). The diluted water will then move through an undersea tunnel and be discharged about 1 kilometer off the coast.

Untreated waste is temporarily stored on the site of the nuclear power plant. In some nuclear power plants, saturation period of temporary storage waste is less than 10 years away. As untreated waste continues to be generated in nuclear power plants, it could also affect management of operations. Accordingly, CRI is developing the 3.5 generation plasma torch melting facility for waste treatment. The 3.5th generation plasma torch melting facility consists of melter, plasma torch, waste supply device, exhaust gas treatment facility, power supply, etc. Melter is composed of melting chamber for melting control and pyrolysis chamber for waste pretreatment, and dam-type discharge device is adopted to overflow the melt. Plasma torch is hollow type with reversed discharge, has a rating of megawatt class, and has two gas supply lines. It can be used in transfer mode, non-transfer mode and mixed mode. There are three types of device for waste supply. The first is a drum pusher for injecting 200 L drums, the second is a screw-type waste supply and hopper for injecting solid waste, and the third is a nozzle-type waste supply device for injecting liquid waste. Exhaust gas treatment facility was equipped with post combustion chamber, off-gas cooler, high-temperature filter, HEPA filter, reheater, scrubber, ID fan and etc. Power supply of plasma torch operation is designed with a capacity of 1.5 megawatt (Maximum) and consists of channels A and B. Transfer mode, non-transfer mode and mixing mode of plasma torch may be selected through the control of PLC. This paper introduces the composition and function of the 3.5th generation plasma torch melting facility of CRI. In order to solve the problems arising through the operation of the 3rd generation plasma torch melting facility, an optimization plan is applied.