A Review on Types of Induction Melter in Radioactive Treatment Waste Facilities

HyunMin Kim,JunKi Baik,SukWon Jung,GangWoo Ryu 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

The type of radioactive waste that may occur in the process of nuclear power plant dismantling can be classified into solid, liquid, gas, and mixed waste. The amount of these wastes must be defined in the Final Decommissioning Plan for approval of the licensing. Also, in the case of Metal radioactive waste, it is necessary to calculate the generation amount in order to treat radioactive waste at a Radioactive Waste Treatment Facility (RWTF). Since a large quantity of metal radioactive waste is generated during the decommissioning of a nuclear power plant, the application of a metal melter for reduction is considered. The metal waste is heated to a temperature above the melting point and separated into liquid and gas forms. Nuclides existing on the surface of metal waste vaporize in a melting furnace to become dust or collect in sludge. Nonvolatile nuclides such as Co, Fe and Mn remain in ingot, but other nuclides can be captured and reduced with dust and sludge. And the types of melting furnaces to be applied can be broadly classified into Atmospheric Induction Melter (AIM) and Vacuum Induction Melter (VIM). Therefore, this review intends to compare the two types of metal furnaces to be included in RWTF.

Design and Operations of a Melting Furnace System for Radioactive Metal Wastes

Hyejin Kim,Naon Chang,Heechul Eun 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

Various radioactive metal wastes are generated during operation and decommissioning of nuclear facilities. Radioactive metal wastes with complex geometries or volumetric contamination can be difficult to decontaminate and disposal costs may increase. To solve these problems, the radioactive metal wastes can be treated by melting method. In this study, we designed a melting furnace system of air induction melting type, which is widely utilized due to its advantages of good thermal efficiency, uniform heating and guaranteed safety for radioactive material. By utilizing the melting furnace system, volatile radionuclides existed in the base material can be captured in the form of gas or dust by the filter. The radionuclides whose chemical properties can easily form metal oxides present as slag. For this reason, the specific radioactivity of the base material can be reduced. Radionuclides that are difficult to transport to slag and dust are uniformly distributed in the base material. A dedicated power supply and a transformer were necessary to be included in the melting furnace system since the induction furnace uses high-frequency currents. In addition, a hood is placed on top of the furnace to capture fumes generated during melting, and additional hoods were installed around the furnace to remove airborne dust. In particular, a dust collection unit consisting of a cyclone and a HEPA filter were constructed to effectively collect dust containing radionuclides. During the melting process, the slag is removed and accumulated separately, and the ingot production system was designed to produce the ingot using molten metal. The furnace was constructed for tilting the molten metal by moving the furnace using hydraulic system. The water cooling system and cooling tower were prepared to cool off the equipment with high temperature during melting is cooled off. The above process was specified in the operating procedure developed for this melting furnace system, and the operator shall operate and inspect according to the prescribed procedures. The radioactivity concentration in the sample taken in the step of tilting shall be analyzed whether they meet clearance level for self-disposal determined and publicly announced by the Commission. We can conduct self-disposal for the product of melting furnace system confirmed by the Commission as having the radioactivity concentration by nuclide not exceeding the value determined by the Commission.

Considerations on Event Sequence and Consequences of Critical Hazards Generated From Operation of a Melting Facility for Metal Radioactive Waste

KwanSeong Jeong,KeunYoung Lee,SeungJoo Lim,HwanSeo Park,JaeYoung Pyo 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

The critical hazards generated from operation of a melting facility for metal radioactive waste are mainly assumed to be such as vapor explosion, ladle breakthrough and failure in the hot-cell or furnace chamber using remote equipment. In case of vapor explosion, material containing moisture and/or enclosed spaces may, due to rapid expansion of gases when heated, cause an explosion and/or violent boiling. The rapid expansion of gases may lead to ejection of molten radioactive metal from the furnace into the furnace hall. If there is a large amount of liquid the explosion may damage or destroy technical barriers such as facility walls. The consequences for the facility ranges from relatively mild to very severe depending on the force of the explosion as well as the type of waste being melted. Nonradiological consequences may be physical damage or destruction of equipment and facility barriers, such as walls. Due to the radiological consequences a longer operational shutdown would likely be required. Cleanup efforts would include cutting of solidified metal in a problematic radiological environment requiring use of remote technology before damage and repair requirements can be assessed. Even though there is a risk for direct physical harm to operators for example in the control room and hot-cell, this analysis focuses mainly on the radiological impact. The extent to which remote equipment could be used in the decontamination effort will largely determine the health consequences to the workers. It is reasonable to assume that there will be a need for workers to participate manually in the effort. Due to the potentially large dose rates and the physical environment, it is possible that the maximum allowable dose burden to a worker will be reached. No major consequence for the environment is expected as most of the radioactivity is bound to the material. In case of ladle breakthrough, a ladle breakthrough involves loss of containment of the melt due to damage of the ladle. This may be caused e.g. by increased wear due to overheating in the melt, or from physical factors such as mechanical stress and impact from the waste. A ladle breakthrough may lead to spread of molten metal in the furnace hall. Molten metal coming into contact with the surrounding cooling equipment may cause a steam explosion. The consequences of a ladle breakthrough will depend on the event sequence. The most severe is when the molten metal comes into contact with the cooling system causing a vapor explosion. The basic consequences are assumed to be similar to those of the vapor explosion above. While the ejection of molten metal is likely more local in the ladle breakthrough scenario, the consequences are judged to be similar. In case of failure in the hot-cell or furnace chamber using remote equipment, the loss of electric supply or technical failure in the furnace causes loss of power supply. If not remedied quickly, this could lead to that the melt solidifies. A melt that is solidified due to cooling after loss of power cannot be removed nor re-melted. This may occur especially fast if there is not melted material in the furnace. An unscheduled replacement of the refractory in the furnace would be required. It could be unknown to what degree remote equipment can be used to cut a solidified melt. It is therefore assumed that personnel may need to be employed. This event could not have any impact on environment

Analysis of Size Distribution for Radioactive Aerosols Generated When Decommissioning Nuclear Power Plants

Ji Ung Kim,Seong Jun Kim,Jin Ho Son,Hwa Pyoung Kim,Chang Ju Song,Wo Suk Choi,Tae Young Kong 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

Metal waste generated during the dismantling of a nuclear power plant can be contaminated with radionuclides. In general, the internal structure is very complex. Thus, metal waste requires various cutting processes. When metal waste is cut, aerosols are generated. Aerosols are generally various particles of very small size suspended in the working area and remain for a considerable period. This may cause internal exposure of workers due to inhalation of radioactive aerosols generated when cutting radioactive metal waste. This study investigated various cutting processes and the size distribution of aerosols generated during the cutting process. The cutting process is normally classified into thermal cutting, mechanical cutting, and laser cutting. Thermal cutting includes plasma, flame, and oxygen cutting. Mechanical cutting includes mechanical saws, cutters, nibblers, and abrasive water jets. Stainless steel, carbon steel, aluminum, and copper are commonly used as cutting materials in nuclear power plants. The size of the aerosol generated from cutting showed a very diverse distribution depending on the cutting methods and cutting materials. In general, aerosol size is distributed within 0.1-1 μm. This size distribution is different from the 5 μm aerosol size suggested by the ICRP Publication 66 Lung model. These results show that it is necessary to conduct further studies on the size of aerosols generated when decommissioning nuclear power plants.

Self-disposal of Metal Radioactive Waste

Kyeong Min Park,Si Hyung Kim,Jong Hun Kim,Yun Jeong Hong,Seong Jae Cheon,Sunghwan Kim,Yong Jin Jeong 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2

The fuel fabrication facility has been built and is being operated by KAERI since licensing research reactor fuel fabrication in 2004. After almost 20 years of operation, outdated equipment for fabrication or inspection has been replaced by automated, digitalized ones to assure a higher quality of nuclear fuels. However, the generation of a large amount of radioactive waste is another concern for the replacement in terms of its volume and various types of it that should be categorized before disposal. The regulatory body, NSSC (Nuclear Safety and Security Commission) released a notice related to the classification of radioactive wastes, and most accessory equipment can be classified into the clearance levels, called self-disposal waste. In this study, the practice of self-disposal of metal radioactive waste is carried out to reduce its volume and downgrade its radioactivity. For metal radioactive waste, which is expected to occupy the most amount, analysis status and legal limitations were performed as follows: First, the disposal plan was established after an investigation of the use history for equipment. Second, those were classified by types of materials, and their surface radio-contamination was measured for checking self-disposable or not. After collecting data, the plan for the self-disposal was written and submitted to the Korea Institute of Nuclear Safety (KINS) for approval.

개선된 중성염 전해공정을 이용한 모의 방사성금속폐기물의 제염

이지훈,육완이,양호연,하종현 대한방사선 방어학회 2002 방사선방어학회지 Vol.27 No.2

원자력발전소에서 주로 발생되는 금속폐기물인 탄소강을 중성염전해질인 1.7M의 황산나트륨(Na₂SO₄)과 질산나트륨(NaNO₃)을 이용하여 기존전해제염과 개선된 전해제염공정의 비교실험을 수행하였다. 양극은 인코넬, 음극은 티타늄으로 하여 상온에서 1시간동안 반응시켜 금속폐기물 모재의 weight loss, 두께변화, 전해질 내 침전물농도, SEM을 이용하여 제염전후의 금속폐기물 표면의 형상을 분석하였다. 실험결과 개선된 전해제염 적용시 전해질 종류별 전류밀도 변화에 따른 실험에서는 전류밀도가 0.1∼0.6A/cm²으로 증가함에 따라 1.7M의 황산나트륨 적용시 금속폐기물 모재의 두께변화는 0.48±0.005∼67.7±0.02um, 1.7M의 질산나트륨 적용시에는 0.06±0.005∼17.7±0.05로 나타나 같은 전류밀도에서 황산나트륨 적용시 금속폐기물 모재의 표면 제염효율이 더욱 높은 양상을 보였다. 또한 전류밀도 0.3 A/cm² 및 1.7M의 황산나트륨의 조건에서 개선된 전해제염 적용 시 9.8±0.01um의 금속폐기물 두께변화를 보여 기존전해제염 적용시인 3.7±0.03um의 금속폐기물 두께변화보다 2배 이상의 표면 제염효과를 보였다. Conventional and modified electrolytic decontamination experiment were performed in the 1.7 M solution of sodium sulfate and sodium nitrate for decontamination of carbon steel as the simulated metal wastes which have been produced in large amounts from nuclear power plants. Anode and cathode were used as inconel and titanium respectively. The reaction time and temperature were 1 hr and 25℃. The analyses were performed of the characteristics such as weight loss and thickness change of metal waste, suspended solid in electrolyte and SEM observation. In modified electrolyte decontamination system with increased current density ranged from 0.1 to 0.6 A/cm², the metal waste showed thickness changes of 0.48±0.005 to 67.7±0.02um in 1.7 M sodium sulfate and those of 0.06±0.005 to 17.7±0.05um in sodium nitrate. Metal waste in modified electrolyte decontamination system showed the thickness change of 9.8±0.01um while it reacted up to 3.7±0.03um in conventional system with 0.3 A/cm² of current density and 1.7 M sodium sulfate. Decontamination efficiencies of modified electrolytic process are much higher than that of conventional electrolytic process when both are applied to metal waste.

이동형 방사화학 분석시설에서의 해체 금속폐기물 전처리작업자 피폭 평가 연구

이상헌,이민호,안홍주,송종순 (사)한국방사선산업학회 2021 방사선산업학회지 Vol.15 No.1

Radioactive waste generated by nuclear facilities has various shapes and levels, soaccurate source terms must be derived. In the case of nuclear power plants, metal and concretewastes account for a large proportion of the decommissioning waste. In addition, since the wastesubject to clearance accounts for more than 90%, rapid radiochemical analysis is required. This study to preliminarily evaluate the external exposure of pretreatment workers in a mobileradiochemical analysis facility to analyze wastes generated when decommissioning a nuclearpower plant. In pre-treatment work, the point source method and point kernel method were usedto evaluate external exposure. Preliminary evaluation results were derived by using the inputfactors (source term, sample size, time, etc.) expected to be applied at the mobile radiochemicalanalysis facility.

방사성 금속폐기물의 방사능 오염도 측정 및 오염 여부에 따른 자동 분류시스템 개념설계 및 개발

권순범,김보길,염정민,이경모,이홍연,한상준 (사)한국방사선산업학회 2023 방사선산업학회지 Vol.17 No.1

Waste generated during the dismantling of nuclear power plants is not only diverse in typessuch as metal, concrete, soil, but also in a large amount, requiring systematic and efficient management. It is very important to quickly and accurately measure radioactive contamination of wastes generatedsimultaneously at the decommissioning site, classify them by level, and make decisions so that theycan be disposed of in accordance with related laws and regulations. In this paper, for the technical andeconomic aspects of recycling of radioactive metal waste generated during the dismantling of nuclearpower plants, we propose a management system that can measure the radioactive contamination byshape of metal waste at the decommissioning site and automatically classify it according to the presenceor absence of contamination. Accordingly, a system for collecting information on metal samples such asweight measurement and shape acquisition of metal waste, measurement of radioactive contaminationand identification of nuclides, and an automatic classification system according to radioactivitymeasurement results were described.

원자력시설 해체 금속폐기물 용융제염 현황과 전망

민병연,이기원,윤경수,문제권 한국폐기물자원순환학회 2012 한국폐기물자원순환학회지 Vol.29 No.7

This paper describes the domestic and international status for melt decontamination, which has been known as the most effective technology for the volume reduction and recycling of the metal wastes generated from nuclear facilities. The recycle or self disposal of metallic wastes can be considered as one of the waste management options under the circumstances of the capacity limitation of a waste disposal in Korea. The limited recycle or self disposal of the metal wastes through an melt decontamination have the merit from the positive view point of the increase in resource recyclability as well as the decrease in the amount of wastes to be disposed resulting the reduction of disposal cost and the enhancement of disposal safety. Among the scenarios for recycle and reuse of the radioactive metallic wastes, the most feasible and reasonable one is limited reuse option, in which the ingot can be recycled as the products such as the waste drums and ISO containers. Prior to recycle and reuse in the nuclear sector, however, the regulatory criteria for the recycle and reuse of metallic wastes should be established in parallel with the development of the recycling technology.

Characterization of Fine and Ultrafine Particles Generated During the Dismantling of a Mock-up Reactor Pressure Vessel

Wonseok Yang,Minho Lee,Samuel Park,Nakkyu Chae,HaeWoong Kim,Kwangsoo Park,Sungyeol Choi 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

Cutting reactor pressure vessels (RPV) into acceptable sizes for waste disposal is a key process in dismantling nuclear power plants. In the case of Kori-1, a remote oxyfuel cutting method has been developed by Doosan Heavy Industry & Construction to dismantle RPVs. Cutting radioactive material, such as RPV, generates a large number of fine and ultrafine particles incorporating radioactive isotopes. To minimize radiological exposure of dismantling workers and workplace surface contamination, understanding the characteristics of radioactive aerosols from the cutting process is crucial. However, there is a paucity of knowledge of the by-products of the cutting process. To overcome the limitations, a mock-up RPV cutting experiment was designed and established to investigate the characteristics of fine and ultrafine particles from the remote cutting process of the RPV at the Nuclear Decommissioning Center of Doosan Heavy Industry & Construction. The aerosol measurement system was composed of a cutting system, purification system, sampling system, and measurement device. The cutting system has a shielding tent and oxyfuel cutting torch and remote cutting robot arm. It was designed to prevent fine particle leakage. The shielding tent acts as a cutting chamber and is connected to the purification system. The purification system operates a pressure difference by generating an airflow which delivers aerosols from the cutting system to the purification system. The sampling system was installed at the center of the pipe which connects the shielding tent and purification system and was carefully designed to achieve isokinetic sampling for unbiased sampling. Sampled aerosols were delivered to the measurement device. A high-resolution electrical low-pressure impactor (HR-ELPI+, Dekati) is used to measure the size distribution of inhalable aerosols (Aerodynamic diameter: 6 nm to 10 μm) and to collect size classified aerosols. In this work, the mock-up reactor vessel was cut 3 times to measure the number distribution of fine and ultrafine particles and mass distribution of iron, chromium, nickel, and manganese. The number distribution of aerosols showed the bi-modal distribution; two peaks were positioned at 0.01?0.02 μm and 0.04–0.07 μm respectively. The mass distribution of metal elements showed bi-modal and trimodal distribution. Such results could be criteria for filter selection to be used in the filtration system for the cutting process and fundamental data for internal dose assessment for accidents. Future work includes the investigations relationships between the characteristics of the generated aerosols and physicochemical properties of metal elements.