• 한국기계가공학회지
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• 제21권1호
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• pp.22-27
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• 2022

In accordance with the growing trend of decommissioning nuclear facilities, research on the cutting process is actively proceeding worldwide. In general, a thermal cutting process, such as plasma cutting is applied to decommissioning a nuclear reactor pressure vessel (RPV). Plasma cutting has the advantage of removing the radioactive materials and being able to cut thick materials. However, when operating under water, the molten metal remains in the cut plane and re-solidifies. Hence, cutting is not entirely accomplished. For these environmental reasons, it is difficult to cut thick metal. The contact arc metal cutting (CAMC) process can be used to cut thick metal under water. CAMC is a process that cuts metal using a plate-shaped electrode based on a high-current arc plasma heat source. During the cutting process, high-pressure water is sprayed from the electrode to remove the molten metal, known as rinsing. As the CAMC is conducted without using a shielding gas, such as Argon, the electrode is consumed during the process. In this study, CAMC is introduced as a method for dismantling nuclear vessels and the relationship between the metal removal and electrode consumption is investigated according to the cutting conditions.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2356-2365
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• 2023

Characterization, dismantling and pre-disposal management of irradiated graphite (i-graphite) have an important role in safe decommissioning of several nuclear facilities which used this material as moderator and reflector. In addition to common radiation protection issues, easily volatizing long-lived radionuclides and stored Wigner energy could be released during imprudent retrieval and processing of i-graphite. With this regard, among all cutting technologies, abrasive waterjet (AWJ) can successfully achieve all of the thermo-mechanical and radiation protection objectives. In this work, factorial experiments were designed and systematically conducted to characterize the AWJ processing parameters and the machining capability. Moreover, the limitation of dust production and secondary waste generation has been addressed since they are important aspects for radiation protection and radioactive waste management. The promising results obtained on non-irradiated nuclear graphite blocks demonstrate the applicability of AWJ as a valid technology for optimizing the retrieval, storage, and disposal of such radioactive waste. These activities would benefit from the points of view of safety, management, and costs.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.156-157
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• 2021

Since concrete is contaminated or radioactive during operation of nuclear power plants, it is the most important radioactive waste generated during the dismantling of a nuclear power plant. The amount of waste is different depending on the pollution state of each facility and the applied technology is different, so there is a big difference. We aim to reduce the amount of waste and increase the value of recyclability through technology to remove radionuclides attached to the surface. For this purpose, laser scabbling, which exfoliates the surface of concrete by irradiating a laser, and a facility system for controlling dust and dust are used in parallel. The purpose of this study is to evaluate the efficiency of laser scabbling by manufacturing simulated concrete for nuclear facilities, and to review the optimal mixing design conditions for nuclear facility structures.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4181-4190
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• 2023

Nuclear power plants are subjected to various processes during decommissioning, including cutting, decontamination, disposal, and treatment. The cutting of massive bio-shields is a significant step in the decommissioning process. Cutting is performed near the target structure, and during this process, workers are exposed to potential radioactive elements. However, studies considering worker exposure management during such cutting operations are limited. Furthermore, dismantling a nuclear power plant under certain circumstances may result in the unnecessary radiation exposure of workers and an increase in secondary waste generation. In this study, a cutting scenario was formulated considering the bio-shield as a representative structure. The specifications of a standard South Korean radioactive waste disposal drum were used as the basic conditions. Additionally, we explored the hot-to-cold and cold-to-hot methods, with and without the application of polishing during decontamination. For evaluating various scenarios, different cutting time points up to 30 years after permanent shutdown were considered, and cutting speeds of 1-10nullm²/h were applied to account for the variability and uncertainty attributable to the design output and specifications. The obtained results provide fundamental guidelines for establishing cutting methods suitable for large structures.

• 한국압력기기공학회 논문집
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• 제16권2호
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• pp.18-24
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• 2020

When a damage occurs in the nuclear fuel burning in the reactor, fission products that should be in the nuclear fuel rod are released into the reactor coolant. In this case, sipping test, a series of non-destructive inspection methods, are used to find leakage in nuclear fuel assemblies during the power plant overhaul period. In addition, the sipping test is also used to check the integrity of the spent fuel for moving to an intermediate dry storage, which is carried out as the first step of nuclear decommissioning, . In this paper, the principle and characteristics of the sipping test are described. The structure of the sipping inspection equipment is largely divided into a suction device that collects fissile material emitted from a damaged assembly and an analysis device that analyzes their nuclides. In order to make good use of the sipping technology, the radioactive level behavior of the primary system coolant and major damage mechanisms in the event of nuclear fuel damage are also introduced. This will be a reference for selecting an appropriate sipping method when dismantling a nuclear power plant in the future.

• 방사성폐기물학회지
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• 제18권1호
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• pp.103-111
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• 2020

콘크리트 구조물 절단에 사용되고 있는 다이아몬드 와이어 쏘가 장착된 당김형 절단 장치의 단점을 개선하여 밀기형 절단장치를 개발하였다. 개발된 밀기형 절단장치에는 먼지 집진 커버가 부착되며 마찰열을 냉각하기 위한 건식이나 습식방법을 선택할 수 있다. 개발된 절단장치의 동작특성과 집진 먼지의 누설률 측정을 실험하였다. 시험결과 원활한 동작특성을 보였으며, 먼지의 누설률은 1.7%인 것으로 나타났다. 개발된 절단장비를 사용하여 생물학적 차폐 콘크리트 절단 시 작업자의 내부 피폭선량을 평가하였다. 보수적 평가를 위해 노심 중심부분을 절단하는 경우를 가정하였다. 비방사능이 99.5 Bq·g^-1인 누설 먼지로 인해 반면마스크를 착용한 작업자의 예탁유효선량은 0.25 mSv로 평가되었다. 개발된 밀기형 절단장비 사용 시 미량의 먼지 누설률로 인해 작업자의 방사선 피폭이 저감되며, 사용의 편리성으로 세부 절단 계획을 수립할 수 있어 방사성 콘크리트 폐기물 감량에도 기여할 수 있다. 따라서 원전의 방사화된 생물학적 차폐 콘크리트를 비롯하여 철근 콘크리트 구조물 해체 작업 시 절단 장비로서 사용될 수 있을 것이다.

• 한국건설순환자원학회논문집
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• 제8권2호
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• pp.167-174
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• 2020

순환 골재 활용에 대한 연구가 국내에서도 비교적 많이 이루어져 왔으나, 대부분 순환 골재의 출처가 명확하지 않아, 국내 원자력 발전소와 같이 출처가 분명한 순환 골재를 재활용하는데 직접적으로 연구 결과를 적용하기에는 많은 불확실성이 존재한다. 따라서, 이 연구에서는 국내 원자력발전소 해체 시 발생하는 콘크리트 폐기물로부터 순환 굵은 골재를 생산 및 재활용할 수 있는 가능성에 대해 분석하기 위해, 국내 원자력발전소 모의 콘크리트를 제작 후 순환 굵은 골재를 생산하였다. 생산된 순환 굵은 골재를 활용하여 순환 굵은 골재 혼입률을 고려한 콘크리트를 배합하고, 역학적 특성을 실험적으로 분석하였다. 실험 결과 순환 굵은 골재 혼입률이 증가할수록 콘크리트 압축강도, 인장강도, 탄성계수 모두 전반적으로 감소하는 것으로 나타났으며, 순환 굵은 골재만을 사용한 경우 일반 콘크리트 대비 각각 최대 36, 37, 27% 정도로 감소하는 것으로 나타났다. 따라서, 향후 원자력발전소 해체로부터 생산된 순환 굵은 골재를 활용할 경우 혼입률에 대한 제한이 필요할 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.865-872
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• 2017

For more than 10 years, the laser process has been studied for dismantling work; however, relatively few research works have addressed the effect of high-power fiber laser cutting for thick sections. Since in the nuclear sector, a significant quantity of thick material is required to be cut, this study aims to improve the reliability of laser cutting for such work and indicates guidelines to optimize the cutting procedure, in particular, nozzle combinations (standoff distance and focus position), to minimize waste material. The results obtained show the performance levels that can be reached with 10 kW fiber lasers, using which it is possible to obtain narrower kerfs than those found in published results obtained with other lasers. Nonetheless, fiber lasers appear to show the same effects as those of $CO_2$ and ND:YAG lasers. Thus, the main factor that affects the kerf width is the focal position, which means that minimum laser spot diameters are advised for smaller kerf widths.

• 방사성폐기물학회지
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• 제16권3호
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• pp.377-387
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• 2018

대한민국 첫 상업원전인 고리1호기는 40년간의 성공적인 운전을 끝내고 2017년 6월 18일 영구정지 되었다. 고리1호기는 본격적인 해체에 앞서 터빈건물에 폐기물처리시설 건설을 계획하고 있다. 각종 방사성폐기물은 폐기물처리시설에서 제염, 해체, 절단, 용융되어 자체처분 되거나 방사성폐기물 처분장으로 보내 진다. 해체폐기물 중 대형금속방사성폐기물은 주로 1차 계통측 기기들로 높은 방사능을 띄고 있어 해체활동 중 작업자의 피폭관리가 필요하다. 본 논문에서는 대형금속방사성폐기물 중 크기가 가장 크고 형상이 복잡한 증기발생기를 선정하여 RESRAD-RECYCLE 코드를 이용하여 작업자 피폭선량을 평가하고 저감화 방안을 수립 하고자 한다.

• 방사성폐기물학회지
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• 제17권2호
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• pp.139-165
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• 2019

한국원자력연구원에서 개발 중인 해체기술 현황 및 전망에 대해 기술하였다. 특히, 해체의 핵심기술인 제염, 원격절단, 해체 폐기물처리 및 부지 복원 분야를 중점적으로 다루었다. 제염기술로는 부품제염과 원자력시스템제염 부분을 고찰하였고, 원격절단기술 관련해서는 절단기술, 원격제어 및 해체공정 모사기술이 다루어졌다. 해체 폐기물처리기술 관련해서는, 비록 해체 후 다양한 폐기물이 발생하지만, 주 폐기물인 금속, 가연성폐기물과 난처리성 특수 폐기물인 고염 고방사성 폐액, 유기혼성폐기물 및 우라늄 복합폐기물 처리기술 등을 주로 기술하였다. 마지막으로, 해체부지 복원 분야에서는 방사선 측정, 부지재이용의 안전성평가 그리고 부지 복원기술 등을 중점적으로 기술하였다.