• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1830-1837
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• 2023

The thermal cutting of contaminated or activated metals during decommissioning nuclear power plants inevitably results in the release of radioactive aerosol. Since radioactive aerosols are pernicious particles that contribute to the internal dose of workers, air conditioning units with a HEPA filter are used to remove radioactive aerosols. However, a HEPA filter cannot be used permanently. This study evaluates the efficiency and lifetime of filters in actual metal cutting condition using a plasma arc cutter and a high-resolution aerosol detector. The number concentration and size distribution of aerosols from 6 nm to 10 ㎛ were measured on both the upstream and downstream sides of the filter. The total aerosol removal efficiency of HEPA filter satisfies the standard of removing at least 99.97% of 0.3 ㎛ airborne particles, even if the pressure drop increases due to dust feeding load. The pressure drop and particle size removal efficiency at 0.3 ㎛ of the HEPA filter were found to increase with repeated cutting experiments. By contrast, the efficiency of used HEPA filter reduced in removing nano-sized aerosols by up to 79.26%. Altogether, these results can be used to determine the performance guidance and replacement frequency of HEPA filters used in nuclear power plants.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.2
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• pp.157-167
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• 2020

Removing radioactive concrete is crucial in the decommissioning of nuclear power plants. However, this process generates radioactive aerosols, exposing workers to radiation. Although large amounts of radioactive concrete are generated during decommissioning, studies on the internal exposure of workers to radioactive aerosols generated from the cutting of radioactive concrete are very limited. In this study, therefore, we calculate the internal radiation doses of workers exposed to radioactive aerosols during activities such as drilling and cutting of radioactive concrete, using previous research data. The electrical-mobility-equivalent diameter measured in a previous study was converted to aerodynamic diameter using the Newton-Raphson method. Furthermore, the specific activity of each nuclide in radioactive concrete 10 years after nuclear power plants are shut down was calculated using the ORIGEN code. Eventually, we calculated the committed effective dose for each nuclide using the IMBA software. The maximum effective dose of ¹⁵²Eu constituted 83.09% of the total dose; moreover, the five highest-ranked elements (¹⁵²Eu, ¹⁵⁴Eu, ⁶⁰Co, ²³⁹Pu, ⁵⁵Fe) constituted 99.63%. Therefore, we postulate that these major elements could be measured first for rapid radiation exposure management of workers involved in decommissioning of nuclear power plants, even if all radioactive elements in concrete are not considered.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.38-45
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• 2018

The purpose of this study is to deduct the structural damage / work process risks factors which can be occurred during the decommissioning in the NPP containment concrete structure. To achieve these purpose, risk profile specified in the construction industry is analyzed, and the work process of NPP decommissioning and the construction project were matched based on the similarity of each works. Accordingly, human and physical risk factors are classified. Finally, the risk associated with the building structure and work process was classified as per their process activities, and risk typology explaining the disaster which put the structure, equipments, machine and workers in serious danger was developed.

• Journal of radiological science and technology
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• v.47 no.3
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• pp.183-195
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• 2024

Additional functional upgrades to the large-area compton camera (LACC) measurement device that can provide characteristics evaluation information (nuclear species and radioactivity) and two-dimensional or three-dimensional distribution imaging information of radioactive materials existing in surface or internal of concrete structures are required in terms of work stability and efficiency in order to apply to actual decommissioning sites such as nuclear power plants or medical cyclotron facilities by using this measurement device. To this purpose, the technology that allows radiation workers to intuitively and visually check the distribution of radioactive materials in advance by matching the two-dimensional distribution imaging information of radioactive materials obtained through the LACC measurement device and visual imaging of the measurement zone (10 m × 5 m) was developed. In addition, the separate system that can automatically adjust the position (height) in units of the measurement area size (0.7 m × 0.3 m × 0.8 m) of the LACC measurement device was developed and the integrated management system for characteristics evaluation information and two-dimensional or three-dimensional distribution imaging information obtained per unit of measurement for radioactive materials was developed. These functional upgrades related to LACC measurement device can improve work efficiency and safety when measuring radioactivity of concrete structures and enable the establishment of appropriate decommissioning strategies using radioactivity measurement information for decommissioning nuclear power plants or medical cyclotron facilities.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.2019-2024
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• 2021

For evaluating the radiological safety of dismantled concrete, the process of disposal and recycling of the radioactive concrete generated during the dismantling of Kori Unit 1 is analyzed. Four scenarios are derived based on the analysis of the concrete recycling and disposal process, and the potential exposure to the workers and public during this process are calculated. VISIPLAN and RESRAD code are used for evaluating the dosages received by the workers and public in the following four scenarios: concrete inspection, transport of concrete by the truck driver, driving on a recycled concrete road, and public living near the landfilled concrete waste. Two worker exposure scenarios in the processing of concrete and two public exposure scenarios in recycling and disposal are considered; in all the scenarios, the exposure dose does not exceed the annual dose limit for each representative.

• Nuclear Engineering and Technology
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• v.44 no.5
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• pp.507-522
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• 2012

When decommissioning a nuclear power plant, it is difficult to make an appropriate plan to ensure sufficient space for temporary placement and conveyance operations of dismantling targets. This paper describes a system to support temporary placement and conveyance operations using augmented reality (AR). The system employs a laser range scanner to measure the three-dimensional (3D) information of the environment and a dismantling target to produce 3D surface polygon models. Then, the operator simulates temporary placement and conveyance operations using the system by manipulating the obtained 3D model of the dismantling target in the work field. Referring to the obtained 3D model of the environment, a possible collision between the dismantling target and the environment is detectable. Using AR, the collision position is presented intuitively. After field workers evaluated this system, the authors concluded that the system is feasible and acceptable to verify whether spaces for passage and temporary storage are sufficient for temporary placement and conveyance operations. For practical use in the future, some new functions must be added to improve the system. For example, it must be possible for multiple workers to use the system simultaneously by sharing the view of dismantling work.

• Nuclear Engineering and Technology
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• v.48 no.6
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• pp.1368-1375
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• 2016

A radiological safety assessment study was performed for the transportation of low level radioactive wastes which are temporarily stored in Korea Atomic Energy Research Institute (KAERI), Daejeon, Korea. We considered two kinds of wastes: (1) operation wastes generated from the routine operation of facilities; and (2) decommissioning wastes generated from the decommissioning of a research reactor in KAERI. The important part of the radiological safety assessment is related to the exposure dose assessment for the incidentfree (normal) transportation of wastes, i.e., the radiation exposure of transport personnel, radiation workers for loading and unloading of radioactive waste drums, and the general public. The effective doses were estimated based on the detailed information on the transportation plan and on the radiological characteristics of waste packages. We also estimated radiological risks and the effective doses for the general public resulting from accidents such as an impact and a fire caused by the impact during the transportation. According to the results, the effective doses for transport personnel, radiation workers, and the general public are far below the regulatory limits. Therefore, we can secure safety from the viewpoint of radiological safety for all situations during the transportation of radioactive wastes which have been stored temporarily in KAERI.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.2
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• pp.171-178
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• 2014

After the expiration of operating license of a plant, all infrastructures within the plant must be safely dismantled to the point that it no longer requires measures for radiation protection. Despite the fact that Kori 1 and Wolsong 1 are close to the expiration of their operating license, sufficient technologies for radiological characterization, decontamination and dismantling is still under development. The purpose of this study is to develop one of methods for radiological inventory assessment on measuring object by using direct measure of large component with In-Situ measurement technique. Radiological inventory was assessed by analyzing nuclide using portable gamma spectroscopy without dismantling reactor head, and the result of direct measurement was supplemented by performing indirect measurement. Radiochemical analysis were performed on surface contamination samples as well. During the study, radiological inventory of reactor vessel calculated expanding the result. Based on the result and the radioactivity variation of each radionuclides time frame for decommissioning can be decided. Thus, it is expected that during the decommissioning of plants, the result of this study will contribute to the reduction of radiation exposure to workers.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3293-3298
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• 2022

Removing radioactive contaminated metal materials is a vital task during the decommissioning of nuclear power plants to reduce the cost of the post-dismantling process. The laser decontamination technique has been recognized as a key tool for a successful dismantling process as it enables a remote operation in radioactive facilities. It also minimizes exposure of workers to hazardous materials and reduces secondary waste, increasing the environmental friendless of the post-dismantling processing. In this work, we present a thorough and efficient laser decontamination approach using a single-mode continuous-wave (CW) laser. We subjected stainless steels to a surface-removal process that repetitively exposes the laser to a confined region of ~75 ㎛ at a high scanning rate of 10 m/s. We evaluate the decontamination performance by measuring the removal depth with a 3D scanning microscope and further investigate optimal removal conditions given practical parameters such as the laser power and scan properties. We successfully removed the metal surface to a depth of more than 40 ㎛ with laser power of 300 W and ten scans, showing the potential to achieve an extremely high DF more than 1000 by simply increasing the number of scans and the laser power for the decontamination of primary circuits.

• Journal of Radiation Industry
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• v.17 no.3
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• pp.239-256
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• 2023

The classification of the radiation work performed in Korean nuclear power plants (NPPs) must be understood to provide workers with more comprehensive radiation protection. This study used annual reports on occupational exposure to investigate and analyze the similarities and differences in the radiation work performed in Korean NPPs with pressurized water reactors (PWRs) and pressurized heavy water reactors (PHWRs). The results showed that the radiation work performed in Korean NPPs could be classified into three categories. Category 1 contains work at the highest level. This work can be divided into individual tasks belonging to Category 2, which enables the evaluation of the radiation dose during the work. The work in Category 2 consists of tasks from Category 3, which contains basic detailed tasks that are not further subdivided. This study emphasized the need for the systematic management of the radiation work performed in both Korean PWRs and PHWRs, such as the tasks in Category 3, which are similar, with similar working conditions, for PWRs and PHWRs. It also suggested the need to establish a list of radiation work for decommissioning because Kori Unit 1 and Wolsong Unit 1 are currently in permanent shutdown and preparations are being made for their decommissioning.