KEPCO KPS is the contractor for the full system decontamination (FSD) of Kori Unit 1 and under preparation such as modification, lay out for equipment installation, setting up tie-in/out point for chemical injection and way to pressurize the system, of its successful performance. In this research, KPS introduced how KPS has designed and prepared for the FSD project and how will the chemical decontamination process be implemented. As described in the previous research, chemical decontamination process is planned to be conducted for three cycles and each cycle is consisted of oxidation, reduction, decomposition, and purification. Oxidation and reduction process were conducted at 90°C. Chemical decomposition and purification process were conducted at 40°C due to the damage of IX by the heat. If the decontamination result does not meet the target DF and the dose rate, additional cycle can be conducted. Expected volume of process water for FSD is 200 m3. Three systems have been designated as decontamination targets: reactor coolant system (RCS), residual heat removal system (RHRS), chemical volume control system (CVCS). For the steady flow rate, existed plant equipment such as reactor coolant pump (RCP) will be operated and modifications on some components will be conducted. Due to the limited space for installation, decontamination equipment and other resources are distributed to three different places. KPS designed the layout of equipment installed inside the containment vessel. The layout contains the information of shielding for highly radiated equipment such as IX and filter skid.

Derived Concentration Guideline Levels (DCGLs), which represent the residual radioactivity concentration limits, serve as the pivotal criteria for decontamination during decommissioning of nuclear power plants and are essential for license termination. The analysis of radionuclides in various media to check site-specific and radionuclide-specific DCGLs is a resource-intensive and time-consuming processes, and there are some radionuclides that are hard to analyze. In the decommissioning of the Rancho Seco nuclear power plant in the United States, a conservative approach was adopted. Potentially highly contaminated areas on the site were identified by collecting and analyzing soil samples, and radionuclides exceeding the Minimum Detectable Concentration (MDC) were selected as the potential Radionuclide of Concern (ROC), and surrogate DCGLs for hard-to-detect radionuclides were applied to soil samples. For soil samples in the Rancho Seco nuclear power plant, Cs-137 contributed more than 90% of the total radioactivity. DCGLs of the ROC were obtained using the scaling factors through analysis of Cs- 137 for a large amount of soil samples. In Korea, the scaling factor methodology has not been applied to the decommissioning of commercial nuclear power plants. An initial investigation was undertaken to assess the viability of implementing Surrogate Derived Concentration Guideline Levels (DCGLs) in the dismantling of Kori Unit 1, drawing insights from the U.S. nuclear power plant decommissioning experiences. To do this approach, the concentration ratio of radionuclides of interest to key radionuclide in contaminated soil should be known and consistent. But related information is not available at this time. So Surrogate DCGL for representative C-14, Fe-55, Ni-59, Ni-63, and Sr-90 was obtained using the scaling factors applied to radioactive waste data, specifically Decontaminated Aqueous Waste (DAW) and Spent Resin. In order to develop a reliable surrogate DCGLs the Kori Unit 1 site, it is important to analyze the radionuclides in the soil for the Kori Unit 1 decommissioning site to obtain consistent concentration ratio of the radionuclides of concern to the key radionuclides. When a the suitable DCGL is developed, it can be used for FSS planning and prior decision-making ensuring the safe and effective decommissioning of Kori Unit 1 and similar nuclear power plants.

Kori Unit 1 nuclear power plant is a pressurized water reactor type with an output of 587 Mwe, which was permanently shut down on June 18, 2017. Currently, the final decommissioning plan (FDP) has been submitted and review is in progress. Once the FDP is approved, it is expected that dismantling will begin with the secondary system, and dismantling work on the primary system of Kori Unit 1 will begin after the spent nuclear fuel is taken out. It is expected that the space where the secondary system has been dismantled can be used as a temporary storage place, and the entire dismantling schedule is expected to proceed without delay. The main equipment of the secondary system is large and heavy. The rotating parts is connected to a single axis with a length of about 40 meters, and is complexly installed over three floors, making accessibility very difficult. A large pipe several kilometers long that supplies various fluids to the secondary system is installed hanging from the ceiling using a hanger between the main devices, and the outer diameter of the pipe is wrapped with insulation material to keep warm. In nuclear secondary system decommissioning, it is very important to check for radiation contamination, establish and implement countermeasures, and predict and manage safety and environmental risks that may occur when cutting and dismantling large heavy objects. So we plan to evaluate the radiation contamination characteristics of the secondary system using ISOCS (In- Situ Object Counting System) to check for possible radioactive contamination. According to the characteristics results, decommissioning plans and methods for safe dismantling by workers were studied. In addition, we conducted research on how to safely dismantle the secondary system in terms of industrial safety, such as asbestos, cutting and handling of heavy materials and so on. This study proposes a safe decommissioning method for various risks that may occur when dismantling the secondary system of Kori Unit 1 nuclear power plant.

Kori Unit 1, pressurized water reactor, is the Korea’s first commercial nuclear power plant. It successfully generated electricity for a period of 30 years, commencing from April 19, 1978. Following its approval for continued operation in 2008, Kori Unit 1 continued to operate for an additional 9 years, resulting in a total operational period of 39 years. On June 18, 2017, Kori Unit 1 was permanently shut down. Since then, Korea is actively preparing for the decommissioning of nuclear power plant. During the decommissioning of a nuclear power plant, the heavy components such as reactor, steam generator, pressurizer, reactor coolant pump located in the containment building should be taken out of the containment building. To take out heavy components from the containment building, pipes connected to heavy component should be cut. There are numerous pipes connected to the heavy component, each with varying dimensions and material. Each pipe has a different level of contamination depending on its use. In this study, optimal cutting method of pipe connected to steam generator, one of the heavy components of nuclear power plant, is proposed during the decommissioning of Kori unit 1. In case of pipe connected to Kori unit 1 steam generator, material is stainless steel or carbon steel. These pipes have varying inner diameter, ranging from 0.6 cm to 74 cm, and thickness ranging from 0.15 cm to 7.1 cm. These pipes are classified as low and intermediate level waste (LILW) or very low level waste (VLLW). Because characteristics of pipes are different, each pipe optimal cutting methods are proposed differently considering material, dimension, contamination level, cutting cost, cutting time, and the management of secondary waste. As a result, the cutting method for pipe of reactor coolant system is selected to orbital cutting. The cutting method of main steam pipe and main feedwater pipe is selected to oxygen cutting. In case of other small pipes, cutting method is selected to circular saw.

The first commercial operation of Kori-1, which commenced in April 1978, was permanently shut down in June 2017, with plans for immediate dismantling. The decommissioning process of nuclear power plants generates a substantial amount of radioactive waste and poses significant radiation exposure risks to workers. Radioactivity is widely distributed throughout the primary coolant system of the reactor, including the reactor pressure vessel (RPV), steam generator (SG), and pressurizer. In particular, the SG has a considerable size and complex geometry, weighing approximately 326 tons and having a volume of 400 m3. The SG tubes are known to contain high levels of radioactivity, leading to significant radiation exposure to workers during the dismantling process. Therefore, this study aims to evaluate the workers’ radiation exposure during the cutting of SG tubes, which account for approximately 95% of the total radiation dose in the SG. Firstly, the CRUDTRAN code, developed to predict the behavior of soluble and particulate corrosion products in a PWR primary coolant system, is used to estimate the radioactive inventory in the SG tubes. Based on decontamination factors (DF) obtained in the SG tubes through overseas experience, the expected reduction in radioactivity during the Kori-1 reactor’s full-system decontamination (FSD) process is considered in the CRUDTRAN results. These results are then processed to estimate the radioactivity in both the straight and bent sections of the tubes. Subsequently, these radioactivity values are used as inputs for the MicroShield code to calculate the worker radiation exposure during the cutting of both straight and bent sections of the tubes. The cutting process assumes that each SG tube section is cut in a separate, shielded area, and the radiation exposure is assessed, taking into account factors such as cutting equipment, cutting length, working hours, and working distance. This study evaluates the worker radiation exposure during the cutting of SG tubes, which are expected to have a significantly high radioactivity due to chalk river unidentified deposit (CRUD). This assessment also considers the reduction in radioactivity within the steam generator tubes resulting from the FSD process. Consequently, it enables an examination of how worker radiation exposure varies based on the extent of FSD. This study may provide valuable insights for determining the scope and extent of the FSD process and the development of shielding methods during the dismantling of SG tubes in the future.

Compared to operational wastes, nuclear power plant (NPP) decommissioning wastes are generated in larger quantities within a short time and include diverse types with a wider range of radiation characteristics. Currently used 200 L drums and IP-2 type transport containers are inefficient and restrictive in packaging and transporting decommissioning wastes. Therefore, new packaging and transport containers with greater size, loading weight, and shielding performance have been developed. When transporting radioactive materials, radiological safety should be assessed by reflecting parameters such as the type and quantity of the package, transport route, and transport environment. Thus far, safety evaluations of radioactive waste transport have mainly targeted operational wastes, that have less radioactivity and a smaller amount per transport than decommissioning wastes. Therefore, in this study, the possible radiation effects during the transport from NPP to disposal facilities were evaluated to reflect the characteristics of the newly developed containers and decommissioning wastes. According to the evaluation results, the exposure dose to transport workers, handling workers, and the public was lower than the domestic regulatory limit. In addition, all exposure dose results were confirmed, through sensitivity analysis, to satisfy the evaluation criteria even under circumstances when radioactive materials were released 100% from the container.

Kori unit 1, the first PWR (Pressurized Water Reactor) in Korea, was permanent shut down in 2017. In Korea, according to the Nuclear Safety Act, the FDP (Final Decommissioning Plan) must be submitted within 5 years of permanent shutdown. According to NSSC Notice, the types, volumes, and radioactivity of solid radioactive wastes should be included in FDP chapter 9, Radioactive Waste Management, Therefore, in this study, the types depending on generation characteristics and radiological characterization methods and process of solid radioactive waste were analyzed. Solid radioactive waste depending on the characteristics of the generation was classified into reactor vessel and reactor vessel internal, large components, small metals, spent nuclear fuel storage racks, insulation, wires, concrete debris, scattering concrete, asbestos, mixed waste, soil, spent resins and filters, and dry active waste. Radiological characterization of solid radioactive waste is performed to determine the characteristics of radioactive contamination, including the type and concentration of radionuclides. It is necessary to ensure the representativeness of the sample for the structures, systems and components to be evaluated and to apply appropriate evaluation methods and procedures according to the structure, material and type of contamination. Therefore, the radiological characterization is divided into concrete and structures, systems and components, and reactor vessel, reactor vessel internal and bioshield concrete. In this study, the types depending on generation characteristics and radiological characterization methods and process of solid radioactive waste were analyzed. The results of this study can be used as a basis for the preparation of the FDP for the Kori unit 1.

This study presents a methodology to determine the radionuclides of concern that are expected to be found during the final status survey of Kori Unit 1 decommissioning. The methodology involved reflecting the evaluation results of ORIGEN based on reference documents such as NUREG/CR-3474, NUREG/CR-4289, NUREG/CR-0130, WINCO-1191, and representative fuel loading. A list of potential radionuclides of concern was provided by reflecting the list of radionuclides of concern included in the Kori Unit 1 decommissioning plan. To select the radionuclides of concern, we analyzed the approach of US decommissioning plants based on the recommendations of NUREG-1757 Vol.2 Rev.1 and excluded certain radionuclides from the list. The final list of 23 radionuclides of concern was derived by excluding radionuclides that have a short half-life, low specific activity, analytically difficult to measure, inert gases, or naturally occurring radionuclides. This methodology can be applied to other nuclear power plants, such as the Wolsong Nuclear Power Plant, by reflecting the unique characteristics of the reactor.

Kori Unit 1 is about 600MW Pressurized Light Water Reactor as WH type. KHNP got an approval for construction and operation of Kori unit 1 on May 31, 1972 and started commercial operation from Apr. 29, 1987. And then, it was decided to permanently suspend it on Jun. 18, 2017 after 40 years of commercial operation. The Nuclear Safety Act stipulates that if a commercial nuclear power plant is permanently suspended, the utility must submit a Final Decommissioning Plan (FDP) within 5 years. So, KHNP, the utility, developed a FDP for Kori Unit 1 and submitted it to the government in May 2021. In South Korea, the FDP is to be prepared in accordance with the relevant notices and consists of 11 major chapters such as (1) Decommissioning Plan Overview, (2) Project management, (3) Status of Site and Environmental, (4) Decommissioning Strategies and Method, (5) Ease of Decom. Design characteristic, (6) Safety Analysis, (7) Radiation Protection, (8) Decontamination and Dismantling, (9) Radioactive Waste Management, (10) Environmental Impact Analysis, (11) Fire Protection and (12, 13) Etc., References and Glossary. KHNP has prepared a strategy and system consisting of three areas such as R&D, Engineering and licensing document development to prepare the final decommissioning plan for Kori Unit 1. The promotion system for the preparation of the FDP for Kori Unit 1 is composed of Engineering (HAS Characterization, Dismantling Safety Evaluation, Radiological Environmental Report, Radioactive Waste Treatment and Facility Construction), R&D(KHNP R&D Results such as Process/Work Package /Cost Estimation, Safety Analysis, Contamination and Exposure, Guide for Detailed Characteristic, Site Safety Analysis, RV & RVI Dismantling Process, etc.), Overseas case lessons learned(Taiwan unit 1 NPP FDP and Spain Zorita NPP FDP analysis) and Development of Licensing Document. KHNP completed the initial completion of the Final Decommissioning Plan for Kori Unit 1 in March 2020 and carried out collecting residents’ opinions through public hearings. And then, KHNP supplemented the results of the residents’ opinions and applied for license to the Nuclear Safety and Security Commission in May, 2021. Now, KHNP are responding to the FDP licensing review.

Reactor pressure vessels and steam generators generated in the process of dismantling nuclear power plants or replaced steam have various shape and occupy a considerable amount of the disposal site when disposed of in original shape. For the development of domestic technologies related to the disposal of large wastes, it is necessary to secure technologies for reducing large radioactive metal wastes, including technologies such as decontamination, cutting, melting, and residual radioactivity evaluation. Cases of disposal of steam generators in Europe and the United States were investigated. Except for u-tubes, steam generators are less contaminated or easily decontaminated, so it is possible to reduce the volume of waste subject to final disposal by exempting a significant amount through appropriate treatment. Korea Hydro & Nuclear Power Co. is currently temporarily storing 24 steam generators at 41.6 billion won. This paper presents a method to exempt more parts of the steam generator and reduce the volume of waste by properly combining mechanical cutting thermal cutting and melting to dispose of the steam generator. Currently the decontamination and dismantling industries of nuclear facilities are gradually expanding around the world. Therefore, it is necessary to localize the treatment technology for metal waste generated during maintenance and dismantling. The result of this study can be used to establish waste reduction and disposal method for dismantling steam generators.

In operating or permanently shut down nuclear power plants which were built between 1970s and 1990s, asbestos was widely used for ceiling materials, wall materials, and gaskets. Furthermore, it was mainly treated as a heat-resistant material like insulation. In Kori Unit 1, radioactive asbestos was replaced or removed through maintenance and repair in the containment building during the operation period of about 40 years, but radioactive asbestos still remains that need to be partially dismantled. Generally, it is more difficult to handle because it belongs to two different waste categories, radioactive waste and hazardous waste. In addition, the risk increases further due to radioactivity with the asbestos hazards itself. Therefore, it is very important to accurately determine the amount of radioactive asbestos waste and to evaluate the treatment method and disposal reduction rate before the decommissioning is started. According to the Korean Waste Management Act, three methods are recommended for the asbestos (hazardous waste) treatment: landfill, solidification, and high-temperature melting. Landfill is commonly used in Korea and the United States while high-temperature melting and solidification are additionally recommended only in Korea. Considering the situation in Korea, landfill is not appropriate due to the limitations of landfill capacity and potential risks (hazards still remain). Therefore, the other two methods can be considered sufficiently in terms of safety, detoxification, and reduction rate. This paper evaluates the amount of radioactive asbestos waste at Kori Unit 1 based on the actual asbestos building material data (as of February 2022) of the Asbestos Management Comprehensive Information Network. Vitrification is considered as a sufficient alternative for treating radioactive asbestos waste. And, it is checked whether the vitrified waste through the high-temperature melting method, plasma torch, meets the requirements such as detoxification, compressive strength and leachability for storage and disposal stability. It is expected to be useful to prepare a radioactive mixed waste management standard and to reduce the disposal cost through the reduction of final waste.