The Korean administration assumed that the amount of low and medium level waste generated during the decommissioning of nuclear facilities in Korea was 14,500 drums (based on 200 L) and designed the LILW repository accordingly. Accordingly, it is necessary to separate the nuclear power plant decommissioning waste into clearance waste by mobilizing means such as decontamination and cutting as much as possible, and to deregulate it together with non-radioactive waste. As a result, clearance waste and non-radioactive waste are dominated by concrete and metal, and it is necessary to evaluate how to recycle them. Many existing studies have conducted research on each recycling method, and accordingly, it can be judged that the technological maturity is sufficient. Accordingly, we would like to propose a method for comprehensive management and evaluation of concrete. By applying the decision matrix proposed in IAEA TRS No. 401, it will be possible to compare the 5 factors (cost, technical feasibility, risk, availability of disposal, and full cycle impact). However, in the case of concrete, if the existing construction waste recycling methodologies are fully used, the technical feasibility can be considered equal. Therefore, it was judged that it would be good to introduce the aspect of public acceptance as an evaluation item instead of technical feasibility. The amount of waste that can be generated when decommission a nuclear power plant is only insignificant compared to the total amount of waste concrete that is generated during the year. Accordingly, one option is to fully integrate the waste concrete recycling system and utilize it for road construction. Next, it is possible to suggest the option of recycling in the construction of shields in the nuclear industry, as suggested in previous studies, and the method of using it as a backfill material such as for a decommissioned NPP site or other sites. As an example, and a draft stage, this study was evaluated based on existing studies after all options were equally weighted. When the profit and loss was evaluated in a way that a maximum of 5 points were given to each option, the case of using it as a backfill in various applications was evaluated as the best option. Unlimited recycling, such as road construction, was evaluated to be highly damaging in terms of public acceptance.

3D modeling is a technology for representing real objects in a virtual 3D space or modeling and reproducing the physical environment. 2D drawings for viewing the existing building structure have limitations that make it difficult to understand the structure. By implementing this 3D modeling, specific visualization became possible. 3D technology is being applied in a wide range of preevaluation work required for nuclear decommissioning. In Slovakia, 3D modeling was applied to determine the optimal cutting strategy for the primary circuit before dismantling the VVER type Bohunice V1. In Japan, the Decommissioning Engineering Support System (DEXUS) program has been developed that incorporates VRDose, a decommissioning engineering support system based on 3D CAD models. Through this, the cutting length of the work object and the quantity of containers for packaging waste are calculated, exposure dose calculations in various dismantling scenarios, and cost estimation are performed. Korea also used 3D technology to evaluate the decommissioning waste volume for Kori Unit 1 and to evaluate the optimal scenario of the decommissioning process procedure for the research reactor Unit 1. 3D technology is currently being used in various pre-decommissioning evaluations for VVER, PWR, and research reactors. Overseas, a program that matches various decommissioning pre-evaluation tasks with cost estimation has also been developed. However, most 3D technologies are mainly used as a support system for dose evaluation and amount of decommissioning waste calculation. In this study, 3D modeling was performed on the PHWR structure, and physical and radiological information about the structure was provided. The information on the structure can present the unit cost for the work object by confirming the standard of the applied unit cost factor (UCF). The UCF presents the unit cost for repeated decommissioning operations. The decommissioning cost of the work object can be obtained by multiplying the UCF by the number of repetitions of the work. If the results of this study are combined with the process evaluation and waste quantity estimation performed in previous studies, it is judged that it will be helpful in developing an integrated NPP decommissioning program that requires preliminary evaluation of various tasks. In addition, it is judged that a clear cost estimation of the object to be evaluated will be possible by matching the 3D work object with the UCF.

Radioactive waste is classified into Intermediate level, low level, and very low potential based on the amount of radioactivity per unit gram, that is, the concentration limit. This method of classifying radioactivity per unit weight is not a problem if all packaged wastes are homogeneous. However, the reality is that not all waste is homogeneous. Relative hotspots may exist. Also, when several items are mixed, if one item has a relatively higher concentration than other items, it can become a relative hotspot. In Korea, even if all nuclides in a single radioactive waste package satisfy the low level concentration limit, if even one nuclide exceeds the concentration limit, the radioactive waste package becomes the intermediate level. In case of the United States, the US NRC provides regulations related to obtaining license as well as presents the technical position on the average waste concentration called Concentration Averaging and Encapsulation Branch Technical Position (CA BTP). CA BTP classifies waste into four types : Blendable Waste, Encapsulated items, Single Discrete Items, and Mixture of Discrete Items, and presents each approach to concentration averaging. In general, this is a method that suggests an acceptable ratio in case of the waste, which relatively high concentration waste is mixed. In order to apply this in Korea, we compare the classification standards for low and Intermediatelevel waste in Korea and the United States, related laws and backgrounds, and the application methods of CA BTP.

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.

It is necessary to prepare for cutting and storing waste materials in the reactor vessel internals (RVI) for successful decommissioning of the nuclear power plant (NPP). Since RVI contain massive components and relatively highly activated, their decommissioning process should be conducted carefully in terms of radiological and industrial safety. To achieve efficient decommissioning waste management, this study presents radiation level of RVI and cutting optimization was performed for intermediate level waste. As a result of the radiation evaluation, a part of the core side and the upper part of RVI were evaluated as intermediate-level waste, and other components were evaluated as very low-level or lowlevel waste. For intermediate-level waste cutting, the minimum cutting method that can be put into a container was reviewed in consideration of the size, thickness, and cutting method of the interior product. The final segmentation parts are expected to be loaded into two storage containers.

The saturation rates of the spent fuel (SF) wet storage at the Kori Nuclear Power Plant (NPP), Hanbit, and Hanul are 83.3%, 74.2%, and 80.8% as of the fourth quarter of 2021. The storages of Kori NPP and Hanbit NPP are expected to be saturated in 2031, and Hanul is expected to be saturated in 2032. Therefore, the construction of an interim storage facility to store the SF temporarily stored in the NPP was planned, and preparations for the safe transport of the SF are required. In this paper, radiological preliminary assessment using NRC-RADTRAN in the process of sea transport of SF from the wet storage or ISFSI of the Hanbit NPP to the optional interim storage facility was performed. Since domestic SF transport vessels are not currently in operation, the specifications of the UK Pacific Grebe vessel which can carry up to 20 casks were used. The transport cask used the specifications of KORAD-21, a transport container developed in Korea. Because it can carry more SF assemblies than the existing KN-18. In addition, a land transport safety test was conducted in 2020 and a sea transport test is planned. The sea transport route was entered by referring to the transport route of domestic low and intermediate level waste. The accidents rate was calculated using statistics on maritime accidents from 2017 to 2021. The probability accidents along the transportation route were evaluated as 3.152E -10. When transporting to an interim storage facility, the SF expected to be the main transport target was selected as WH 17X17, combustion 45,000 MWD/MTU, and concentration of 4.5%. The source term was calculated and entered according to this data and the release fraction was entered with reference to the DOE report. In the case of normal transport without accident, the individual dose of the crew member and public residents were estimated to be 0.0525% and 0.000492% of the annual limit of 1 mSv/yr for the general public. Under the accident conditions, the annual individual doses of residents were 0.0011%, 0.0023%, 0.0034%, and 0.0046% of the annual limit of 1 mSv/yr when carrying 5, 10, 15, and 20 casks. Currently, the site of the interim storage facility has not been precisely determined, but a preliminary radiation assessment through sea transport resulted in a significantly lower than the limit. Combined scenario sea transport followed by land transport will be carried out in the next stage of study.

This paper mainly focuses on the maximum decay heat estimation generated from spent fuel assemblies in the spent fuel pool of Kori units 3&4 at the beginning decommissioning. It is assumed that the spent fuel pool is fully occupied with 2,260 spent fuel assemblies, same as its design capacity. In addition, equally 56.5 spent fuel assemblies have been generated per year. The minimum cooling time is five years considering the transition phase between the permanent shutdown and the amendment of Operating License for decommissioning. Sending and receiving of spent fuel assemblies to/from other units are neglected. Seven representative spent fuel assembly groups are established based on the burnup rate and cooling time. Conservatively high values for the burnup rates and low values for the cooling times are applied. Calculation of the decay heat of each representative group has been performed by using ORIGEN decay solver of SCALE. Then, total decay heat has been calculated based on this. Group 1, 2, and 3 contain comparatively old spent fuel assemblies with 45 GWd/tU burnup rate and 20~30 cooling years. The calculation shows 489~586 watts of decay heat per assembly. Group 4, 5, 6, and 7 contain comparatively new spent fuel assemblies with 55 GWd/tU burnup rate and 5~20 cooling years. The calculation shows 741~1,483 watts of decay heat per assembly. The total maximum decay heat therefore is estimated as 1,609,459 watts.

Operating and decommissioning nuclear power plants generates radioactive waste. This radioactive waste can be categorized into several different levels, for example, low, intermediate, and high, according to the regulations. Currently, low and intermediate-level waste are stored in conventional 200-liter drums to be disposed. However, in Korea, the disposal of intermediate-level radioactive waste is virtually impossible as there are no available facilities. Furthermore, large-sized intermediate- level radioactive waste, such as reactor internals from decommissioning, need to be segmented into smaller sizes so they can be adequately stored in the conventional drums. This segmentation process requires additional costs and also produces secondary waste. Therefore, this paper suggests repurposing the no-longer-used spent nuclear fuel casks. The casks are larger in size than the conventional drums, thus requiring less segmentation of waste. Furthermore, the safety requirements of the spent nuclear fuel casks are severer than those of the drums. Hence, repurposed spent nuclear fuel casks could better address potential risks such as dropping, submerging, or a fire. In addition, the spent nuclear fuel casks need to be disposed in compliance with the regulations for low level radioactive waste. This cost may be avoided by repurposing the casks.

Radioactive materials from nuclear power facilities can be released into the atmosphere through various channels. Recently, the dispersion of radioactive materials has become critical issue in Korea after Kori Unit 1 and Wolsong Unit 1 were permanently shut down. In this study, annual atmospheric dispersion factors were compared based on the continuous release and purge release using the XOQDOQ computer program, a method for calculating atmospheric dispersion factors at commercial nuclear power stations. The meteorological data analyzed in this study was based on the Shin Kori nuclear power meteorological tower which has the largest operating nuclear power plants in Korea, for three years (from 2008 to 2010). The analysis results of the dispersion factor of the radioactive material release obtained using the XOQDOQ program showed that the difference between the continuous release and purge release was within two times. This study will be valuable helpful for revealing the uncertainty of the predictive atmospheric dispersion factor to achieve regulation.

Unit 1 of the Kori Nuclear Power Plant (NPP) and Unit 1 of the Wolsong NPP are being prepared for decommissioning; their decommissioning is expected to generate large amounts of intermediate-level, low-level, and very low level Waste. Mixed waste containing both radioactive and hazardous substances is expected to be produced. Nevertheless, laws and regulations, such as the Korean Nuclear Safety Act and Waste Management Act, do not define clear regulatory guidelines for mixed waste. However, the United States has strictly enforced regulations on mixed waste, focusing on the human health and environmental effects of its hazardous components. The U.S. Nuclear Regulatory Commission and the U.S. Department of Energy regulate the radioactive components of mixed waste under the Atomic Energy Act. The U.S. Environmental Protection Agency regulates the hazardous waste component of mixed waste under the Resource Conservation and Recovery Act. In this study, the laws, regulations, and authorities pertaining to mixed waste in the United States are reviewed. Through comparison and analysis with waste management laws and regulations in Korea, a treatment direction for mixed waste is suggested. Such a treatment for mixed waste will increase the efficiency of managing mixed waste when decommissioning NPPs in the near future.

A paradigm shift in the government’s energy policy was reflected in its declaration of early closure of old nuclear plants as well as cancellation of plans for the construction of new plants. To this end, unit 1 of Kori Nuclear Power Plant was permanently shut down and is set for decommission. Based on these changes, the off-site transport of spent fuels from nuclear power plants has become a critical issue. The purpose of this study is to develop an optimized method for transportation of spent fuels from Kori Nuclear Power Plant’s units 1, 2, 3, and 4 to an assumed interim storage facility by simulating the scenarios using the Flexsim software, which is widely used in logistics and manufacturing applications. The results of the simulation suggest that the optimized transport methods may contribute to the development of delivery schedule of spent fuels in the near future. Furthermore, these methods can be applied to decommissioning plan of nuclear power plants.