Due to the saturation of the on-site storage capacity of spent nuclear fuel within a few years, dry storage facility should be introduced. However, it is unclear when to start operating the dry storage facility, so in case of Kori Unit 1, which is being decommissioning, the spent fuel must be stored in the spent fuel pool of another power plant. In addition, in the case of damaged fuel, it is impossible to transfer and store it with general handling methods. Therefore, a damaged fuel canister (DFC) should be able to handle damaged or failed fuel as intact fuel, and both wet and dry storage should be possible. The canister developed by Korea Hydro & Nuclear Power is designed to satisfy criticality, shielding, cooling performance, and structural integrity in accordance with NUREG-1536 and 2215. In addition, it can be handled as existing fuel handling devices rather than new handling tools. Fastening of the DFC lid and body in the spent fuel pool is possible with a hexagonal socket wrench, one of the fuel repair tools. And it is designed to facilitate visual identification of whether it is fastenedor not. The lifting method for transferring DFC to another facility is the same as the nuclear fuel lifting method. And a unique sealing and mesh structure of the lid and body is devised to completely block leakage of nuclear fuel fragments of 0.2 mm or more during vacuum drying for dry storage. The usability of DFC has been verified through test operation of the prototype, and it will be manufactured before discharging spent fuel for the decommissioning of Kori Unit 1.

Currently, as the saturation capacity of wet storage pool for spent nuclear fuel (SNF) of PWR in Korea has reached approximately 75%, Dry Storage Facilities (DSF) are necessary for sustainable operation of nuclear power plants. It is necessary to develop acceptance requirements for the delivery of SNF from reactor storage site to Centralized DSF. To do this end, the mechanical integrity of SNF is directly related to its repacking, retrieving, and transporting/handling performances. And also, this integrity is a key factor associated with the criticality safety that is connected to the damaged status of SNF. According to the NUREG/CR-6835, the NRC expects that the potential for nuclear fuel failures will increase because of the increase of the fuel discharge burnup and the degradation of fuel and clad material properties. Due to such damages and/or degradation, the fuel rods in the fuel assembly may be extracted and empty for following treatments (transportation, storage, handling etc). This condition can have a detrimental effect on the criticality safety of SNF. Thus, this study investigated whether extracted and empty of damaged SNF rod affects criticality safety. In this analysis, it is assumed that up to four fuel rods are missed. As a result of the analysis, As the number of fuel rods miss up to a certain number, the value of multiplication factor value of the fuel assembly increases. In addition, since the fuel rods located at the outermost layer contained relatively less fissile material than the fuel rods located center of the lattice, and neutrons were lost by the absorption material, the effective multiplication factor value gradually decreased. Nevertheless, the criticality safety was assessed to be maintained.

As the zircaloy cladding absorbs an excessive amount of hydrogen and cooled down under hoop stress, radial hydride may be precipitated by hydride reorientation phenomenon. There have been many previous studies about the threshold stress of the reorientation, but it is known that the quantitative degree of hydride reorientation rather than the threshold is important for the prediction of mechanical properties. A thermodynamic model for Radial Hydride Fraction (RHF) prediction has been developed in this study. The model calculates RHF with respect to temperature, cooling rate, hydrogen content, and applied stresses. Once the cooling rate is given, the solid solution concentration at each temperature is determined by Hydrogen-Nucleation-Growth-Dissolution model. Subsequently, the increment of radial hydride is derived by nucleation and growth theory. The code based on the thermodynamic theory can provide the prediction of RHF under hoop stress, as well as a change in precipitation behavior over time. RHF of the zircaloy cladding in long-term dry storage can be obtained by the implementation of the code and the degradation of the cladding is directly estimated according to the correlation between RHF and mechanical properties. Ongoing experimental validation of the developed model is discussed.

As the saturation rate of temporary storage facilities for spent nuclear fuel increases, regulatory demands such as interim storage and permanent disposal of spent nuclear fuel are expected to begin in earnest. Considering the domestic situation where all nuclear power plants are located on the waterfront site, the interim storage site is also likely to be located on the waterfront site, and maritime transportation is one of the essential management stages. Currently, there are no independently developed maritime transportation risk assessment code in Korea, and no research has been conducted to evaluate the release of radioactive waste due to the sinking of transport container. Therefore, it is necessary to secure technology to properly reflect the domestic maritime transportation environment and to assess the impact of the sinking accident and to carry out safety regulations. To accurately calculate the releaser rate of radionuclides contained in a cask with breached containment boundary, the flow rate through the gap generated in the containment boundary should be calculated. The fluid flow through this gap which is probably in micro scale in most situations should be evaluated combining the fluid flow inside and outside the cask. In this study, a detailed computational fluid dynamics model to evaluate the internal fluid flow in the cask and a simplified model to capture the fluid flow and the heat transfer around the cask in the sea are constructed. The results for the large scale model are compared with the analytic formula for verification of heat transfer coefficient and they showed good agreements. The heat transfer coefficient thus found can be used in the detailed model to provide more realistic data than those obtained from assumed heat transfer coefficient around the surface of the cask. In the future, fluid flow through the gap between the lid and the body of the cask will be evaluated coupling the models developed in this work.

Material balance evaluation is an important measure to determine whether or not nuclear material is diverted. A prototype code to evaluate material balance has been developed for uranium fuel fabrication facility. However, it is difficult to analyze the code’s functionality and performance because the utilization of real facility data related to material balance evaluation is very limited. It is also restricted to deliberately implement various abnormal situations based on real facility data, such as nuclear diversion condition. In this study, process flow simulator of uranium fuel fabrication facility has been developed to produce various process data required for material balance evaluation. The process flow simulator was developed on the basis of the Simulink-SimEvents framework of the MathWorks. This framework is suitable for batch-based process modeling like uranium fuel fabrication facility. It dynamically simulates the movement of nuclear material according to the time function and provides process data such as nuclear material amount at inputs, outputs, and inventories required for Material Unaccounted For (MUF) and MUF uncertainty calculation. The process flow simulator code provides these data to the material balance evaluation code. And then the material balance evaluation code calculates MUF and MUF uncertainty to evaluate whether or not nuclear material is diverted. The process flow simulator code can simulate the movement of nuclear material for any abnormal situation which is difficult to implement with real process data. This code is expected to contribute to checking and improving the functionality and performance of the prototype code of material balance evaluation by simulating process data for various operation scenarios.

For national security, approximately 500 facilities have been designated as national security facilities. It is divided into grades A, B, and C depending on the fields such as electrics, energy and public service. In 2016, KINAC developed and suggested the installation standards and evaluation indicators for security equipment for national security facilities and they have been utilized to evaluate and manage the facilities. In order to update them by reflecting the recent security trend of the facilities and new technology, KINAC have investigated and updated the installation standards and evaluation indicators for security equipment. As a part of developing installation standards and evaluation indicators for national security facilities project, we conducted survey to identify the status and capabilities of facilities: how the security system is well designed, which type of security equipment is utilized. According to the results, the passive infrared (PIR) sensor is commonly used for interior intrusion detection (not included in 2016 project). Therefore, we investigated the passive infrared sensor and provided its installation standards and evaluation indicators. PIR sensor detects the energy generated by the objects which is different as their temperatures. PIR sensors do not emit any energy like active infrared sensor, and do not measure the energy. Rather, PIRs measure variation in thermal radiation. PIR sensor detects thermal energy by sensing the change between a heat source and the background temperature. In this paper, the characteristics and features of PIR sensor were discussed. Considering them, the standards and indicators to install/evaluated the PIR sensors were also proposed. The results would support national security facility to design and evaluate their security system.

The bilateral nuclear cooperation agreement provides the basis for technical and economic exchanges and research and development cooperation in the nuclear industry, while also having an important role in the peaceful use of nuclear power. The government of Republic of Korea has signed the supplementary and additional arrangements with the United States, Canada, and Australia to specify detailed procedures necessary for the implementation of the agreement. Currently, items under the bilateral nuclear cooperation agreement (i.e., obligated items) are managed through official documents and e-mails, and it is difficult for the government to systemically track item inventory and identify the person in charge. Another issue is the discrepancy of information between the annual report on obligated items and the report under the import and export procedure. In order to solve these problems, the government is establishing an import and export management system for obligated items to enhance transparency and national reliability in Korea. The ultimate purpose of this project is to not only faithfully fulfill the obligations under the bilateral nuclear cooperation agreement, but also to increase the efficiency of implementation work through systematization of databases and management of obligated items. In this paper, an improved management procedures are suggested by analyzing the required functions and problems. Also, this paper provides a conceptual design that can be applied to the management system for it obligated items by identifying and analyzing practical problems in the import and export management of mandatory items. As a result, key considerations and the conceptual design proposal for the ‘export and import management system for items subject to the nuclear bilateral cooperation agreement’ are derived. The result will be supplemented through continuous discussions with facility operators and the government to be utilized for detailed system design.

For countering nuclear proliferation, satellite imagery is being used to monitor suspicious nuclear activities in inaccessible countries or regions. Monitoring such activities involves detecting changes over time in nuclear facilities and their surroundings, and interpreting them based on prior knowledge in terms of nuclear proliferation or weaponisation. Therefore, analysts need to acquire and analyze satellite images periodically and have an understanding of nuclear fuel cycle as well as expertise in remote sensing. Meanwhile, as accessibility of satellite information has been increasing and accordingly a large amount of high-resolution satellite images is available, a lack of experts with expertise in both fields to perform satellite imagery analysis is being concerned. In this regard, the Institute of Korea Nonproliferation and Control (KINAC) has developed a prototype of semi-automatic satellite imagery analysis system that can support monitoring of potential nuclear activities to overcome the limitations of professionals and increase analysis efficiency. The system provides a satellite imagery database that can manage acquired images, and the users can load images from the database and analyze them in stages. The system includes a preprocessing module capable of resizing, correcting and matching images, a change detection module equipped with a pixel-object-based change detection algorithm for multi-temporal images, and a module that automatically generates reports with relevant information. In particular, this system continuously updates open-source information database related to potential nuclear activities and provides users with an integrated analytics platform that can support their interpretation by linking related images and textual information together. As such, the system could save time and cost in processing and interpreting satellite images by providing semi-automated analytic workflows for monitoring potential nuclear activities.

Nuclear power plants, like other national critical infrastructures, could be under the threat of terrorism or other malicious action. Thus, a nuclear power plant has a robust security system that includes security guards, sensors, barriers, access control systems, lights, and alarm stations with security procedures. However, an effective security system is hard to design because a chain is only as strong as its weakest link, and there could be a vulnerable hole even in the robust security system. Thus, an effective security system requires the evaluation of all possible scenarios. Evaluation software for security system effectiveness assists in systematically assessing all the possible attack scenarios. Many countries developed security effectiveness evaluation software. The first software was developed by the U.S. Sandia National Laboratories in the 1980s. Now there are several commercially available software packages with a function to simulate limited-scope combat between security guards and attacking enemies. However, academic communication is comparatively weak because it may contain sensitive information on the vulnerability of nuclear power plants. We developed original software called Tools for Evaluating Security Systems (TESS) to identify the most vulnerable path to the designated target and model the security systems of all South Korean nuclear power plants. We also used commercial security effectiveness evaluation software, AVERT, to model the same nuclear power plants. TESS was developed to verify the results of commercial security effectiveness evaluation software for the purpose of regulatory use. For the feasibility test, we compared the results of two software with those of force-on-force (FoF) exercises in nuclear power plants. According to the relevant Act, every nuclear power plant site should perform the FoF exercises every year. KINAC was in charge of evaluating the FoF exercise and used several of its results for the study. In the results, even in some differences in detail, the two software and FoF exercises showed qualitative similarity. Conclusively, evaluation software is a useful tool to design and/or assess the security systems of nuclear power plants. We modeled the security systems of all South Korean nuclear power plants, and compared the developed software, a commercial software and FoF exercises. The results showed qualitative similarity. We provided the results of evaluation to nuclear operators for the better security of nuclear power plants.

Recently, extreme terrorist attacks have frequently occurred around the world and are threatening the international community. It is no longer a safe zone for terrorism in our country. Therefore, domestic nuclear facilities as the highest level of national security facilities have established a physical protection system to protect facilities and lives against terrorist attacks. In addition, security search and access control are conducted for controlled items and unauthorized person. However, with the development of science and technology, disguised weapons or homemade explosives used in terrorism are becoming very sophisticated. Therefore, nuclear facilities need to strengthen security search of weapons or homemade explosives. Since these disguised weapons or homemade explosives are difficult to find only through security search, it is also necessary to actively identify unspecified people who possess disguised weapons or do abnormal behavior. For this reason, the “Abnormal Behavior Detection Method”, which is very effective in preemptive response to potential terrorist risks, has been introduced and operated in aviation security field. Korea Institute of Nuclear Nonproliferation and Control (KINAC) has established a “Practice Environment for Identifying Disguised Weapons” in 2020 for trainees to recognize the dangers of controlled items and to use for physical protection education. This Practice environment has not only the basic explanation of the controlled items of nuclear facilities, but also various actual disguised weapons were displayed. It also introduces actual terrorist incidents using homemade explosives such as attempted bombing of a cargo plane bound for Chicago and the Boston Marathon bombing. And then a model of the disguised explosives actually used is displayed and used for education. In addition, in 2022, the “Abnormal behavior detection method” education module was developed and used for physical protection education. In this module, the outline and introduction of the “Abnormal Behavior Detection Method” and “Behavior Detection Officer (BDOs)” are explained. In this way, the access control and security search system of nuclear facilities require the overall monitoring system, not only for dangerous goods but also for identification of persons possess and carrying them. This study describes the development of the Curriculum for “Disguised Weapon Identification” and “Abnormal Behavior Detection Method” to enhance the effectiveness of physical protection education.