In the wake of the Fukushima NPP accident, research on the safety evaluation of spent fuel storage facilities for natural disasters such as earthquakes and tsunamis has been continuously conducted, but research on the protection integrity of spent fuel storage facilities is insufficient in terms of physical protection. In this study, accident scenarios that may occur structurally and thermally for spent fuel storage facilities were investigated and safety assessment cases for such scenarios were analyzed. Major domestic and international institutions and research institutes such as IAEA, NEA, and NRC provide 13 accident scenario types for Spent Fuel Pool, including loss-of-coolant accidents, aircraft collisions, fires, earthquakes. And 10 accident scenario types for Dry Storage Cask System, including transportation cask drop accidents, aircraft collisions, earthquakes. In the case of Spent Fuel Pool, the impact of the cooling function loss accident scenario was mainly evaluated through empirical experiments, and simulations were performed on the dropping of spent nuclear fuel assembly using simulation codes such as ABAQUS. For Dry Storage Cask System, accident scenarios involving structural behavior, such as degradation and fracture, and experimental and structural accident analyses were performed for storage cask drop and aircraft collision accidents. To evaluate the safety of storage container drop accidents, an empirical test on the container was conducted and the simulation was conducted using the limited element analysis software. Among the accident scenarios for spent fuel storage facilities, aircraft and missile collisions, fires, and explosions are representative accidents that can be caused by malicious external threats. In terms of physical protection, it is necessary to analyze various accident scenarios that may occur due to malicious external threats. Additionally, through the analysis of design basis threats and the protection level of nuclear facilities, it is necessary to derive the probability of aircraft and missile collision and the threat success probability of fire and explosion, and to perform protection integrity evaluation studies, such as for the walls and structures, for spent fuel storage facilities considering safety evaluation methods when a terrorist attack occurs with the derived probability.

In Korea, additional regulatory requirements are increasing due to the full-scale decommissioning of nuclear power plants following the permanent shutdown of Kori Unit 1 and Wolseong Unit 1. Accordingly, it is necessary to preemptively expand the scope of physical protection regulations from design, construction, and operation stage to back-end nuclear fuel cycle such as cessation of operation and decommissioning. According to Article 2, Paragraph 24 of the Nuclear Safety Act, the decommissioning of nuclear facilities is defined as all activities to exclude them from the application of the Nuclear Safety Act by permanently suspending the operation of nuclear facilities, demolishing the facilities and sites, or removing radioactive contamination. In other words, it refers to a series of technologies or activities to safely and efficiently dismantle nuclear power plant and remove radioactive contamination and restore them to their original state after permanently shut down of nuclear power plant. Security changes during decommissioning and decontamination since removing fuel from the reactor alters the plant’s safety status, some of the systems or components considered as vital equipment during plant operation will no longer be needed. The vital areas may be reduced as fewer buildings, equipment and systems need to be protected, which means access controls, surveillance and so on can be reduced. And also, decommissioning will probably require more workers than operation would, although this might not be the case at all times. From a security point of view, this might require more personnel or additional access points. Changing operating require changed security measures, to ensure that the required security level will be maintained while at the same time work proceeds efficiently. Once all of the fuel is removed from the plant, radiological release risk is much lower. The lower risk requires a lower level of security measures. Even during the removal of nuclear material and contaminated equipment from nuclear facilities, lower level of security measures should meet regulatory requirements based on a graded approach. Therefore, this study intends to examine the responsibilities and obligations of regulatory authorities, regulator, and nuclear operators in terms of protection after permanent shutdown and decommissioning.

The IAEA states that in the event of sabotage, nuclear material and equipment in quantities that can cause high radiological consequences (HRC), as well as the minimum systems and devices necessary to prevent HRC, must be located within one or more vital areas. Accordingly, in Article 2 of the ACT ON PHYSICAL PROTECTION AND RADIOLOGICAL EMERGENCY, the definition of the vital area is specified, and a nuclear facility operator submits a draft to the Nuclear Safety and Security Commission to establish vital areas and must obtain approval from Nuclear Safety and Security Commission. Since the spent fuel pool and new fuel storage area are areas where nuclear material is used and stored, they can be candidates for vital areas as direct targets of sabotage. The spent fuel pool is a wet spent fuel storage facility currently operated by most power plants in Korea to cool and store spent nuclear fuel. Considering the HRC against sabotage, it is necessary to review whether sepnt fuel pool needs to establish a vital area. In addition, depending on the status of plant operation during the spent fuel management cycle, the operation status of safety systems to mitigate accidents and power system change, so vital areas in fuel handling building (including spent fuel pool) also need to be adjusted flexibly. This study compares the results of the review on whether the essential consideration factors are reflected in the identification of essential safety systems and devices to minimize HRC caused by sabotage in the spent fuel storage system with the procedure for identifying the vital area in nuclear power plants. It was reviewed from the following viewpoints: Necessity to identify necessary devices to minimize the radiation effects against sabotage on the spent fuel pool, Review of necessary elements when identifying vital areas to minimize the radiation effects of spent fuel pool against sabotage, Necessity to adjust vital areas according to the spent fuel management cycle. The main assumptions used in the analysis of the vital area of the power plant need to be equally reflected when identifying vital areas in spent fuel pool. And, the results of this study are for the purpose of minimizing the radiological consequences against sabotage on the spent fuel storage system including the spent fuel pool and used to establish regulatory standards in the spent fuel storage stage.