Detectors utilized for nuclear material safeguards have been using scintillation detectors which are inexpensive and highly portable, and electrically cooled germanium detectors which are expensive but have excellent energy resolution. However, recently IAEA, the only international inspectorate of nuclear material safeguards for the globe, have replaced the existing scintillation detector and electrically cooled germanium detector with a CdZnTe detector owing to the improved performance of room-temperature semiconductors significantly. In this paper, we will examine the spectrum features of the CdZnTe detector such as spectrum shape, energy resolution, and efficiency in the energy region of interest, which are the important characteristics for measuring Uranium enrichment. For this purpose, it would be conducted to compare its spectrum features using CdZnTe, NaI, HPGe detectors. The main energies of interest include 185.7 keV and 1,001 keV, which are the decay energies of uranium 235 and uranium 238. The results of this study will provide a better understanding of the spectral features of various detectors used in uranium enrichment analysis, and are expected to be used as basic data for future related software development.

Nuclear safety, security, and safeguards (nuclear 3S) are essential components for establishing robust nuclear environments. Nuclear safety is to protect public and environments from radioactive contamination, which can be caused in accidents. Nuclear security is to protect nuclear facilities from terrorism or sabotage, which related to physical a ttacks or insider threats. And nuclear safeguards is to protect nuclear materials from extortion by a state with a purpose of weaponizing activities. When a new nuclear facility is introduced, it is possible to save abundant amount of resources by considering nuclear 3S in an early stage (design phases). Initially, the international atomic energy agency (IAEA) recommended safeguards-by-design (SBD) approach. The concept of SBD gradually expands to nuclear 3S-by-design (3SBD). Though there are differences in purpose and target subject, each nuclear ‘S’ is closely related with others. When introducing a certain technology or equipment in order to enhance one ‘S’, another ‘S’ also get affected. The effect can be synergies or conflicts. For instance, confidential information in nuclear security is required for a safeguards activity. On the contrary, inspection equipment for safeguards can be used for security. Pyroprocessing is a technology for managing used nuclear fuels. As pyroprocessing is a backend fuel cycle technology, a sensitive nuclear technology, safeguards has taken a large portion of nuclear 3S research in an effort to achieve international credibility and nuclear transparency. As mentioned, there are both synergies and conflicts in integrating nuclear 3S. In this study, we investigate potential challenges in applying nuclear 3S integration to pyroprocessing by addressing synergies and conflicts. This approach will suggest required supplementary methods to build the reliable pyroprocessing environment.

During PIV (Physical Inventory Verification), the IAEA has been inspecting the CANDU-Type spent fuels using an optical fiber-based scintillation detector. KINAC has developed a new verification instrument to deal with problems of the existing one such as low sensitivity, heavy and large dimension, and inconvenience-in-use. Our previous studies focused on how to develop the new instrument and had not included its performance tests. Field tests were carried out recently at Wolsung unit 4 to evaluate performance of the existing and new instruments. The objective of this paper is to discuss background noise produced in the optical fiber signal cable itself. The verification equipment for the CANDU-type Heavy Water Reactor spent fuels uses a scintillation detector to bond a scintillation material to the end of an optical signal cable. At this time, the radiation signal obtained by a data acquisition system is the signal generated from the scintillator (p-terphenyl organic scintillator) and the optical signal cable ; The signal produced in the optical cable itself is background noise to degrade the spent fuel verification equipment. To characterize the background radiation noise, the spent fuel bundles at Wolsung Unit 4 were measured using the optical fiber cable without the radiation scintillator. This signal is generated by reaction of the optical cable and the radiation emitted from the spent fuel. From experimental results, it was observed that the background noise signal of the optical cable increased as the optical cable went down in the downward direction, because the cable length irradiated by the radiation increased with the optical cable area in the spent fuel storage pool. Difference in the background noise signal was dependent on the location of the vertical direction and the signal of the new optical cable was up to about 5 times higher than that of the existing cable. While, the new cable has the cross-section area about 3.2 times larger than the old cable. Our past studies showed that total signal amplitude – sum of signals generated from the scintillator and optical fiber - of the new verification instrument was at least about 15 times greater than that of the existing one. Considering the total signal and background noise signal, from this measured results, it was confirmed that the scintillator characteristics – in particular, light output and decay time – has a dominant impact on the signal sensitivity of the newly developed instrument. More details will be discussed at the conference.

The Republic of Korea (ROK), as a member state of the IAEA, is operating the State’s System of Accounting for and Control (SSAC) and conducting independent national inspections. Furthermore, an evaluation methodology for the material unaccounted for (MUF) is being developed in ROK to enhance capabilities of national inspection. Generally, physical and chemical changes of nuclear material are unavoidable due to the operating system and structure of facilities, an accumulation of material unaccounted for (MUF) has been issued. IAEA developed statistical MUF evaluation method that can be applied to all facilities around the world and it mainly focuses on the diversion detection of nuclear materials in facilities. However, in terms of the national safeguard inspection, an evaluation of accountancy in facilities is additionally needed. Therefore, in this research, a new approach to MUF evaluation is suggested, based on the Guide to the Expression of Uncertainty in Measurement (GUM) that an evaluation of measurement uncertainty factors is straightforward. A hypothetical list of inventory items (LII) which has 6,118 items at the beginning and end of the material balance period, along with 360 inflow and outflow nuclear material items at a virtual fuel fabrication plant was employed for both the conventional IAEA MUF evaluation method and the proposed GUM-based method. To calculate the measurement uncertainty, it was assumed that an electronic balance, gravimetry, and a thermal ionization mass spectrometer were used for a measurement of the mass, concentration, and enrichment of 235U, respectively. Additionally, it was considered that independent and correlated uncertainty factors were defined as random factors and systematic factors for the ease of uncertainty propagation by the GUM. The total MUF uncertainties of IAEA (σMUF) and GUM (uMUF) method were 37.951 and 36.692 kg, respectively, under the aforementioned assumptions. The difference is low, it was demonstrated that the GUM method is applicable to the MUF evaluation. The IAEA method demonstrated its applicability to all nuclear facilities, but its calculated errors exhibited low traceability due to its simplification. In contrast, the calculated uncertainty based on the GUM method exhibited high reliability and traceability, as it allows for individual management of measurement uncertainty based on the facility’s accounting information. Consequently, the application of the GUM approach could offer more benefits than the conventional IAEA method in cases of national safeguard inspections where factor analysis is required for MUF assessment.

Nuclear fusion energy is considered as a future energy source due to its higher power density and no emission of greenhouse gas. Therefore, various researches on nuclear fusion is being conducted. One of the key materials for the nuclear fusion research is tritium because the D-T reaction is the main reaction in the nuclear fusion system. However, that tritium can also be used for non-peaceful purposes such as hydrogen bombs. Therefore, it is necessary to establish the safeguards system for tritium. In that regards, this study analyzed the possibility of applying safeguards to tritium. To achieve this objective, the tritium production capacity through the light water reactor was analyzed. Tritium Production Burnable Absorber Rod (TPBAR) was modeled through the MCNP code, and tritium production was analyzed. The TPBAR is composed of a cylindrical tube with a double coating of aluminum and zirconium, filled with a sintered lithium aluminate (LiAlO2) pellet to prevent the release of tritium. Tritium is produced by the reaction of Li-6 in the TPBAR with neutrons, and it is extracted and stored at the Tritium Extraction Facility (TEF). As a result, the tritium production increased as the burnup and Li-6 mass increased. In addition, when the tritium produced in this way was transferred to TEF and extracted through the process, the application of safeguards measures was analyzed. To this end, various safeguards measures were devised, such as setting an Material Balance Area (MBA) for TEF and analyzing Material Balance Period (MBP). As there is no designated Significant Quantity (SQ) for tritium, cases were classified based on the type and form of nuclear weapons to estimate the Sigma MUF (Material Unaccounted For) of the TEF. Finally, the comprehensive application of safeguards to tritium was discussed. This research is expected to contribute to the establishment of IAEA safeguards standards related to tritium by applying the findings to actual facilities.

Milling facilities, which belong to the front end of the nuclear fuel cycle, are essential steps for utilizing uranium in nuclear power generation. These milling facilities currently provide the International Atomic Energy Agency (IAEA) with the location and annual production capacity of the facility through the Additional Protocol (AP, INFCIRC/540) and grant IAEA inspectors on-site sampling authority to apply safeguards to the facility. However, since milling facilities process a large amount of nuclear material and the product uranium ore concentrate (UOC) is bulk material, the absence of accounting for the facility could pose a potential risk of nuclear proliferation. Therefore, this study proposes technical approach that can be utilized for safeguards in milling facilities. Since the half-life of uranium isotopes is much longer than that of its daughter, they reach the secular equilibrium condition. However, after milling process, the fresh tailing showed the break of that secular equilibrium. As time goes on, they newly reach another secular equilibrium condition. Based on this observation, this study discussed the feasibility of the ratio method in safeguards purpose. The scenario applied in this study was 1% of uranium mill tailing. It was observed that the U-238/Th-234 and U- 238/Pa-234m ratios in fresh milling tails varied as a function of time after discharging, particularly during the first one year. This change can be worked as a significant signature in terms of safeguards. In conclusion, the ratio method in mill tails could be applicable for safeguards of nuclear milling facility.

Korea Institute of Nuclear Non-proliferation and Control (KINAC) Safeguards division and Export control division operate regulation management system each other according to their work scope and characteristics. Korea Safeguards Information System (KSIS) of Safeguards division handles information for nuclear material accounting and control. Especially, accounting and declaration reports submitted to International Atomic Energy Agency (IAEA) are important information in this system. And Nuclear Import and Export Control System (NEPS) of Export control division deals with import and export information of nuclear materials and nuclear weapon trigger list items. Establishing and operating the integrated database as sharing information between KSIS and NEPS derive merits as follows. First, the full cycle of nuclear material transfer records can be managed by collecting information on the nuclear materials from import to export or disposal. In addition, regulatory body can verify inconsistency between transfer records and account records in date, location, element, mass etc. Especially, small quantity nuclear materials are major loop hole in nuclear material accountancy system. The accumulated material transfer data will give an evidence to catch loss nuclear material. Second, sharing the information on nuclear fuel cycle related research and development activities in both divisions can utilize the information to outreach on facility subject to nuclear technology transfer for Nuclear Suppliers Group (NSG) and additional protocol declaration for Safeguards Agreement with IAEA. Third, regulatory body is easily able to manage entire import and IAEA report procedure for items subject to the Nuclear Cooperation Agreement (NCA). In present, KINAC regulation on NCA is divided to Export control and Safeguards. Export control division conducts classification imported items subject to NCA and acquires prior consent or notifies to other country. And Safeguards division report inventory list for each NCA country to the ROK government once a year. Imported NCA inventory list will be generated automatically by merging database. Then, it can be easily verified without any additional process by both divisions.

Dry storage cask facilities are considered for temporary storage of spent nuclear fuels before their final disposal. According to relevant domestic laws and regulations, the integrity and gross defects of the PWR spent fuel must be inspected before they are transferred to the dry cask from a wet storage pool of a nuclear power plant. To meet nuclear safeguards requirements for a spent fuel transportation, the KINAC has been working to develop a simple and convenient Non-destructive Testing (NDT) equipment to verify the integrity and gross defects of the spent fuel assembly. This study was conducted in two processes. The first stage is to review the current NDT techniques conducted in the nuclear fuel manufacturing process. During the manufacturing process, the Ultrasonic testing (UT) and Eddy Current Testing (ECT) technique are used for detecting the cracks or foreign materials in a cladding of a fresh fuel. During an over-haul period after an end of one fuel cycle, the sipping test of the spent fuel is performed for detecting the failed fuel assemblies. If it is determined through the sipping test whether any fuel assembly contains a failed fuel rod, the failed fuel rod of lots of fuel rods in the assembly is found out using the UT instrument. The ECT is used for detecting the internal defects and oxide layer thickness of a fuel cladding. Because the UT and ECT are the wellknown technique and has already been employing for the spent fuel inspection, we adopted the UT and ECT technique for development of a new instrument for nuclear safeguards verification. The second stage is to design the UT and ECT equipment in consideration of nuclear safeguards activities in the spent fuel pool. For nuclear safeguards inspection, irradiated fuel or non-fuel items are distinguished. Thus, verification equipment newly designed using the UT and ECT should detect not only a failed rod, but also a false tube, or a false rod, or a different material from a cladding. New probe and signal processing methods are developed to achieve these goals. The design of UT and ECT probes are preferentially carried out according to technical requirements – the probe thickness including a damper material should be less than 1.0 mm - and the study on analyzing signal distortion caused from material difference will be conducted for development of the safeguards inspection equipment. Detailed results of our study will be discussed in this conference.