[en] This paper first explores safeguards approaches that have been applied to dry storage in the Republic of Korea, Kazakhstan, and Ukraine. The study then reviews legislations in Nuclear Safety Act of the Republic of Korea and federal regulations in the United States in comparison with the IAEA safeguards manual. We then suggest a proposal on amendments for the effective implementation of safeguards for the interim dry storage system designed for Pressurized Water Reactors (PWR) spent fuel assemblies. The initiative on interim dry storage for PWR spent nuclear fuels in the Republic of Korea has raised concerns regarding the implementation of safeguards at dry storage facilities. The study analyzed and compared provisions that provide legal grounds for safeguards in the Republic of Korea and the United Sates in comparison with criteria in the IAEA safeguards manual. We then derived a suggestion on amendments to the current Nuclear Safety Act. To the extent of the comprehensive safeguards agreement, new provisions should embrace and yield effective safeguards implementations by the IAEA as well as domestic safeguards activities on difficult-to-access items. Along with this approach, the comparison analysis between the provisions in Nuclear Safety Act and 10CFRs and the IAEA criteria suggested amendments to the existing Nuclear Safety Act. We concluded that it is required to include paragraphs defining the terminology, ‘Difficult-to-Access’, and incorporating difficult-to-access items in the scope of reporting and inspection procedures. In addition, provisions embodying special requirements for the items designated difficult to access were suggested for a legal preparedness to the dry storage facilities planned to be installed in the Republic of Korea.

[en] Korea Institute of Nuclear Nonproliferation and Control (KINAC) have developed Quad-CZT ^1st and Quad-CZT ²ⁿd system for uranium enrichment verifycation. Developed Quad-CZT systems consist of detector and laptop computer, which are connected by USB cable. Paradoxically, one of the most serious drawback of the condition is that operation time is limited to battery capacity of laptop computer and distance is limited to length of the cable. Moreover, it causes the long preparation time for set-up the detection. As these reasons, Quad-CZT ^3rd system is being developed to simplify equipment for improving portability. This paper will give an account of characteristic of Quad-CZT ^3rd system Quad-CZT ^3rd system is developed in order to overcome an inconvenience for USB connection of already developed Quad-CZT ^1st system and Quad-CZT ²ⁿd system. Quad-CZT ^3rd system is operated under wireless network for uranium enrichment verification. Availability will be increased because constraints of UBS connection are resolved. Finally, a variety of experiments will be conducted to improve performance of a Quad-CZT ^3rd system at field or NDA laboratory. Additionally, Development of Quad-CZT ^3rd system would be expected to utilize safeguard inspections on nuclear facility because of convenience and accessibility. Moreover, it will be looking forward to inspection equipment of IAEA.

[en] IAEA required each State to develop a verification method of nuclear material presented in the State's accounts. Depending on the safeguards objectives, Korea Institute of Nuclear Nonproliferation and Control (KINAC) currently focuses on how to effectively and quickly analyze various samples such as concrete, graphite and aluminum via DA (Destructive Analysis) techniques. Alpha spectrometry or ICP-MS are typically applied to assess uranium particle concentration but they suffer from long measurement time, high cost and etc. UV/Vis spectrophotometry is a comparatively easy substitute method and generally used in chemistry since it is featured by its good accuracy and lower cost compared with other methods. Therefore, with the purpose of safeguards, UV/Vis spectrophotometry was applied to determine uranium concentration in a concrete sample, produced through nuclear fuel fabrication. This study was conducted how to quickly decide uranium concentration based on the color and spectrum characteristics using UV/Vis spectrophotometry.

[en] The master plan for spent nuclear fuel (SNF) management in Korea recently adopted by Korean atomic energy promotion council. According to the master plan, the detailed practical and R and D strategies for SNF transferring, storage and disposal should be determined in the near future. Besides, it is also necessary to make plan how to secure SNF at each step in terms of nuclear safeguards, safety, security and nonproliferation. Several nondestructive analysis (NDA) techniques have been studied for assuring the safety of SNF in PWR methods. Obviously, gamma-ray is most dominant radiation emitted by SNF so several gamma-ray measurement methods have been developed and applied for the purpose of SNF monitoring. Those methods, however, suffer from a lack of nuclear data and interfering background radiation. To date, several neutron measurement methods have been developed as a solution to the problem of gamma-ray methods. Korea Institute of Nuclear Nonproliferation and Control (KINAC) currently develops a new novel technique of fast neutron detection for spent fuel monitoring at dry spent fuel storage facilities. As the first step, a computational program has been developed in order to evaluate neutron flux on the surface of PWR dry storage cask and study for some potential sabotage events. Typically, neutron flux on the surface of dry storage cask can be evaluated via two steps. The source term, based on burn-up rate of SNF, its cooling time and others related to operation condition at nuclear power plants, can be firstly defined by ORIGEN code. The surface flux can be then evaluated via MCNP code. These two separated steps are complicated and time consuming so KINAC developed a new algorithm and user-interface, coupled ORIGEN and MCNP. (authors)

[en] it can provide effective information on the presence of high-Z materials, has a high enough energy to deeply penetrate large amounts of shielding, and does not lead to any health risks and danger above background. We developed a 2-D muon detector and designed a muon tomography system employing four detector modules. Two top and two bottom detectors are, respectively, employed to record the incident and the scattered muon trajectories. The detector module for the muon tomography system consists of a plastic scintillator, wavelength-shifting (WLS) fiber arrays placed orthogonally on the top and the bottom of the scintillator, and a position-sensitive photomultiplier (PSPMT). The WLS fiber arrays absorb light photons emitted by the plastic scintillator and re-emit green lights guided to the PSPMT. The light distribution among the WLS fiber arrays determines the position of the muon interaction; consequently, 3-D tomographic images can be obtained by extracting the crossing points of the individual muon trajectories by using a point-of-closest-approach algorithm. The goal of this study is to optimize the design parameters of a muon tomography system by using the Geant4 code and to experimentally evaluate the performance of the prototype detector. Images obtained by the prototype detector with a 420-nm laser light source showed good agreement with the simulation results. This indicates that the proposed detector is feasible for use in a muon tomography system and can be used to verify the Z-discrimination capability of the muon tomography system.

[en] L-edge densitometry (LED) which is specially called X-ray Absorption Spectrometry (XAS) for uranium xray analysis is a technique of determination of uranium concentration as a continuous x-ray energy beams transmit a uranium liquid sample for safeguard. Compared to K-edge densitometer, since relatively lower energy of uranium L series energy than K series energy, L-edge densitometer does not require a liquid nitride cooling system. In this study, the simulation of uranium L-edge densitometer is performed using Monte Carlo method. Ledge spectrum, such as spectrum jumps, can be confirmed by the simulation. In further study, improvement of counting efficiency through collimation of x-ray, and shielding will be considered for detailed design of L-edge densitometer

[en] Visual inspection makes easier to ensure the integrity and safety of spent nuclear fuel (SNF) than any classical techniques. Various classical techniques have been applied but there are no reliable methods to qualitatively and quantitatively verify spent fuel in dry storage. Thus, the present authors have developed the prototype safeguards apparatus for dry storage employing the array of He-4 gas scintillation detectors (S670E, Arktis Radiation Detectors Ltd., Switzerland), newly designed to simultaneously measure thermal and fast neutrons without any moderators. The S670E detector has a cylindrical shape with a diameter of 52 mm and active length of 600 mm (total length: 875 mm). The detector is filled by He-4 gas with an approximate pressure of 180 bar for fast neutron detection, and its inner wall is coated by Li-6 for thermal neutron detection. The scintillation lights generated via Li-6 nuclear reaction and elastic scattering are collected by 24 SiPMs linearly paired at the center of the detector. The detector delivers a TTL (Transistor-Transistor Logic) output for pulse readout and UART (Universal Asynchronous Receiver Transmitter) for device control. In order to assess feasibility of the apparatus, an experimental system has been designed, built, and optimized via computational studies. Cf-252 neutron sources and linearly arrayed detectors, working as a single detector, were occupied for this study due to the difficulties in working with SNF. The laboratory scale cask (diameter: 0.67 m, height: 1.5 m), minimized by a factor of 10 compared to the actual thickness of a commercial TN-32 cask, was also manufactured. The detector array was designed to rotate the lab-scale cask and obtain 36 image profiles at every 10 degrees. All profiles were aligned in single frame image called a sinogram, and the cross-sectional image was then fabricated by the inverse radon transform algorithm. These experiments have been repeated with different configurations and numbers of sources. Some gamma-ray sources were also measured with neutron sources in order to distinguish between neutron and gamma-ray pulses. Basically, a He-4 detector is designed to run on Linux OS so it is difficult to directly apply to Windows-based equipment widely used in S. Korea. Therefore, a new data acquisition board working on Windows OS was designed and built. The board mainly consists of FPGA (Field Programmable Gate Array) and SoC (System on Chip) for TTL pulse readout, sorting measured data, and transferring data to a user interface. In conclusion, the tomographic system at lab-scale has shown considerable potential to detect a partial or gross defect of encapsulated assemblies in dry storage. Next steps of this study will be to 1) repeatedly carry out experiments to demonstrate scientific reliability and validity, and 2) numerically integrate signals with weight factors to enhance the image quality since the suggested system based on passive interrogation method requires longer measurement time. Finally, the system will apply to a commercial dry storage phased out soon in S. Korea. (authors)

[en] The delayed neutron nuclear data are limited by its short lifetime, limited yield fraction, difficulty to obtain a well-defined sample, an inefficient (uncharacterized) experimental system, and numerical instabilities of fitting methods. The uncertainties on the relative abundances of the longer-lived delayed neutron groups are up to 13% for thermal fissions of "2"3"5U and 16% for fast fissions of "2"3"8U. To evaluate more accurate delayed neutron nuclear data, a novel approach to experimentally measure the relative uncertainties on the delayed neutron group abundances has been proposed by Jordan and Perret. This approach combines delayed gamma and delayed neutron fission rate measurement techniques; with two independent estimates of the same fission rate, higher uncertainty delayed neutron parameters can be linked to lower uncertainty delayed gamma parameters. The present authors have designed, optimized, and built an experimental apparatus capable of producing high accuracy measurements for delayed gamma-rays and neutrons, with the goal of implementing the above approach. Finally, sensitivity studies of the parameters that have non-negligible contributions to the overall uncertainty were carried out. With regards to the designed setup and the combined technique, the relative uncertainty of the longest-lived delayed neutron group is calculated. The calculation shows that the uncertainty of the longest-lived delayed neutron group of "2"3"8U can be reduced by a factor of two to 8.81%. (author)

[en] Alpha spectroscopy is widely used for detecting undeclared nuclear facilities, activities, and materials. Due to the heavy equipment required to carry out this technique, its applications is limited. With the goal of quickly and efficiently responding to undeclared nuclear facilities, activities, and materials, the present authors have designed and built a portable α-particle spectrometer. This study was conducted in order to develop a new portable α-particle spectrometer with the purpose of detecting undeclared nuclear facilities, activities, and materials on site quickly and efficiently. All heavy and large components, which are typically required for a laboratory such as a αparticle spectrometry system, were minimized and placed in a small container with a weight of 14 kg and a size of 30 cm x 30 cm x 30 cm. In the feasibility study, the calculated enrichment values of "2"3"5U obtained from the portable α-particle spectrometer were 1.868 % and 3.083 %, similar to the results from a commercial spectrometry system used in laboratories, 2.049 % and 3.253 %. These differences were possibly caused by different channel setups for each system

[en] This analysis can be used to identify the undeclared nuclear activities of North Korea. The international community has developed a method of collecting and analyzing uranium particles within a limited time in the field to determine whether or not undeclared nuclear activities have taken place. This study shows the U source using CeF_3 coprecipitation has no significant difference. In addition, this CeF_3 coprecipitation method is simple and time saving. It is expected to be useful for rapid on-site detection of undeclared uranium enrichment activities