• Nuclear Engineering and Technology
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• v.37 no.3
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• pp.207-220
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• 2005

Nuclear power plants (NPP) are complex socio-technological systems that rely on the success of both hardware and human components. Empirical studies of plant operating experience show that human errors are important contributors to accidents and incidents, and that organizational factors play an important role in creating contexts for human errors. Current probabilistic safety assessments (PSA) do not explicitly model the systematic contribution of organizational factors to safety. As some countries, like the United States, are moving towards increased use of risk information in the regulation and operation of nuclear facilities, PSA quality has been identified as an area for improvement. The modeling of human errors, and underlying organizational weaknesses at the root of these errors, are important sources of uncertainty in existing PSAs and areas of on-going research. This paper presents a review of research into the following questions: Is there evidence that organizational factors are important to NPP safety? How do organizations contribute to safety in NPP operations? And how can these organizational contributions be captured more explicitly in PSA? We present a few past incidents that illustrate the potential safety implications of organizational deficiencies, some mechanisms by which organizational factors contribute to NPP risk, and some of the methods proposed in the literature for performing root-cause analyses and including organizational factors in PSA.

• Nuclear Engineering and Technology
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• v.51 no.2
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• pp.510-517
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• 2019

Increasing proliferation resistance of plutonium by way of increased $^{238}Pu$ content is of interest to the nuclear nonproliferation and international safeguards community. Considering the high alpha decay heat of $^{238}Pu$, increasing the isotopic fraction leads to a noticeably higher amount of heat generation within the plutonium. High heat generation is especially unattractive in the scenario of weaponization. Upon weaponization of the plutonium, the plutonium may generate enough heat to elevate the temperature in the high explosives to above its self-explosion temperature, rendering the weapon useless. In addition, elevated temperatures will cause thermal expansion in the components of a nuclear explosive device that may produce thermal stresses high enough to produce failure in the materials, reducing the effectiveness of the weapon. Understanding the technical limit of $^{238}Pu$ required to reduce the possibility of weaponization is key to reducing the current limit on safeguarded plutonium (greater than 80 at. % $^{238}Pu$). The plutonium vector evaluated in this study was found by simulating public information on Lightbridge's fuel design for pressurized water reactors. This study explores the temperature profile and maximum stress within a simple (first generation design) hypothetical nuclear explosive device of four unique scenarios over time. Analyzing the transient development of both the temperature profile and maximum stress not only establishes a technical limit on the $^{238}Pu$ content, but also establishes a time limit for which each scenario would be useable.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.198-206
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• 2019

A new methodology to analyze the nuclear material accountability for pyroprocessing system is developed. The $Pu-to-^{244}Cm$ ratio quantification is one of the methods for Pu accountancy in pyroprocessing. However, an uncertainty in the $Pu-to-^{244}Cm$ ratio due to the non-uniform composition in used fuel assemblies can affect the accountancy of Pu. A random variable, LOPu, is developed to analyze the probability of detection for Pu diversion of hypothetical scenarios at a pyroprocessing facility considering the uncertainty in $Pu-to-^{244}Cm$ ratio estimation. The analysis is carried out by the hypothesis testing and the event tree method. The probability of detection for diversion of 8 kg Pu is found to be less than 95% if a large size granule consisting of small size particles gets sampled for measurements. To increase the probability of detection more than 95%, first, a new Material Balance Area (MBA) structure consisting of more number of Key Measurement Points (KMPs) is designed. This multiple KMP-measurement for the MBA shows the probability of detection for 8 kg Pu diversion is greater than 96%. Increasing the granule sample number from one to ten also shows the probability of detection is greater than 95% in the most ranges for granule and powder sizes.

• Nuclear Engineering and Technology
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• v.52 no.7
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• pp.1452-1461
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• 2020

A triple bubbler sensor was tested in LiCl-KCl molten salt from 450 to 525 ℃ in a transparent furnace to validate thermal-expansion corrections and provide additional molten salt data sets for calibration and validation of the sensor. In addition to these tests, a model was identified and further developed to accurately determine the density, surface tension, and depth from the measured bubble pressures. A unique feature of the model is that calibration constants can be estimated using independent depth measurements, which allow calibration and validation of the sensor in an electrorefiner where the salt density and surface tension are largely unknown. This model and approach were tested using the current and previous triple bubbler data sets, and results indicate that accuracies are as high as 0.03%, 4.6%, and 0.15% for density, surface tension, and depth, respectively.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.356-361
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• 1997

DUPIC 공정의 핵연료에 대핀 핵물질 보장조치(safeguards)를 이행하여 핵투명성(nuclear transparency)을 검증하기 위한 중성자측정장치를 개발하였다. 본 장치를 사용한 보장조치 원리 및 기술적 사항, 장치 설계 개념 등에 관해서는 본 논문의 전편$^{[1]}$ 에서 기술하였고 여기서는 제작된 측정장계에 대한 성능시험 내용을 중심으로 나타내었다. 즉, 일반시설(cold lab.)내에서 실시한 성능시험 결과로부터 장치의 각 부분별 기능이 정상적으로 작동되고 있음을 확인할 수 있었으며 이것은 현재 후속과정으로 핫셀(hot cell)내에서 사용후핵연료를 이용하여 수행중인 성능시험 결과를 분석하는 기본자료로 활용될 것이다. 본 장치 개발을 통하여 확보한 중성자측정 기술은 앞으로 고준위감마선방출 핵물질을 사용하는 후행핵연료주기 시설에 대한 핵물질 통제 및 계량관리에 필요한 보장조치 기술로 활용될 수있을 것으로 기대된다..

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2016.05a
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• pp.25-26
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• 2016

In this paper, the major changes of the national inspection in respect of the KAERI nuclear facilities were summarized. The frequency of the national inspection was decreased since the amendment of the Notification of the NSSC on the national inspection. But the national inspection broadened its scope and its implementation procedures and criteria were not clear. So, it is necessary to establish and enhance the national inspection system including the implementing guides and criteria. In addition, the internal regulation of the nuclear material accountancy for the nuclear facilities should be approved from the NSSC and observed by the KAERI in accordance with the national law. As the Notification of the NSSC on the national inspection was amended in Sep. 2014, it need to be revised to reflect the detail accountancy procedures and the preparation of the national inspection. So, KAERI will revise it to meet the international and national requirements as well as to implement the safeguards effectively at facility level.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4327-4331
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• 2011

A new method in thermal ionization mass spectrometry (TIMS) was developed to correct peak tailing backgrounds in the isotope ratio measurements of uranium in ultra trace levels for higher accuracy. Two different uranium standard reference materials (U005 and U030) were used to construct databases of signal intensities at mass 234 u and mass 236 u, which correspond to the two uranium minor isotopes, and signal intensity of $^{238}U$. Correlations between peak tailing backgrounds and $^{238}U$ were obtained by least-squares regression on calculated backgrounds at mass 234 u and mass 236 u with respect to the signal intensity of $^{238}U$ followed by separation of the peak tails of the two major isotopes of uranium ($^{235}U$ and $^{238}U$), which enables us to obtain a master equation for peak tailing background correction on all kinds of samples. Verification of the correction method was carried out using U010 and IRMM-040a.

• Journal of Radiation Industry
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• v.18 no.1
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• pp.9-14
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• 2024

In order to thoroughly verify the denuclearization of the Korean Peninsula, it is urgent to develop technology capabilities to monitor, detect, collect, analyze, interpret, and evaluate nuclear activities using nuclear materials and secure nuclear transparency. The IAEA is actively using seal technology to maximize the efficiency of safety measures, and currently uses metal cap, paper, COBRA, and EOSS as seal devices. Unlike facilities that comply with safety measures requirements, such as domestic nuclear facilities, facilities subject to denuclearization are likely to have various risk environments that make it difficult to apply safety measures, and there is a high possibility that continuity of knowledge (COK) such as damage, malfunction, and power loss will not be maintained. This study aims to develop a real-time active seal device that can be applied in such special situations to enable immediate response in the event of a similar situation. To this end, the main functions of the real-time seal device were derived and applied, and a commercialized seal device and operation software. The real-time seal technology developed through this study can be applied to all nuclear facilities in South Korea, especially used as storage equipment for dry cask storage facilities of heavy water reactor's after fuel, and it is believed that unnecessary radiation exposure by inspectors can be minimized.

• Nuclear Engineering and Technology
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• v.55 no.11
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• pp.3925-3934
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• 2023

The importance of fast neutron detection for nuclear safeguards purposes has increased due to its potential advantages such as reasonable cost and higher precision for larger sample masses of nuclear materials. Pulse-shape discrimination (PSD) is inevitably used to discriminate neutron- and gamma-ray- induced signals from organic scintillators of very high gamma sensitivity. The light output (LO) threshold corresponding to several MeV of recoiled proton energy could be necessary to achieve fine PSD performance. However, this leads to neutron count losses and possible distortion of results obtained by neutron multiplicity counting (NMC)-based nuclear material accountancy (NMA). Moreover, conventional PSD techniques are not effective for counting of neutrons in a high-gamma-ray environment, even under a sufficiently high LO threshold. In the present work, PSD performance (figure-of-merit, FOM) according to LO bands was confirmed using a conventional charge comparison method (CCM) and compared with results obtained by convolution neural network (CNN)-based PSD algorithms. Also, it was attempted, for the first time ever, to reject fake neutron signals from distorted PSD regions where neutron-induced signals are normally detected. The overall results indicated that higher neutron detection efficiency with better accuracy could be achieved via CNN-based PSD algorithms.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.1006-1011
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• 1998

전면안전조치 협정국인 이라크의 비밀 핵무기 계발과 핵 개발 의혹국인 북한의 특별사찰 거부로 야기된 IAEA의 안전조치강화방안(Strengthened Safeguards System, SSS)은 기존의 IAEA 안전조치에 대한 효과성과 효율성을 제고하기 위하여 마련된 방안이다. 이 중 안전조치의 효과성은 핵물질의 전용 방지를 정확하고 빠르게 탐지하는데 있으며 이러한 안전조치의 효과성은 기술적인 방법과 정치적인 방법이 조화를 이루면서 획득될 수 있다. 기술적인 면에서는 정보제공과 접근확대에 대한 IAEA의 하부구조 개발이 순조롭게 진행됨으로써 효과성을 기대할 수 있다. 반면 정치적인 면에서의 효과성은 전면안전조치 협정국으로서 원자력에 대한 기술력을 확보한 국가의 조기참여예상으로 긍정적인 면이 있으나 이라크 및 북한, 그리고 부분 안전조치협정국의 참여 불투명은 SSS의 효과성을 단기적으로 떨어뜨리는 요인으로 작용할 것으로 딘인다. 따라서 IAEA는 상기불투명국의 SSS에의 참여를 유도하는 것이 안전조치의 효과성을 확보하기 위한 남은 과제라 할 수 있다.