• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.803-811
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• 2024

Nuclear accidents such as Fukushima Daiichi have highlighted the potential of passive safety systems to replace or complement active safety systems as part of the overall prevention and/or mitigation strategies. In addition, passive systems are key features of Small Modular Reactors (SMRs), for which they are becoming almost unavoidable and are part of the basic design of many reactors available in today's nuclear market. Nevertheless, their potential to significantly increase the safety of nuclear power plants still needs to be strengthened, in particular the ability of computer codes to determine their performance and reliability in industrial applications and support the safety demonstration. The PASTELS project (September 2020-February 2024), funded by the European Commission "Euratom H2020" programme, is devoted to the study of passive systems relying on natural circulation. The project focuses on two types, namely the SAfety COndenser (SACO) for the evacuation of the core residual power and the Containment Wall Condenser (CWC) for the reduction of heat and pressure in the containment vessel in case of accident. A specific design for each of these systems is being investigated in the project. Firstly, a straight vertical pool type of SACO has been implemented on the Framatome's PKL loop at Erlangen. It represents a tube bundle type heat exchanger that transfers heat from the secondary circuit to the water pool in which it is immersed by condensing the vapour generated in the steam generator. Secondly, the project relies on the CWC installed on the PASI test loop at LUT University in Finland. This facility reproduces the thermal-hydraulic behaviour of a Passive Containment Cooling System (PCCS) mainly composed of a CWC, a heat exchanger in the containment vessel connected to a water tank at atmospheric pressure outside the vessel which represents the ultimate heat sink. Several activities are carried out within the framework of the project. Different tests are conducted on these integral test facilities to produce new and relevant experimental data allowing to better characterize the physical behaviours and the performances of these systems for various thermo-hydraulic conditions. These test programmes are simulated by different codes acting at different scales, mainly system and CFD codes. New "system/CFD" coupling approaches are also considered to evaluate their potential to benefit both from the accuracy of CFD in regions where local 3D effects are dominant and system codes whose computational speed, robustness and general level of physical validation are particularly appreciated in industrial studies. In parallel, the project includes the study of single and two-phase natural circulation loops through a bibliographical study and the simulations of the PERSEO and HERO-2 experimental facilities. After a synthetic presentation of the project and its objectives, this article provides the reader with findings related to the physical analysis of the test results obtained on the PKL and PASI installations as well an overall evaluation of the capability of the different numerical tools to simulate passive systems.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4447-4464
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• 2023

This paper focuses on the development of a new computational model of the CNESTEN's TRIGA Mark II research reactor using the 3D continuous energy Monte-Carlo code TRIPOLI-4 (T4). This new model was developed to assess neutronic simulations and determine quantities of interest such as kinetic parameters of the reactor, control rods worth, power peaking factors and neutron flux distributions. This model is also a key tool used to accurately design new experiments in the TRIGA reactor, to analyze these experiments and to carry out sensitivity and uncertainty studies. The geometry and materials data, as part of the MCNP reference model, were used to build the T4 model. In this regard, the differences between the two models are mainly due to mathematical approaches of both codes. Indeed, the study presented in this article is divided into two parts: the first part deals with the development and the validation of the T4 model. The results obtained with the T4 model were compared to the existing MCNP reference model and to the experimental results from the Final Safety Analysis Report (FSAR). Different core configurations were investigated via simulations to test the computational model reliability in predicting the physical parameters of the reactor. As a fairly good agreement among the results was deduced, it seems reasonable to assume that the T4 model can accurately reproduce the MCNP calculated values. The second part of this study is devoted to the sensitivity and uncertainty (S/U) studies that were carried out to quantify the nuclear data uncertainty in the multiplication factor k_eff. For that purpose, the T4 model was used to calculate the sensitivity profiles of the k_eff to the nuclear data. The integrated-sensitivities were compared to the results obtained from the previous works that were carried out with MCNP and SCALE-6.2 simulation tools and differences of less than 5% were obtained for most of these quantities except for the C-graphite sensitivities. Moreover, the nuclear data uncertainties in the k_eff were derived using the COMAC-V2.1 covariance matrices library and the calculated sensitivities. The results have shown that the total nuclear data uncertainty in the k_eff is around 585 pcm using the COMAC-V2.1. This study also demonstrates that the contribution of zirconium isotopes to the nuclear data uncertainty in the k_eff is not negligible and should be taken into account when performing S/U analysis.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.34 no.5
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• pp.973-980
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• 2024

Fuzzing is an automated testing technique that generates a lot of testcases and monitors for exceptions to test a program. Recently, fuzzing research using machine learning has been actively proposed to solve various problems in the fuzzing process, but a comprehensive evaluation of fuzzing research using machine learning is lacking. In this paper, we analyze recent research that applies machine learning to scheduling techniques for fuzzing, categorizing them into reinforcement learning-based and supervised learning-based fuzzers. We evaluated the coverage performance of the analyzed machine learning-based fuzzers against real-world programs with four different file formats and bug detection performance against the LAVA-M dataset. The results showed that AFL-HIER, which applied seed clustering and seed scheduling with reinforcement learning outperformed in coverage and bug detection. In the case of supervised learning, it showed high coverage on tcpdumps with high code complexity, and its superior bug detection performance when applied to hybrid fuzzing. This research shows that performance of machine learning-based fuzzer is better when both machine learning and additional fuzzing techniques are used to optimize the fuzzing process. Future research is needed on practical and robust machine learning-based fuzzing techniques that can be effectively applied to programs that handle various input formats.

• Journal of the Korean Society of Food Science and Nutrition
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• v.37 no.12
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• pp.1640-1646
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• 2008

In the current food sanitation regulation, food additives are under controlled by the Food Code. The naturally derived preservatives such as benzoic acid and propionic acid can be naturally carried over or produced as metabolites during manufacturing process such as fermentation. To monitor naturally formed benzoic acid and propionic acid levels, a total of 145 samples were classified into berries (prune, cranberry), functional foods (propolis liquid, ginseng product), vinegars (vinegar-based drink, vinegar beverage, vinegar), and salted and pickled products (olive, pickled cucumber, salted/pickled product) and analyzed by HPLC-PDA and GC-FID. From the results, benzoic acid and propionic acid were each detected and identified in 144 samples and 64 samples respectively. The amount of benzoic acid ranged from $4.1{\sim}478.4\;ppm$ in cranberry, from $49.7{\sim}491$ in propolis liquid, and from $2.5{\sim}10.2\;ppm$ in ginseng, and other tested samples contained very small quantity. Also, the amount of propionic acid ranged from $179.8{\sim}951.9\;ppm$ (av. 553.6 ppm) in vinegar (persimmon vinegar 100%), which was the highest level among fermented foods, from $13.7{\sim}247.0$ ppm in propolis liquid, from $2.0{\sim}180.7\;ppm$ in vinegar-based drink, and from $1.6{\sim}76.6\;ppm$ in olive. Vinegar beverage and pickled cucumber each showed 24 and 18 ppm of propionic acid; in contrast, propionic acid was not detected in prune, cranberry, ginseng, and picked/salted products.

• Progress in Medical Physics
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• v.27 no.1
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• pp.31-36
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• 2016

The paper discusses radiation dose of dual energy CT on which copper modulation layer, is mounted in order to improve diagnostic performance of the dual energy CT. The radiation dose is estimated using MCNPX and its results are compared with that of the conventional dual energy CT system. CT X-ray spectra of 80 and 120 kVp, which are usually used for thorax, abdominal, head, and neck CT scans, were generated by the SPEC78 code and were used for the source specification 'SDEF' card for MCNPX dose modeling. The copper modulation layer was located 20 cm away from a source covering half of the X-ray window. The radiation dose was measured as changing its thickness from 0.5 to 2.0 mm at intervals of 0.5 mm. Since the MCNPX tally provides only normalized values to a single particle, the dose conversion coefficients of F6 tally for the modulation layer-based dual energy CBCT should be calculated for matching the modeling results into the actual dose. The dose conversion coefficient is $7.2*10^4cGy/output$ that is obtained from dose calibration curve between F6 tally and experimental results in which GAFCHORMIC EBT3 films were exposed by an already known source. Consequently, the dose of the modulation layer-based dual energy cone beam CT is 33~40% less than that of the single energy CT system. On the basis of the results, it is considered that scattered dose produced by the copper modulation layer is very small. It shows that the modulation layer-based dual energy CBCT system can effectively reduce radiation dose, which is the major disadvantage of established dual energy CT.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.7
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• pp.1-8
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• 2017

As the IT environment becomes more sophisticated, various threats and their associated serious risks are increasing. Threats such as DDoS attacks, malware, worms, and APT attacks can be a very serious risk to enterprises and must be efficiently managed in a timely manner. Therefore, the government has designated the important system as the main information communication infrastructure in consideration of the impact on the national security and the economic society according to the 'Information and Communication Infrastructure Protection Act', which, in particular, protects the main information communication infrastructure from cyber infringement. In addition, it conducts management supervision such as analysis and evaluation of vulnerability, establishment of protection measures, implementation of protection measures, and distribution of technology guides. Even now, security consulting is proceeding on the basis of 'Guidance for Evaluation of Technical Vulnerability Analysis of Major IT Infrastructure Facilities'. There are neglected inspection items in the applied items, and the vulnerability of APT attack, malicious code, and risk are present issues that are neglected. In order to eliminate the actual security risk, the security manager has arranged the inspection and ordered the special company. In other words, it is difficult to check against current hacking or vulnerability through current system vulnerability checking method. In this paper, we propose an efficient method for extracting diagnostic data regarding the necessity of upgrading system vulnerability check, a check item that does not reflect recent trends, a technical check case for latest intrusion technique, a related study on security threats and requirements. Based on this, we investigate the security vulnerability management system and vulnerability list of domestic and foreign countries, propose effective security vulnerability management system, and propose further study to improve overseas vulnerability diagnosis items so that they can be related to domestic vulnerability items.

• The Korean Journal of Pesticide Science
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• v.21 no.1
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• pp.49-61
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• 2017

The study was conducted for safety evaluation of 208 kinds of residue pesticides on 200 dried agricultural products, which are distributed in Gwangju. The method of monitoring was the second of Multi Class Pesticide Multi-residue Methods in Korean Food Code, and GC-ECD, GC-NPD, GC-MSD, and LC-MS/MS were used as evaluation equipment to analyze. The residue level in pesticides were 15.5% (31 of 200 samples) and 4 samples exceeded MRLs. 4.5 mg/kg of pyraclostrobin (MRL; 3.0 mg/kg) was detected in red pepper, 1.49 mg/kg of chlorpyrifos (MRL; 0.13 mg/kg) in daikon leaves, 38.26 mg/kg of pyridalyl (MRL; 0.25 mg/kg) in pepper leaves, 0.98 mg/kg of chlorpyrifos (MRL; 0.05 mg/kg), respectively. Pesticides were found on the 15 samples among the 21 samples of red pepper which is a fruit vegetable, and this resulted in high detection rate of 71%. In addition, pesticides were detected on chwinamul, shitake, siler divaricata, daikon leaves and others within MRLs. The frequent detected kinds of pesticides were insecticide (47.6%), fungicide (33.3%), acaricide (14.3%), nematicide (4.8%) in the order named, and pesticides were methoxyfenozide > pyraclostrobin > azoxystrobin, chlorantraniprole > novaluron, trifloxystrobin in frequent order.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.2
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• pp.211-222
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• 2011

In this paper a structural analysis of the PWR(pressurized water reactor) canister with 102cm diameter is carried out to evaluate the structural safety of the canister for the impact force occurring at the moment of collision with the ground in the falling plumb down accident from the carriage vehicle which may happen during the canister handling at the spent nuclear fuel disposal repository. For this, a rigid body dynamic analysis of the canister is executed to compute the impact force using the commercial CAE system, RecurDyn, and a nonlinear structural analysis is performed to compute stresses and deformations occurring inside the canister for this computed impact force using the commercial FEM code, NISA. From these analysis results, the structural safety of the canister is evaluated for the falling plumb down accident from the carriage vehicle due to the inattention during the canister handling at the repository. The rigid body dynamic analysis performed assuming the canister as a rigid body shows that the canister falls plumb down to the ground in two types. And also it shows that early collision impact force is the biggest one and following impact forces decrease gradually. The height of the carriage vehicle in the repository is assumed as 5m in order to obtain the stable structural safety evaluation result. The nonlinear structural analysis of the canister is executed for the biggest early impact force. The structural analysis result of the canister shows that the structural safety of the PWR canister is not secured for the falling plumb down accident from the moving carriage vehicle because the maximum stresses occurring in the cast iron insert of canister are bigger than the yield stress of the cast iron.

• Journal of Food Hygiene and Safety
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• v.34 no.4
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• pp.367-373
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• 2019

In order to evaluate the microbiological safety of ice cream products, the total viable bacterial counts were measured in 6 kinds of ice pops, 5 kinds of non-milk fat ice cream, and 5 kinds of milk fat ice cream, sold in local markets. In addition, E. coli, S. aureus, B. cereus, and L. monocytogenes were artificially inoculated in three types of ice cream products and stored at $-5^{\circ}C$, $-10^{\circ}C$, and $-18^{\circ}C$, respectively, and after inoculation, viable cells were measured periodically. As a result of the total viable count, about 1~2 log CFU/mL was detected in 16 kinds of ice cream products. As a result of inoculation with microorganisms at various temperatures, the number of viable cells decreased as the storage period became longer, and the higher the storage temperature, the faster the microorganisms died. Especially, the microorganisms were killed faster in the ice pop products than in the other ice cream products, and the microorganisms were killed relatively slower in the milk ice cream. L. monocytogenes and S. aureus were relatively stable in frozen conditions compared to other microorganisms. The microbial contamination of commercial ice cream was lower than the allowable standard of the Korean Food Code. Microorganisms did not proliferate when the microorganism was inoculated at freezing temperature. Therefore, it is expected that the microbiological safety of frozen foods will be ensured if the sanitary control and disinfection of raw materials are thoroughly carried out during the production of frozen confections and the temperature control during distribution and storage is well maintained.

• Journal of the Korean Society of Radiology
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• v.16 no.4
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• pp.373-379
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• 2022

The radiation source used for non-destructive testing have permeability and cause a scattered radiation through collisions of surrounding materials, which causes changes in the surrounding spatial dose. Therefore, this study attempted to evaluate and analyze the distribution of spatial dose by source in the working environment during the non-destructive test using monte carlo simulation. In this study, Using FLUKA, a simulation code, simulates ⁶⁰Co, ¹⁹²Ir, and ⁷⁵Se source used in non-destructive testing, The reliability of the source term was secured by comparing the calculated dose rate with the data of the Health and Physics Association. After that, a non-destructive test in the radiation safety facility(RT-room) was designed to evaluate the spatial dose according to the distance from the source. As a result of the spatial dose evaluation, ⁷⁵Se source showed the lowest dose distribution in the frontal position and ⁶⁰Co source showed a dose rate of about 15 times higher than that of ⁷⁵Se and about 2 times higher than that of ¹⁹²Ir. In addition, the spatial dose according to the distance tends to decrease according to the distance inverse square law as the distance from the source increases. Exceptionally, ⁶⁰Co, ¹⁹²Ir, and ⁷⁵Se sources confirmed a slight increase within 2 m of position. Based on the results of this study, it is believed that it will be used as supplementary data for safety management of workers in radiation safety facilities during non-destructive testing using radioactive isotopes.