• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
• /
• pp.420-423
• /
• 2002

In recent years, there has been keen interest in developing f1at panel detectors for all modalities of radiology, including gerneral radiology, fluoroscopy(angiography and cardiology), electronic portal imaging, and mammography. In this paper, we report the new hybrid x-ray detector consisted of CsI(Tl) photoemission layer and a-Se photoconductor layer to resolve conventional x-ray detector such as the direct detector using a-Se and the indirect detector using CsI(Tl)/a-Si. To design the structure of CsI(Tl)/a-Se detector, the penetrated energy spectrum and absorption fraction was estimated using MCNP 4C code. Experimental results showed that the absorption fraction of $500{\mu}m-Se$ film and $150{\mu}m-CsI\left(Tl \right)/a-Se\left( 30{\mu}m \right)$ film is 70% at 70 kVp. The absorption energy is 90% at $350{\mu}m-CsI(Tl)$.

• Current Optics and Photonics
• /
• 제5권2호
• /
• pp.114-120
• /
• 2021

Free-space optical (FSO) communication is considered to be a potential solution to congestion in the radio-frequency spectrum and last-mile-access bottleneck issues in future cellular communication networks, such as 5G and beyond. However, FSO link performance may degrade significantly due to irradiance fluctuations and random temporal fluctuations from atmospheric turbulence. Therefore, in this work the main objective is to reduce the effect of the atmospheric turbulence by considering a multihop FSO communication system with amplify-and-forward relaying supported by a radio-frequency (RF) link, which form a hybrid FSO/RF communication system. The FSO link is assumed to follow the gamma-gamma fading model, which represents strong turbulence. Also, the RF link is modeled by a Rayleigh distribution. The performance of the considered system, in terms of the outage probability and average bit-error rate (BER), is investigated and analyzed under various weather conditions and pointing errors. Furthermore, the effect of the number of employed relay nodes on the performance of the system is investigated. The results indicate that the considered system reduces outage probability and average BER significantly, especially for low channel quality. Finally, the closed-form expressions derived in this work are compared to the results of Monte Carlo simulations, for verification.

• Nuclear Engineering and Technology
• /
• 제51권2호
• /
• pp.369-376
• /
• 2019

A complete solution for a soluble-boron-free (SBF) small modular reactor (SMR) is pursued with a new burnable absorber concept, namely centrally-shielded burnable absorber (CSBA). Neutronic flexibility of the CSBA design has been discussed with fuel assembly (FA) analyses. Major design parameters and goals of the SBF SMR are discussed in view of the reactor core design and three CSBA designs are introduced to achieve both a very low burnup reactivity swing (BRS) and minimal residual reactivity of the CSBA. It is demonstrated that the core achieves a long cycle length (~37 months) and high burnup (~30 GWd/tU), while the BRS is only about 1100 pcm and the radial power distribution is rather flat. This research also introduces a supplementary reactivity control mechanism using stainless steel as mechanical shim (MS) rod to obtain the criticality during normal operation. A further analysis is performed to investigate the local power peaking of the CSBA-loaded FA at MS-rodded condition. Moreover, a simple $B_4C$-based control rod arrangement is proposed to assure a sufficient shutdown margin even at the cold-zero-power condition. All calculations in this neutronic-thermal hydraulic coupled investigation of the 3D SBF SMR core are completed by a two-step Monte Carlo-diffusion hybrid methodology.

• Nuclear Engineering and Technology
• /
• 제54권11호
• /
• pp.4226-4230
• /
• 2022

The Korea Atomic Energy Research Institute (KAERI) has designed a Hybrid-Low Power Research Reactor (H-LPRR) which can be used for critical assembly and conventional research reactor as well. It is an open tank-in-pool type research reactor (Thermal Power: 50 kW_th) of which the most important applications are Neutron Activation Analysis (NAA), Radioisotope (RI) production, education and training. There are eight irradiation holes on the edge of the reactor core: IR (6 holes for RI production) and NA (2 holes for NAA) holes. In order to quantify the elemental concentration in target samples through the Instrumental Neutron Activation Analysis (INAA), it is necessary to measure neutron spectrum parameters such as thermal neutron flux, the deviation from the ideal 1/E epithermal neutron flux distribution (α), and the thermal-to-epithermal neutron flux ratio (f) for the irradiation holes. In this study, the MCNP6.1 code and FORTRAN 90 language are applied to determine the parameters for the two irradiation holes (NA-SW and NA-NW) in H-LPRR, and in particular its α and f parameters are compared to values of other research reactors. The results confirmed that the neutron irradiation holes in H-LPRR are designed to be sufficiently applied to neutron activation analysis, and its performance is comparable to that of foreign research reactors including the TRIGA MARK II.

• Nuclear Engineering and Technology
• /
• 제55권5호
• /
• pp.1838-1854
• /
• 2023

This paper presents a hybrid algorithm to solve the multi-objective path planning (MOPP) problem for mobile robots in a static nuclear accident environment. The proposed algorithm mimics a real nuclear accident site by modeling the environment with a two-layer cost grid map based on geometric modeling and Monte Carlo calculations. The proposed algorithm consists of two steps. The first step optimizes a path by the hybridization of improved ant colony optimization algorithm-modified A^* (IACO-A^*) that minimizes path length, cumulative radiation dose and energy consumption. The second module is the high radiation dose rate avoidance strategy integrated with the IACO-A^* algorithm, which will work when the mobile robots sense the lethal radiation dose rate, avoiding radioactive sources with high dose levels. Simulations have been performed under environments of different complexity to evaluate the efficiency of the proposed algorithm, and the results show that IACO-A^* has better path quality than ACO and IACO. In addition, a study comparing the proposed IACO-A^* algorithm and recent path planning (PP) methods in three scenarios has been performed. The simulation results show that the proposed IACO-A^* IACO-A^* algorithm is obviously superior in terms of stability and minimization the total cost of MOPP.

• Structural Engineering and Mechanics
• /
• 제89권3호
• /
• pp.309-321
• /
• 2024

In this paper, the effect of semi-rigid connections on the stability bearing capacity of cross-bracings in steel tubular transmission towers is investigated. Herein, a prediction method based on the hybrid model which is a combination of particle swarm optimization (PSO) and backpropagation neural network (BPNN) is proposed to accurately predict the stability bearing capacity of cross-bracings with semi-rigid connections and to efficiently conduct its probabilistic assessment. Firstly, the establishment of the finite element (FE) model of cross-bracings with semi-rigid connections is developed on the basis of the development of the mechanical model. Then, a dataset of 7425 samples generated by the FE model is used to train and test the PSO-BPNN model, and the accuracy of the proposed method is evaluated. Finally, the probabilistic assessment for the stability bearing capacity of cross-bracings with semi-rigid connections is conducted based on the proposed method and the Monte Carlo simulation, in which the geometric and material properties including the outer diameter and thickness of cross-sections and the yield strength of steel are considered as random variables. The results indicate that the proposed method based on the PSO-BPNN model has high accuracy in predicting the stability bearing capacity of cross-bracings with semi-rigid connections. Meanwhile, the semi-rigid connections could enhance the stability bearing capacity of cross-bracings and the reliability of cross-bracings would significantly increase after considering semi-rigid connections.

• Nuclear Engineering and Technology
• /
• 제55권12호
• /
• pp.4491-4503
• /
• 2023

This study aimed to verify and validate the transient simulation capability of the hybrid code system RAST-F for fast reactor analysis. For this purpose, control rod (CR) drop experiments involving eight separate CRs and six CR groups in the China Experimental Fast Reactor (CEFR) start-up tests were utilized to simulate the CR drop transient. The RAST-F numerical solution, including the neutron population, time-dependent reactivity, and CR worth, was compared against the measurement values obtained from two out-of-core detectors. Moreover, the time-dependent reactivity and CR worth from RAST-F were verified against the results obtained by the Monte Carlo code Serpent using continuous energy nuclear data. A code-to-code comparison between Serpent and RAST-F showed good agreement in terms of time-dependent reactivity and CR worth. The discrepancy was less than 160 pcm for reactivity and less than 110 pcm for CR worth. RAST-F solution was almost identical to the measurement data in terms of neutron population and reactivity. All the calculated CR worth results agreed with experimental results within two standard deviations of experimental uncertainty for all CRs and CR groups. This work demonstrates that the RAST-F code system can be a potential tool for analyzing time-dependent phenomena in fast reactors.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2006년도 추계학술대회 논문집 광주전남지부
• /
• pp.96-100
• /
• 2006

A pulsed laser ablation deposition (PLAD) technique is an excellent method for the fabrication of amorphous carbon (a-C) films. This paper was focused on the understanding and analysis of the motion of carbon atom (C) and carbon ion ($C^+$) particles in laser ablation assisted by Ar plasmas. The simulation has carried out under the pressure P=10~100 mTorr of Ar plasmas. Two-dimensional hybrid model consisting of fluid and Monte-Carlo models was developed and three kinds of the ablated particles which are C, $C^+$ and electron were considered in the calculation of particle method. The motions of energetic $C^+$ and C deposited upon the substrate were investigated and compared.

• Steel and Composite Structures
• /
• 제41권6호
• /
• pp.831-850
• /
• 2021

Surface subsidence caused by mining subsidence has an impact on neighboring structures and utilities. In other words, subsurface voids created by mining or tunneling activities induce soil movement, exposing buildings to physical and/or functional destruction. Soil-structure is evaluated employing probability distribution laws to account for their uncertainty and complexity to estimate structural vulnerability. In this study, to investigate the displacement field and surface settlement profile caused by mining subsidence, on the basis of a Winklersoil model, analytical equations for the moment-rotation response ofsoil during mining induced ground movements are developed. To define the full static moment-rotation response, an equation for the uplift-yield state is constructed and integrated with equations for the uplift- and yield-only conditions. The constructed model's findings reveal that the inverse of the factor of safety (x) has a considerable influence on the moment-rotation curve. The maximal moment-rotation response of the footing is defined by X = 0:6. Despite the use of Winkler model, the computed moment-rotation response results derived from the literature were analyzed through the ELM-SVM hybrid of Extreme Learning Machine (ELM) and Support Vector Machine (SVM). Also, Monte Carlo simulations are used to apply continuous random parameters to assess the transmission of ground motions to structures. Following the findings of RMSE and R2, the results show that the choice of probabilistic laws of input parameters has a substantial impact on the outcome of analysis performed.

• 한국방사선학회논문지
• /
• 제8권6호
• /
• pp.333-338
• /
• 2014

최근 의료 분야에서의 불필요한 피폭을 체계적으로 관리해야 한다는 사회적 요구 증가와 더불어 차폐의 중요성이 대두되고 있는 실정이다. 하지만 현재 상용화된 제품은 다양한 의료방사선 분야보다 세분되어 있지 않다. 이에 본 연구에서는 최적화된 차폐재의 구조를 몬테카를로 시뮬레이션을 활용하여 제시하고자 하였다. 모의 추정 결과, 유방촬영 에너지(30 kVp) 스펙트럼에 대하여 단일 차폐재의 경우 $30{\mu}mPb$, 2 mmAl에서 90% 이상의 차폐율을 확인하였고, 이중차폐 구조에서는 0.03 mmPb와 1 mmAl의 설계 시 효율적인 것으로 판단되었다. 또한, 일반촬영 에너지(80 kVp) 스펙트럼에 대해서는 $340{\mu}mPb$, 30 mmAl에서 90% 이상의 차폐율을 확인하였으며, 이중차폐 구조에서는 0.3 mmPb와 1 mmAl의 설계가 유용할 것으로 사료된다. 이러한 결과는 향후 피폭저감을 위한 맞춤형 상용화 제품 개발에 대한 기초자료로 활용될 수 있을 것으로 기대된다.