• Nuclear Engineering and Technology
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• 제34권4호
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• pp.382-395
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• 2002

An experimental study on transient critical heat flux (CHF) under flow coastdown has been performed for the water flow in a non-uniformly heated vertical annulus under low flow and a wide range of pressure conditions. The objectives of this study are to systematically investigate the effect of the flow transient on the CHF and to compare the transient CHF with steady-state CHF The transient CHF experiments have been performed for three kinds of flow transient modes based on the coastdown data of a nuclear power plant reactor coolant pump. At the same inlet subcooling, system pressure and heat flux, the effect of the initial mass flux on the critical mass flux can be negligible. However, the effect of the initial mass flux on the time-to- CHF becomes large as the heat flux decreases. The critical mass flux has the largest value for slow flow reduction rate. There is a pressure effect on the ratio of the transient CHF data to steady-state CHF data. Except under low system pressure conditions, the flow transient CHF was revealed to be conservative compared with the steady-state CHF data. Bowling CHF correlation and thermal hydraulic system code MARS show promising results for the prediction of CHF occurrence .

• Nuclear Engineering and Technology
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• 제54권1호
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• pp.310-317
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• 2022

The mass attenuation coefficient is the primary physical parameter to model narrow beam gamma-ray attenuation. A new machine learning based approach is proposed to model gamma-ray shielding behavior of composites alternative to theoretical calculations. Two fuzzy logic algorithms and a neural network algorithm were trained and tested with different mixture ratios of vanadium slag/epoxy resin/antimony in the 0.05 MeV-2 MeV energy range. Two of the algorithms showed excellent agreement with testing data after optimizing adjustable parameters, with root mean squared error (RMSE) values down to 0.0001. Those results are remarkable because mass attenuation coefficients are often presented with four significant figures. Different training data sizes were tried to determine the least number of data points required to train sufficient models. Data set size more than 1000 is seen to be required to model in above 0.05 MeV energy. Below this energy, more data points with finer energy resolution might be required. Neuro-fuzzy models were three times faster to train than neural network models, while neural network models depicted low RMSE. Fuzzy logic algorithms are overlooked in complex function approximation, yet grid partitioned fuzzy algorithms showed excellent calculation efficiency and good convergence in predicting mass attenuation coefficient.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.579-587
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• 2017

Spaceborne cryocoolers produce undesirable micro-vibration disturbances during their on-orbit operation, which are a primary source of image-quality degradation for high-resolution observation satellites. Therefore, to comply with the strict mission requirement of high-quality image acquisition, micro-vibration disturbances induced by cooler operation have always been subjected to an isolation objective. However, in this study, we focused on the applicability of energy harvesting technology to generate electrical energy from micro-vibration energy of the cooler and investigated the feasibility of utilizing harvested energy as a power source to operate low-power-consumption devices such as micro-electromechanical system (MEMS) devices. A tuned mass damper (TMD)-type electromagnetic energy harvester combined with a conventional passive vibration isolator was proposed to achieve this objective. The system performs the dual functions of electrical energy generation and micro-vibration isolation. The effectiveness of the strategy was evaluated through numerical simulations.

• Nuclear Engineering and Technology
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• 제45권3호
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• pp.415-420
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• 2013

A determination method for $^{237}Np$ in spent nuclear fuel samples was developed using an isotope dilution method with $^{239}Np$ as a spike. In this method, inductively coupled plasma mass spectrometry (ICP-MS) was taken for the $^{237}Np$ instead of the previously used alpha spectrometry. $^{237}Np$ and $^{239}Np$ were measured by ICP-MS and gamma spectrometry, respectively. The recovery yield of $^{237}Np$ in synthetic samples was $95.9{\pm}9.7$% (1S, n=4). The $^{237}Np$ contents in the spent fuel samples were 0.15, 0.25, and $1.06{\mu}g/mgU$ and these values were compared with those from ORIGEN-2 code. A fairly good agreement between the measurements (m) and calculations (c) was obtained, giving ratios (m/c) of 0.93, 1.12 and 1.25 for the three PWR spent fuel samples with burnups of 16.7, 19.0, and 55.9 GWd/MtU, respectively.

• 신재생에너지
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• 제18권2호
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• pp.82-89
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• 2022

In this study, the exergy characteristics were analyzed, according to the mass flow rate of the propane working fluid and the pressure change in the turbine inlet, for the efficient recovery of cold energy and exhaust heat by the waste energy recovery system applied to the LNG FSRU regasification process. When the turbine inlet pressure and mass flow rate of the Primary Rankine Cycle were kept constant, the exergy efficiency and the net power increased. This occurred as the turbine inlet pressure and the mass flow rate of the working fluid increased in the Secondary Rankine Cycle, respectively, and the maximum values were confirmed. In this regard, the fluctuations in the exergy rate flowing into and out of the system and the exergy rate destroyed by pumps, evaporators, turbines, and LNG heat exchangers (condensers) were examined in detail.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.701-708
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• 2022

The mass attenuation coefficients (μ_m) of polyethylene glycol (PEG) of different molecular weights (1000-200,000) were measured using single-beam photon transmission. The X-ray fluorescent (XRF) photons from Zinc (Zn), Zirconium (Zr), Molybdenum (Mo), Silver (Ag) and Cadmium (Cd) targets were used to determine the attenuation of gamma radiation of energy range between 8.67 and 23.19 keV in PEG samples. The results were compared to theoretical values using XCOM and Monte Carlo simulation using Geant4 toolkit which was developed to validate the experiment at those certain energies. The mass attenuation coefficients were then used to compute the effective atomic numbers, electron density and half value layers for the studied samples. The outcomes showed good agreement between experimental and simulated results with those calculated theoretically by XCOM within 5% deviation. The PEG 1000 sample showed slightly higher μ_m value compared with the other samples. The dependence of the photon energy and PEG composition on the values of μ_m and HVL were investigated and discussed. In addition, the values of Z_eff and N_eff for all PEG samples behaved similarly in the given photon energy range, and they decreased as the photon energy increased.

• 한국소음진동공학회논문집
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• 제25권9호
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• pp.637-643
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• 2015

In recent years, pattern recognition methods have been widely used by many researchers for fault diagnoses of mechanical systems. The soundness of a mechanical system can be checked by analyzing the variation of the system vibration characteristic along with a pattern recognition method. Recently, the hidden Markov model has been widely used as a pattern recognition method in various fields. In this paper, the hidden Markov model is employed for the fault diagnosis of the mass unbalance of a rotating system. Mass unbalance is one of the critical faults in the rotating system. A procedure to identity the location and size of the mass unbalance is proposed and the accuracy of the procedure is validated through experiment.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2011년도 춘계학술발표대회 논문집
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• pp.195-198
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• 2011

Liquid desiccant material, such as lithium chloride (LiCl) or halide slits are usually used on air conditioning application for controlling the humidity of high Outdoor Air (OA). Solar energy is usually used to heat the liquid in regeneration process of those desiccant. The mass transfer it self is driven by the temperature different between the liquid desiccant and the input air. This experiment study is analyzing the characteristic of the aqueous LiCl-air temperature different in variance specific gravity, especially in range of temperature different using the solar energy as the heat generator. The experiment has done by variating the concentration of the LiCl with specific gravity 1.210 and 1.150. For the comparison the pure water is also used. The result show that the mass transfer rate is increased in every variation as the increases of the temperature different, and the weeker aqueous solution of the LiCl the highest mass transfer coefficient.

• Nuclear Engineering and Technology
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• 제47권7호
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• pp.907-914
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• 2015

The energetic steam explosion caused by contact between the high temperature molten core and water is one of the phenomena that may threaten the integrity of the containment vessel during severe accidents of light water reactors (LWRs). We examined the dependence of steam explosion loads in a typical reactor cavity geometry on selected model parameters and initial/boundary conditions by using a steam explosion simulation code, JASMINE, developed at Japan Atomic Energy Agency (JAEA). Among the parameters, we put an emphasis on the water pool depth that has significance in terms of accident mitigation strategies including cavity flooding. The results showed a strong correlation between the load and the premixed mass, defined as the mass of the molten material in low void zones (void fraction < 0.75). The jet diameter and velocity that comprise the flow rate were the primary factors to determine the premixed mass and the load. The water pool depth also showed a significant impact. The energy conversion ratio based on the enthalpy in the premixed mass was in a narrow range ~4%. Based on this observation, we proposed a simplified method for evaluation of the steam explosion load. The results showed fair agreement with JASMINE.

• 한국방사선학회논문지
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• 제10권8호
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• pp.591-596
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• 2016

본 연구의 목적은 실험으로 6 MV X-선 빔의 등가에너지를 결정하는 데 있다. 6 MV X-선 빔에 대한 납의 반가층은 전리함을 사용하여 측정하였다. 선감쇠계수는 측정된 반가층을 사용하여 계산하였다. 그리고 질량감쇠계수는 납의 밀도로 선감쇠계수를 나누어 얻었다. 얻어진 질량감쇠계수의 등가에너지는 미국표준기술연구소에서 주어진 납의 광자에너지 대 질량감쇠계수 자료를 사용하여 결정하였다. 그 결과로서, 6 MV X-선 빔에 대한 등가에너지는 1.61 MeV로 결정되었다. 이 등가에너지는 Reft가 보고한 것 보다 약 30% 낮게 결정되었다. 그 원인은 납 감쇠기 사이의 공기공동의 존재에 기인한 것으로 추정된다.