• 한국수소및신에너지학회논문집
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• 제22권3호
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• pp.402-408
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• 2011

Organic Rankine cycles (ORC) can be used to produce power from heat at different temperature levels available as geothermal heat, as biogenic heat from biomass, as solar or as waste heat. In ORC working fluids with relatively low critical temperatures and pressures can be compressed directly to their supercritical pressures and heated before expansion so as to obtain a better thermal match with their heat sources. In this work thermal performance of ORC with and without an internal heat exchanger is comparatively investigated in the range of subcritical and transcritical cycles. R134a is considered as working fluid and special attention is paid to the effect of turbine inlet pressure on the characteristics of the system. Results show that operation with supercritical cycles can provide better performance than subcritical cycles and the internal heat exchanger can improve the thermal efficiency when the temperature of heat source becomes higher.

• 대한기계학회논문집B
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• 제41권11호
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• pp.699-707
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• 2017

본 연구에서는 아홉 종류의 작동유체를 고려하여 저온 열원으로 구동되는 아임계 및 초월임계 유기 랭킨 사이클의 열역학적 성능 특성을 비교 해석한다. 터빈입구압력, 열원온도 및 작동유체가 열교환기 내 온도분포와 핀치포인트, 작동유체의 유량, 시스템 출력 및 열효율 등 시스템의 성능에 미치는 영향을 분석한다. 해석 결과는 작동유체의 압력이 아임계 영역에서 초임계 영역으로 높아지면 열교환기에서 열원과 작동유체 사이의 온도 불균일 정도가 감소하면서 시스템 출력이나 열효율 등은 증가하나 시스템의 단위출력당 터빈 크기는 작아짐을 보여준다.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2004년도 Proceedings of the 4th Korea-China Joint Workshop on Nuclear Waste Management
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• pp.150-164
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• 2004

According to the Korean long-term plan for nuclear technology development, KAERI is conducting a few R&D projects related to the proliferation-resistant back-end fuel cycle. The R&D activities for the back-end fuel cycle are reviewed in this work, especially focusing on the study of the partitioning and transmutation(P&T) of long-lived radionuclides. The P&T study is currently being carried out in order to develop key technologies in the areas of partitioning and transmutation. The partitioning study is based on the development of pyroprocessing such as electrorefining and electrowinning because they can be adopted as proliferation-resistant technologies in the fuel cycle. In this study, various behaviors of the electrodeposition of uranium and rare earth elements in the LiCl-KCl electrorefining system have been examined through fundamental experimental work. As for the transmutation system, KAERI is studying the HYPER (HYbrid Power Extraction Reactor), a kind of subcritical reactor which will be connected with a proton accelerator. Up to now, a conceptual study has been carried out for the major elemental systems of the subcritical reactor such as core, transuranic fuel, long-lived fission product target, and the Pb-Bi cooling system, etc. In order to enhance the transmutation efficiency of the transuranic elements as well as to strengthen the reactor safety, the reactor core was optimized by determining its most suitable subcriticality, the ratio of height/diameter, and by introducing the concepts of optimum core configuration with a transuranic enrichment as well as a scattered reloading of the fuel assemblies.

• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1600-1609
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• 2017

The accelerator-driven subcritical system (ADS) is driven by a neutron source from spallation reactions introduced by the injected proton beam. Part of the neutron source has energy as high as a few hundred MeV to a few GeV. The effects of high-energy source neutrons ($E_n$ > 20 MeV) are usually approximated by energy cut-off treatment in practical core calculations, which can overestimate the predicted proton beam current in the ADS design. This article intends to quantize this effect and propose a way to solve this problem. To evaluate the effects of high-energy neutrons in the subcritical core, two models are established aiming to cover the features of current experimental facilities and industrial-scale ADS in the future. The results show that high-energy neutrons with $E_n$ > 20 MeV are of small fraction (2.6%) in the neutron source, but their contribution to the source efficiency is about 23% for the large scale ADS. Based on this, a neutron source efficiency correction factor is proposed. Tests show that the new correction method works well in the ADS calculation. This method can effectively improve the accuracy of the prediction of the proton beam current.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.304-317
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• 2016

An accelerator-driven system consists of a subcritical reactor and a controllable external neutron source. The reactor in an accelerator-driven system can sustain fission reactions in a subcritical state using an external neutron source, which is an intrinsic safety feature of the system. The system can provide efficient transmutations of nuclear wastes such as minor actinides and long-lived fission products and generate electricity. Recently at Kyoto University Research Reactor Institute (KURRI; Kyoto, Japan), a series of reactor physics experiments was conducted with the Kyoto University Critical Assembly and a Cockcrofte-Walton type accelerator, which generates the external neutron source by deuteriu-metritium reactions. In this paper, neutronic analyses of a series of experiments have been re-estimated by using the latest Monte Carlo code and nuclear data libraries. This feasibility study is presented through the comparison of Monte Carlo simulation results with measurements.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.360-367
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• 2016

A windowless spallation target can provide a neutron source and maintain neutron chain reaction for a subcritical reactor, and is a key component of China's nuclear waste transmutation of coupling accelerator and subcritical reactor. The main issue of the windowless target design is to form a stable and controllable free surface that can ensure that energy spectrum distribution is acquired for the neutron physical design when the high energy proton beam beats the lead-bismuth eutectic in the spallation target area. In this study, morphology and flow characteristics of the free surface of the windowless target were analyzed through the volume of fluid model using computational fluid dynamics simulation, and the results show that the outlet cross section size of the target is the key to form a stable and controllable free surface, as well as the outlet with an arc transition. The optimization parameter of the target design, in which the radius of outlet cross section is $60{\pm}1mm$, is verified to form a stable and controllable free surface and to reduce the formation of air bubbles. This work can function as a reference for carrying out engineering design of windowless target and for verification experiments.

• Nuclear Engineering and Technology
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• 제49권6호
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• pp.1301-1309
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• 2017

The extinction probability of a branching process (a neutron chain in a multiplying medium) is calculated for a system randomly varying in time. The evolution of the first two moments of such a process was calculated previously by the authors in a system randomly shifting between two states of different multiplication properties. The same model is used here for the investigation of the extinction probability. It is seen that the determination of the extinction probability is significantly more complicated than that of the moments, and it can only be achieved by pure numerical methods. The numerical results indicate that for systems fluctuating between two subcritical or two supercritical states, the extinction probability behaves as expected, but for systems fluctuating between a supercritical and a subcritical state, there is a crucial and unexpected deviation from the predicted behaviour. The results bear some significance not only for neutron chains in a multiplying medium, but also for the evolution of biological populations in a time-varying environment.

• 한국식품과학회지
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• 제47권6호
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• pp.772-778
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• 2015

최근 아임계수 가수분해는 전통적인 단백질 가수분해법의 대체방법으로서 관심을 받고 있으며, 고단백질원으로부터 아미노산을 회수하는데 효과적인 공정이 될 수 있을 것으로 기대되고 있다. 본 연구에서는 대표적인 식물성 단백질원인 분리대두단백질을 선택하여 대두단백질의 아임계수 가수분해에서 가장 중요한 인자인 대두단백질의 초기농도, 반응온도, 반응시간의 영향을 연구하여 대두단백질로부터 아미노산을 생산할 수 있는 조건을 최적화하고자 하였다. 대두단백질 수열분해액의 실온에서 pH는 $200^{\circ}C$에서 20분간 처리했을 때 pH는 7.3으로 중성이었으나 온도가 증가할수록 pH가 증가하여 $270^{\circ}C$에서 10.3으로 알카리성을 나타내었다. 반응온도 $220^{\circ}C$까지는 수열분해액은 분산상태를 이루었으나 $230^{\circ}C$ 이상에서는 분산상태가 파괴되고 단백질이 분리되어 하부에 침강층을 이루었으며 $240^{\circ}C$ 이상에서는 이 단백질층이 현저히 감소하였다. 반응온도는 $250^{\circ}C$, 반응시간 20분으로 고정한 조건에서 대두현탁액의 초기농도가 수열분해에 미치는 영향을 살펴본 결과 초기농도 10% (w/v)일 때 가수분해도 및 아미노산 수율이 각각 16.2% 및 22.3%로 가장 우수하였다. 또한 반응온도 $200-220^{\circ}C$ 범위에서는 가수분해도와 아미노산 수율은 서서히 증가하였으나 $230-250^{\circ}C$ 영역에서는 급격히 증가하였으며 $250^{\circ}C$ 이상에서는 다시 완만히 증가하는 경향을 보여 $250^{\circ}C$ 이상에서 아미노산 분해속도는 단백질 분해속도를 초과하였다. 표면반응분석법으로 예측한 결과 $268^{\circ}C$, 처리시간 35분에서 최적 아미노산 수율 43.5%를 얻을 수 있었다.

• Preventive Nutrition and Food Science
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• 제21권2호
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• pp.132-137
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• 2016

Enhanced production of individual phenolic compounds by subcritical water hydrolysis (SWH) of pumpkin leaves was investigated at various temperatures ranging from 100 to $220^{\circ}C$ at 20 min and at various reaction times ranging from 10 to 50 min at $160^{\circ}C$. Caffeic acid, p-coumaric acid, ferulic acid, and gentisic acid were the major phenolic compounds in the hydrolysate of pumpkin leaves. All phenolic compounds except gentisic acid showed the highest yield at $160^{\circ}C$, but gentisic acid showed the highest yield at $180^{\circ}C$. The cumulative amount of individual phenolic compounds gradually increased by 48.1, 52.2, and $78.4{\mu}g/g$ dry matter at $100^{\circ}C$, $120^{\circ}C$, and $140^{\circ}C$, respectively, and then greatly increased by $1,477.1{\mu}g/g$ dry matter at $160^{\circ}C$. The yields of caffeic acid and ferulic acid showed peaks at 20 min, while those of cinnamic acid, p-coumaric acid, p-hydroxybenzoic acid, and procatechuic acid showed peaks at 30 min. Antioxidant activities such as 2,2-diphenyl-1-picrylhydrazyl and ferric reducing antioxidant power values gradually increased with hydrolysis temperature and ranged from 6.77 to 12.42 mg ascorbic acid equivalents/g dry matter and from 4.25 to 8.92 mmol $Fe^{2+}$/100 g dry matter, respectively. Color $L^*$ and $b^*$ values gradually decreased as hydrolysis temperature increased from $100^{\circ}C$ to $140^{\circ}C$. At high temperatures ($160^{\circ}C$ to $220^{\circ}C$), L* and b* values decreased suddenly. The $a^*$ value peaked at $160^{\circ}C$ and then decreased as temperature increased from $160^{\circ}C$ to $220^{\circ}C$. These results suggest that SWH of pumpkin leaves was strongly influenced by hydrolysis temperature and may enhanced the production of phenolic compounds and antioxidant activities.

• 산업식품공학
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• 제22권4호
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• pp.304-308
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• 2018

건강 지향적인 사회 추세의 영향으로 건강 기능 식품의 관심과 개발이 증가되고 있다. 계피는 기능적 특성으로 인해 한약뿐만 아니라 식품 성분으로도 사용되고 있어서 본 연구에서는 추출용매와 추출방법을 달리하여 육계피 추출액의 향기 성분과 항산화활성도를 조사하였다. 육계피 추출물의 향기 성분인 coumarin, cinnamic acid, cinnamaldehyde, cinnamyl alcohol의 함량을 조사하였다. 에탄올 70%의 추출물에서 courmarin, cinnamic acid 그리고 cinnamylaldehyde의 함량은 증류수를 이용한 열수추출물과 아임계추출물에 비하여 높게 나타났다. 증류수를 이용한 아임계추출물의 courmarin, cinnamic acid, 그리고 cinnamaldehyde 함량은 열수추출물보다 높게 나타났지만, cinnamyl alcohol은 반대로 낮게 나타났다. DPPH 분석을 통한 항산화활성도 측정에서 DPPH scavenging activity는 추출물의 농도가 증가할수록 증가하였고, 70% 에탄올 추출물의 항산화활성도가 가장 크게 나타났다. FRAP 분석을 통한 항산화활성도 측정에서 70% 에탄올 추출물의 ascorbic acid 함량이 가장 크게 나타났고, 열수추출물과 아임계추출물은 유의적인 차이가 없었다(p<0.05).