• Nuclear Engineering and Technology
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• 제53권9호
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• pp.2847-2858
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• 2021

When a nuclear reactor with rectangular fuel assemblies runs for a long time, impurities and debris may be taken into coolant channels, which may cause flow blockage, and the blocked fuel assemblies might be destroyed. Therefore, the purpose of this study is to perform a thermal-hydraulic analysis of a rectangular fuel assembly by STAR-CCM+, under the condition of one subchannel with 80% blockage ratio. A rectangular fuel assembly of the International Atomic Energy Agency (IAEA) 10 MW material test reactor (MTR) is chosen. In view of the gasket material taken into the coolant channel is close to the single side of the coolant channel, in the flow blockage accident of the Oak Ridge Research Reactor (ORRR), a new blockage category called single side blockage is attempted. The blockage positions include inlet, middle and outlet, and the blockage is set as a cuboid. It is found by simulations that the blockage redistributes the mass flow rate, and large vortices appear locally. The peak temperature of the cladding is maximum, when the blockage is located at the single side of the coolant channel inlet, and no boiling occurs in all blockage cases. Moreover, as the height of the blockage increases, the damage caused by the blockage increases slightly.

• 수산해양기술연구
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• 제55권3호
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• pp.252-263
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• 2019

In order to understand the tidal current and mean flow at the west channel of Yeoja Bay in the South Sea of Korea, numerical model experiments and vorticity analysis were carried out. The currents flow north at flood and south at ebb respectively and have the reversing form in the west channel. Topographical eddies are found in the surroundings of Dunbyong Island in the east of the channel. The flood currents flow from the waters near Naro Islands through the west channel and the coastal waters near Geumo Islands through the east channel. The ebb currents from the Yeoja Bay flow out along the west and the east channels separately. The south of Nang Island have weak flows because the island is located in the rear of main tidal stream. Currents are converged at ebb and diverged at flood in the northwest of Jeokgum Island. Tidal current ellipses show reversing form in the west channel but a kind of rotational form in the east channel. As the results of tide induced mean flows, cyclonic and anticyclonic topographical eddies at the northern tip but eddies with opposite spin at the southern tip are found in the west channel of Yeoja Bay. The topographical eddies around the islands and narrow channels are created from the vorticity formed at the land shore by the friction between tidal currents and the west channel.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3540-3550
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• 2022

The supercritical carbon dioxide (S-CO₂) Brayton cycle is an important energy conversion technology for the fourth generation of nuclear energy. Since the printed circuit heat exchanger (PCHE) used in the S-CO₂ Brayton cycle has narrow channels, Rayleigh-Bénard (RB) convection is likely to exist in the tiny channels. However, there are very few studies on RB convection in supercritical fluids. Current research on RB convection mainly focuses on conventional fluids such as water and air that meet the Boussinesq assumption. It is necessary to study non-Boussinesq fluids. PRB convection refers to RB convection that is affected by horizontal incoming flow. In this paper, the computational fluid dynamics simulation method is used to study the PRB convection phenomenon of non-Boussinesq fluid-supercritical carbon dioxide. The result shows that the inlet Reynolds number (Re) of the horizontal incoming flow significantly affects the PRB convection. When the inlet Re remains unchanged, with the increase of Rayleigh number (Ra), the steady-state convective pattern of the fluid layer is shown in order: horizontal flow, local traveling wave, traveling wave convection. If Ra remains unchanged, as the inlet Re increases, three convection patterns of traveling wave convection, local traveling wave, and horizontal flow will appear in sequence. To characterize the relationship between traveling wave convection and horizontal incoming flow, this paper proposes the relationship between critical Reynolds number and relative Rayleigh number (r).

• 한국항해학회지
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• 제24권5호
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• pp.423-433
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• 2000

Nowadays LNG has been beginning to take the place of petroleum as fuel all over the world and VLCC of LNG will take the same sea routes that had been used by VLCC tankers of petroleum in the last part of the 20th century. The transportation of LNG by a VLCC include more dangerous nature of sea peril than that of petroleum. We already know the dimensions of a disaster a LNG tanker could bring about in the case of the LNG tanker, Yuyo-Maru No. 10 in the Tokyo Bay of Japan in 1974. From the point of safety when we construct a LNG base or LNG pier in the base, the appropriate government authority and constructing company had better take sea pilots or some ships handling experts to participate in a prior consultation of the design of the project. A G/T 100,000 ton LNG base and pier were completed in November of 1996 in Inchon harbour in Korea and VLCC of LNG of G/T 100,000 ton class have been entering into the base ever since. This study was started and completed In comply with the requisition of the Sea Pilot Association of Inchon harbour in advance of the opening of the LNG base. As the entrance and exit channels leading to Inchon harbour were constructed in the years of 1930s, it was one of the most pressing works for Inchon sea pilots in 1996 to certify the method of safe passing maneuvering of a G/T 100,000 ton of LNG tanker through the Pudo narrow channel prior to commencing actual piloting of the VLCC of LNG. The authors made some mathematical models computing maneuvering of a vessel changing her course with her control surface through a narrow channel and computed maneuvering of a G/T 100,000 ton of LNG tanker and also made maneuvering simulations of the vessel by a desk-top simulator. The results of computations and simulations are well coincided with each other in qualitative aspects to assure safe passing of the VLCC of LNG.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2000년도 Proceeding of CIN-KIN Joint Symposium 2000 on M.E.T. Under STCW 78/95 and SINO-KOREA MARITIME CONTACT IN MID-CENTURIES
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• pp.115-155
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• 2000

Nawadays LNG has been beginning to take the place of petroleum as fuel all over the world and VLCC tankers of LNG will take the same sea routes that had been used by VLCC tankers of petroleum in the last pat of he 20th century. The transportation of LNG by a VLCC include more dangerous nature of sea peril than that of petroleum. We already know the dimensions of a disaster a LNG tanker could bring about in the case of the LNG tanker, Yuyo-Maru No. 10 in the Tokyo Bay of Japan in 1974. From the point of safety when we construct a LNG base or LNG pier in the base, the appropriate government authority and constructing company had better take sea pilots or some ships handling experts to participate in a prior consultation of the design of the project. A G/T 100,000 ton LNG base and pier were completed in November of 1996 in Inchon harbour in Korea and LNG VLCC tankers of G/T 100,000 ton class have been entering into the base ever since. This study was started and completed to comply with the requisition of the Sea Pilot Association of Inchon harbour in advance of the opening of the LNG base. As the entrance and exit channels leading to Inchon harbour were constructed in the years of 1930s, it was one of the most pressing works for Inchon sear pilots in 1996 to certify the method of safe passing maneuvering of a G/T 100,000 ton LNG tanker through the Pudo narrow channel prior to commercing actual piloting of the LNG VLCC tanker. The author made some mathematical models computing maneuvering of a vessel changing her course with her control surface through a narrow channel and computed maneuvering of a G/T 100,000 ton LNG tanker and also made maneuvering simulations of the vessel by a desk-top simulator. The results of computations and simulations are well coincided with each other in qualitative aspects to assure safe passing of the LNG VLCC.

• Nuclear Engineering and Technology
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• 제37권6호
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• pp.565-574
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• 2005

The CANFLEX Mk-V bundle is designed to improve upon the critical heat flux (CHF) characteristics of the CANFLEX Mk-IV bundle. The main difference between these two bundles is an increase in bearing pad height of about 0.3 mm in the CANFLEX Mk-IV bundle. This change in bearing pad height leads to an increase in gap flow at the bottom of the bundle, primarily eliminating the localized narrow-gap effect that limits the CHF of the CANFLEX Mk-IV bundle. The objective of this paper is to examine the effects of bearing pad height and pressure tube creep on the sheath-temperature distribution, dryout power, and dryout location, as observed ken full-scale bundle tests, between CANFLEX Mk-IV and Mk-V bundles In uncrept and crept channels. A comparison of surface-temperature differences between the top and bottom elements of the bundles showed that increasing the bearing pad height has led to a more homogeneous enthalpy distribution in subchannels of the bundle. Initial dryout locations of the CANFLEX Mk-V bundle were mainly observed at the mid-spacer plane of either the $10^{th}$ (about $80\%$) or $11^{th}$ ($20\%$) bundle in the 12-bundle string, as compared to the mid-spacer and downstream-button planes for the CANFLEX Mk-IV bundle. Dryout power and boiling-length-average (BLA) CHF values exhibit consistent trends and little scatter with varying flow conditions for both types of CANFLEX bundles in uncrept and crept channels. An increase in pressure tube creep has led to a reduction in dryout power (about $20\%$ far the $3.3\%$ crept channel and $27\%$ for the $5.1\%$ crept channel as compared to dryout powers for the uncrept channel). Increasing the bearing pad height of the CANFLEX bundle has led to an increase in the dryout power. Overall, the dryout power of the CANFLEX Mk-V bundle is 7 to $10\%$ higher than that of the CANFLEX Mk-IV bundle at the inlet temperature range of interest (i.e., between 243 and $290^{\circ}C$).

• Korean Chemical Engineering Research
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• 제54권6호
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• pp.863-870
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• 2016

본 논문의 목적은 소듐냉각고속로(sodium cooled fast reactor, SFR)와 초임계 $CO_2$ Brayton cycle의 연계 시, 원자로 열수송 계통과 동력변환 계통의 압력 경계를 형성하는 회로인쇄형 열교환기의 경계면에 균열이 발생해 고압(약 200 bar)의 $CO_2$가 상압 수준의 액체소듐유로 측에 유입되었을 때의 물리/화학적 현상을 파악하여 열교환기 설계에 활용 가능한 실험 자료를 생산하는 것이다. 열교환기의 소듐-$CO_2$ 경계면 균열 현상은 경계면의 균열 크기에 따라 미세 균열에 의한 소듐유로막힘(plugging) 현상과 상대적으로 큰 균열에 의한 열교환기 재료손상(wastage) 현상으로 나뉜다. Plugging 실험결과, 소듐유로 직경이 3mm일 때 $CO_2$ 주입 즉시 소듐 흐름이 정지한 반면 소듐유로 직경이 5 mm일 때는 유량이 감소되기 시작하는 시점은 3 mm의 경우와 유사하게 $CO_2$ 주입 즉시 나타났지만 소듐의 흐름이 완전히 정지할 때까지는 상대적으로 오랜 시간이 소요되었다. 이러한 실험결과는 실제 열교환기의 소듐-$CO_2$ 경계면에서 미세균열이 발생했을 때, 소듐유로 직경이 3 mm로 좁을 경우 균열 발생과 동시에 해당 소듐유로가 반응생성물에 의해 막혀 해당 유로 외의 유로들로 지속적인 열교환기 운전이 가능하지만, 소듐유로의 직경이 5 mm로 넓어질 경우 소듐유로가 고체생성물에 의해 즉시 막히지 않고 생성물이 소듐유로를 따라 계통 내부를 이동하다 일정 농도 이상이 되어야 소듐유로를 막게 할 것으로 예상할 수 있는 결과이다. Wastage 실험결과, 열교환의 재질(STS316, Inconel600, G91 합금강), 운전온도($400{\sim}500^{\circ}C$), 노즐직경(0.2~0.8 mm), 시편-노즐 거리(2~6 mm)와 무관하게 고압(약 200~250 bar)의 $CO_2$ 분사에 의한 시편의 물리적 손상(erosion) 현상은 발생하지 않았다. 노즐에서의 분사되는 $CO_2$의 분사속도는 마하 0.4~0.7인 것으로 확인되었다. 본 연구의 실험결과는 열교환기 파손 대처 설계에 배경 실험 자료로 활용될 것으로 기대된다.

• Journal of electromagnetic engineering and science
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• 제8권2호
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• pp.41-46
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• 2008

A bandwidth and power efficient high speed ubiquitous sensor network(USN) for realizing a ubiquitous society is a great challenge for researcher community. In this paper we incorporate a cooperative transmission protocol within a special type of multi-code modulation to meet these requirements. Multi-code(Mc) modulation has been developed for high-speed data transmission over wireless channels. We proposed a new class of orthogonal codes for multi-code modulation which is an orthogonal subset of orthogonal codes(OSOC). Our proposed OSOC structure allows us to use only one relay to cooperate M nodes that effectively reduces the bandwidth and power requirement. This protocol is similar to spread-spectrum(SS) technique that can reduce both broad and narrow band jamming.

• 소음진동
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• 제5권3호
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• pp.373-383
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• 1995

From the viewpoint of the structural design, the principal problem of the heat exchanger is the potentiality of structural instabilities due to the fluid loading effect during operations. Excessive fluid loading may give rise to permanent deformation of tube and would enentually result in collapse of heat exchanger, which would cause an obstruction of the fluid flow in the narrow channels. In this study, a fluid-structural interaction model was developed to investigate analtically the vibration characteristics of thin rectangular tube used in the heat exchanger. The model consists of two flat plates separated by fluid. The effects of the fluid in the tube was stuided. For analyses, the natural frequency coefficients of the model were investigated for the plate aspect ratios, channel heights, and boundary conditions. As conclusions, the natural frequency coefficients of the tube is found to be affected largely by the fluid loading and the channel heights.

• 한국정보통신학회논문지
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• 제7권3호
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• pp.390-394
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• 2003

다양한 이동통신 채널의 모의구현은 시스템 구현 및 검증에 매우 중요한 요소이다. 따라서 본 논문에서는 이동통신 채널을 효율적으로 모의할수 있는 방법을 제안하였다. 새롭게 제안된 방법은 주어진 도플러 스펙트럼 모델로부터 협대역 이동통신 채널의 발생을 가능하게 함으로서 신호대 잡음비, 직접 및 간접 전파경로, 신호전력등의 다양한 전파환경을 고려한 채널의 구현이 가능하다.