• 한국압력기기공학회 논문집
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• 제4권2호
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• pp.1-6
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• 2008

Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source for nuclear hydrogen generation. The VHTR can produce hydrogen from heat and water by using a thermo-chemical process or from heat, water, and natural gas by steam reformer technology. A co-axial double-tube primary hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger (IHX) for the VHTR. In this study, a preliminary design analysis for the primary HGD of the nuclear hydrogen system was carried out. These preliminary design activities include a determination of the size, a strength evaluation and an appropriate material selection. The determination of the size was undertaken based on various engineering concepts, such as a constant flow velocity model, a constant flow rate model, a constant hydraulic head model, and finally a heat balanced model.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.285-290
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• 1994

The influence of elevated temperatures on the mechanical properties of concrete is important for fire-resistance studies and also for understanding the behavior of containment vessel, such as nuclear reactor pressure vessels, during service and ultimate condition. The present study is to clarify the damage/deterioration of concrete structures that are subjected to high temperature exposure. To this end, comprehensive experiments are conducted. The major test variables are the peak temperatures, rate of temperature increase, and sustained duration at peak temperature. The results include weight loss residual compressive strength and stress-strain curve. From those results, residua compressive strength formula and stress-strain relationship are proposed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.87-92
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• 2001

In this paper, high strength pressure vessel steels having the same chemical compositions were manufactured by the two different steel-making processes, such as vacuum degassing(VD) and electro-slag remelting(ESR) methods. After the steel-making process, they were normalized at $955^{\circ}C$, quenched at $843^{\circ}C$, and finally tempered at $550^{\circ}C$ or $450^{\circ}C$, resulting in tempered martensitic microstructures with different yielding strengths depending on the tempering conditions. Low-cycle fatigue(LCF) tests, fatigue crack growth rate(FCGR) tests, and fracture toughness tests were performed to investigate the fatigue and fracture behaviors of the pressure vessel steels. In contrast to very similar monotonic, LCF, and FCGR behaviors between VD and ESR steels, a quite difference was noticed in the fracture toughness. Fracture toughness of ESR steel was higher than that of VD steel, being attributed to the removal of impurities in steel-making process.

• Nuclear Engineering and Technology
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• 제54권1호
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• pp.357-373
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• 2022

The high-temperature gas-cooled reactor pebble-bed module project is the first commercial Generation-IV NPP(Nuclear Power Plant) in China. A new joint is used for the vertical support of RPV(Reactor Pressure Vessel). The steel corbel is integrally embedded into the reactor-cabin wall through eight asymmetrically arranged pre-stressed high-strength bolts, achieving the different path transmission of shear force and moment. The vertical monotonic loading test of two specimens is conducted. The results show that the failure mode of the joint is bolt fracture. There is no prominent yield stage in the whole loading process. The stress of bolts is linearly distributed along the height of corbel at initial loading. As the load increases, the height of neutral axis of bolts gradually decreases. The upper and lower edges of the wall opening contact the corbel plate to restrict the rotation of the corbel. During the loading, the pre-stress of some bolts decreases. The increase of the pre-stress strength ratio of bolts has no noticeable effect on the structure stiffness, but it reduces the ultimate bearing capacity of the joint. A simplified calculation model for the elastic stage of the joint is established, and the estimation results are in good agreement with the experimental results.

• Nuclear Engineering and Technology
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• 제45권4호
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• pp.469-476
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• 2013

In a postulated severe core damage accident in a PHWR, multiple failures of core cooling systems may lead to the collapse of pressure tubes and calandria tubes, which may ultimately relocate inside the calandria vessel forming a terminal debris bed. The debris bed, which may reach high temperatures due to the decay heat, is cooled by the moderator in the calandria. With time, the moderator is evaporated and after some time, a hot dry debris bed is formed. The debris bed transfers heat to the calandria vault water which acts as the ultimate heat sink. However, the questions remain: how long would the vault water be an ultimate heat sink, and what would be the failure mode of the calandria vessel if the heat sink capability of the reactor vault water is lost? In the present study, a numerical analysis is performed to evaluate the thermal loads and the stresses in the calandria vessel following the above accident scenario. The heat transfer from the molten corium pool to the surrounding is assumed to be by a combination of radiation, conduction, and convection from the calandria vessel wall to the vault water. From the temperature distribution in the vessel wall, the transient thermal loads have been evaluated. The strain rate and the vessel failure have been evaluated for the above scenario.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2836-2846
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• 2020

During severe nuclear power plant (NPP) accidents, a H₂/CO mixture can be generated in the reactor pressure vessel by core degradation and in the containment as well by molten corium-concrete interaction. In spite of its importance, a state-of-the-art methodology predicting H₂/CO combustion risk relies predominantly on empirical correlations. It is therefore necessary to develop a proper methodology for flammability evaluation of H₂/CO mixtures at ex-vessel phases characterized by three factors: CO concentration, high temperature, and diluents. The developed methodology adopted Le Chatelier's law and a calculated non-adiabatic flame temperature model. The methodology allows the consideration of the individual effect of the heat transfer characteristics of hydrogen and carbon monoxide on low flammability limit prediction. The accuracy of the developed model was verified using experimental data relevant to ex-vessel phase conditions. With the developed model, the prediction accuracy was improved substantially such that the maximum relative prediction error was approximately 25% while the existing methodology showed a 76% error. The developed methodology is expected to be applicable for flammability evaluation in chemical as well as NPP industries.

• Korean Chemical Engineering Research
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• 제54권3호
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• pp.350-359
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• 2016

본 연구는 vessel blowdown 시 발생하는 온도와 압력 변화를 보다 정확히 예측하기 위하여 기존에 개발된 dynamic model을 기반으로 새로운 모델을 개발하고, 개발한 모델의 정확도를 높이기 위하여 vessel 내부의 흐름이 층류일 때와 난류일 때를 모두 고려하여 vessel 벽면으로부터 기체로의 열 전달량을 계산하였다. 효율적인 열역학 계산을 위해 일체의 계산식은 압력이 감소하는 단계 별로 나누어 진행하였으며 계산의 부담을 덜어주면서 계산의 정확도를 유지하기 위한 압력변화 size를 결정하였다. 개발한 모델에 Peng-Robinson equation과 Soave-Redlich-Kwong equation을 적용하여 각각의 경우에 따른 결과의 차이를 비교하였다. 마지막으로 모델의 검증을 위해 Haque et al.의 실험조건을 동일하게 적용하여 실험 결과와 시뮬레이션 결과를 비교 하였으며, 이를 통해 모델의 정확도를 입증하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권5호
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• pp.707-716
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• 2008

The objective of this study was to analyze the effect of mixed fuel composition and mass fraction on spray inner structure in evaporating transient spray under the variant ambient conditions. Spray structure and spatial distribution of liquid phase concentration were investigated using a thin laser sheet illumination technique on the three component mixed fuels. A pulsed Nd:YAG laser was used as a light source. The experiments were conducted in a constant volume vessel with optical access. Fuel was injected into the vessel with electronically controlled common rail injector. Used fuel contains i-octane($C_8H_{18}$), n-dodecane($C_{12}H_{26}$) and n-hexadecane($C_{16}H_{34}$) that were selected as low-, middle- and high-boiling point fuel, respectively. Experimental conditions are 42 MPa, 72 MPa and 112 MPa in injection pressure, $5\;kg/m^3$, $15kg/m^3$ and $30kg/m^3$ in ambient gas density, 300 K, 500 K, 600 K and 700 K in ambient gas temperature, 300 K and 368 K in fuel temperature and different fuel mass fraction. Experimental results indicated that the multi-component fuels made two phase region mixed vapor and liquid so that it would are helpful to improve combustion, for the fuels of high boiling point component could accelerate evaporation very much according as low boiling point fuel was added to high boiling point fuel.

• Journal of Welding and Joining
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• 제11권4호
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• pp.103-111
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• 1993

Recently, several high-tensile steels(e.g. 80kg and above, $2^{1/4}Cr$-1Mo)having good quality to high temperature and pressure-resistance are widely used to construct petroleum-plant and pressure vessel of heat or nuclear-power plant. However, in the steels, reheating crack at grain boundaries of the heat affected zone(HAZ) occures during post welding heat treatment(PWHT)to remove welding residual stress. In order to study theoretically the characteristics of reheating crack created by PWHT, the computer program of three-dimensional thermal-elasto-plasto-creep analysis based on finite element method are developed, and then the mechanical behavior(history of creep strain accumulation and stress relaxation, etc)of welded join in thick plate during PWTH is clarified by the numerical results.

• 한국화재소방학회논문지
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• 제15권1호
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• pp.16-22
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• 2001

석유화학플랜트에서 다량 부산되는 가연성 고체인 PP(Polypropylene) 및 LLDPE(Linear low density polyethylene)의 열적특성과 압력용기를 이용하여 산화제와의 혼촉위험성을 조사하였다. 시차주사열량계 및 열중량 분석기를 이용하여 온도에 따른 발열개시온도 및 중량감소를 조사하였고, PP 및 LLDPE의 혼촉위험성을 살펴보고자 소방법상 제1류 위험물로 분류되고 있는 몇 가지 대표적인 산화성 고체와 혼합하여 무게비에 따른 압력용기 내에서의 혼촉위험성을 조사하였다. 또한 가스농도 측정기를 이용하여 PP 및 LLDPE에 대한 연소생성물의 농도를 측정하였다. DSC분석 결과 열분해에 따른 발열 피크가 PP의 경우 220~$250^{\circ}c$ 부근에서 나타나고 있으며, TGA분석결과 PP 및 LLDPE의 분해온도는 각각 200~$350^{\circ}c$, 300~$500^{\circ}c$ 범위이다. 압력용기 시험에 의한 산화제와 PP 및 LLDPE 분진의 혼촉위험성은 오리피스 직경이 감소할수록, 산화제와의 혼촉 무게비가 증가할수록 그리고 시료의 분해온도와 산화제의 분해온도가 비슷한 경우 흔촉위험성이 크게 나타났다. 또한 시료의 연소가스 분석결과 PP의 경우 LLDPE보다 상당히 많은 양의 일 산화탄소가 발생하는 반면 LLDPE가 PP보다 더 많은 양의 이산화탄소 가스를 발생하였다.