• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4597-4606
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• 2023

Thermal analysis of the CANDU spent fuel dry storage canister is very important to ensure the integrity of the spent fuel. The analyses have been conducted using a conservative approach, with a particular focus on the peak cladding temperature (PCT) of the fuel rods in the canister. In this study, we have performed a realistic thermal analysis using a computational fluid dynamics (CFD) code. The canister contains 9 fuel bundle baskets. A detailed analysis of even a single basket requires significant computational resources. To overcome this challenge, we replaced each basket with an equivalent heat conductor (EHC), of which effective thermal conductivity (ETC) is developed from the results of detailed CFD calculations of a fuel bundle basket. Then, we investigated the effects of some conservative models, ultimately aiming at a realistic analysis. The results revealed: (i) The influence of convective heat transfer in the basket cannot be ignored, but it's less significant than expected. (ii) Modeling of the lifting rod is crucial, as it plays a decisive role in axial heat transfer at the center of the canister and significantly reduces the PCT. (iii) Convection within the canister is very important, as it not only reduces the PCT but also shifts its location upwards.

• Tunnel and Underground Space
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• v.33 no.2
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• pp.83-94
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• 2023

Unlike the conventional triaxial test cells for cylindrical specimens, which impose uniform lateral confining pressures, the GREAT (Geo-Reservoir Experimental Analogue Technology) cell can exert differential radial stresses using eight independently-controlled pairs of lateral loading elements and thereby generate horizontal stress fields with various magnitudes and orientations. In the preceding companion paper, GREAT cell tests were numerically simulated under different mechanical loading conditions and the validity of the numerical model was investigated by comparing experimental and numerical results for circumferential strain. In the present study, we simulated GREAT cell tests for an artificial sample containing a fracture under both mechanical loading and fluid flow conditions. The numerical simulation was carried out by varying the mechanical properties of the fracture surface, which were unknown. The numerical responses (circumferential strains) of the sample were compared with experimental data and a good match was found between the numerical and experimental results under certain mechanical conditions of the fracture surface. Additionally, the effect of fluid flow conditions on the mechanical behavior of the sample was investigated and discussed.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.328-336
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• 1999

To characterize the hydro-mechanical behavior of a rock joint, a rotary shear testing apparatus was devised in this study. Shear stress was driven by twisting the end of a sample in the rotary shear testing apparatus. The test results show that the rotary shear test underestimates the peak shear strength of a rock joint. The torque is known as a function of the radial distance from the axis of rotation, resulting in the radial variation of the shear stress. Fluid flow through rock joints is mainly dependent on the Joint roughness, contact area, initial aperture. To examine the dependency, the relationship between the hydraulic and the mechanical apertures for shear-flow was established by measuring the initial aperture. It shows that the mechanical aperture and the hydraulic aperture increase linearly with the dilatancy. The difference between the hydraulic and mechanical apertures describes the deviation from the behavior predicted by the parallel plate model.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.325-331
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• 2016

Computational fluid numerical analysis using the commercial code CFX was performed to develop a Pelton turbine for a pico hydro power generator using the circulating water of a cooling tower in a large building. The performance of the Pelton turbine was examined for different design factors, such as the bucket shape, in which the Pelton wheel was connected in an appropriate manner to the pipe section, and the number of buckets in order to find the optimal design of Pelton turbine for a pico hydro power using surplus water. A benchmark test was carried out on the manufactured small scale Pelton turbine to validate the design method of the Pelton turbine by numerical analysis. The results obtained by comparing the flow characteristics and power output measured using the ultrasonic flowmeter, the pressure transducer and the oscilloscope with the numerical results confirmed the validity of the analytical design method. The possibility of developing Pelton turbines for kW class pico hydro power generators using surplus water with an average circulation velocity of 1.2 m/s for the chosen bucket shape and number of buckets in a 30 m high building was confirmed.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.5
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• pp.618-626
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• 2012

Suppression of abnormal flow phenomena in the Francis hydro turbine is very important to improve the turbine performance. Especially, as cavitation and cavitation surge makes serious problems when the turbine is operated in the range of partial flow rate, optimum method of suppressing the abnormal flow characteristics is required necessarily. Moreover, as swirl flow in the draft tube of the Francis turbine decreases pressure at the inlet of the draft tube, suppression of the swirl flow can be an useful method of suppressing the occurrence of cavitation. In order to clarifying the possibility of suppressing the swirl flow by J-Groove in the draft tube, a series of CFD analysis has been conducted in the range of partial load, designed condition and excessive flow rate of a Francis turbine. A kind of J-Groove is designed and applied to the draft tube of the Francis hydro turbine model. The pressure contours, circumferential velocity vectors and vortex core regions in the draft tube are compared by the conditions with or without J-Groove. In addition, a group of data about the velocity in the draft is presented to show the influence of J-Groove.

• Ocean Systems Engineering
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• v.7 no.1
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• pp.21-38
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• 2017

In real sea environments, excessive dynamic axial tension variations can be exerted on the top-tensioned risers (TTRs) and lead to structural integrity issues. The traditional riser-tension-variation analysis, however, by using parametric formulation is only conditionally valid under certain strict limits and potentially underestimates the total magnitudes of tension variations. This phenomenon is especially important for the long stroke tensioner in dry-tree semisubmersible with larger global heave motion and longer stroke. In this paper, the hydro-pneumatic tensioner (HPT) is modeled in detailed component-level which includes a set of hydraulic and pneumatic components. The viscous fluid frictional effect in the HPT is considered. The main objectives are (i) to develop a detailed tension variation model of the HPT; (ii) to identify the deviations between the conventional parametric formulation and component-level formulation; (iii) to numerically analyze the tension variation of long stroke tensioner in a dry-tree semisubmersible (DTS). The results demonstrate the necessity of component-level formulation for long stroke tensioner in the development of DTS.

• Advances in Automotive Engineering
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• v.1 no.1
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• pp.1-20
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• 2018

The aim of this study is the optimization of the parameters of interconnected Hydro-Pneumatic (HP) suspension system of a three-axle vehicle for ride comfort and handling. For HP suspension systems of equivalent vertical stiffness and damping characteristics, interconnected HP suspension systems increase roll and pitch stiffness and damping characteristics of the vehicle as compared to unconnected HP suspension systems. Thus, they result in improved handling and braking/acceleration performances of the vehicle. However, increased roll and pitch stiffness and damping characteristics also increase roll and pitch accelerations, which in turn result in degraded ride comfort performance. Therefore, in order to improve both ride comfort and vehicle handling performances simultaneously, an optimum parameter set of an interconnected HP suspension system is obtained through an optimization procedure. The objective function is formed as the sum of the weighted vertical accelerations according to ISO 2631. The roll angle, one of the important measures of vehicle handling and driving safety, is imposed as a constraint in the optimization study. Upper and lower parameter bounds are used in the optimization in order to get a physically realizable parameter set. Optimization procedure is implemented for a three-axle vehicle with unconnected and interconnected suspension systems separately. Optimization results show that interconnected HP suspension system results in improvements in both ride comfort and vehicle handling performance, as compared to the unconnected suspension system. As a result, interconnected HP suspension systems present a solution to the conflict between ride comfort and vehicle handling which is present in unconnected suspension systems.

• Journal of Welding and Joining
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• v.29 no.2
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• pp.34-39
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• 2011

Nickel-based austenitic alloys such as Alloy 82 and 182 had been employed as the weld metals in nuclear power plants (NPPs) due to their high corrosion resistance as well as good mechanical properties. However, since the 2000s, the occurrence of primary water stress corrosion cracking has been reported in conjunction with these alloys in domestic and oversea NPPs. In the present work, we assumed an imaginary crack at the inner surface of a surge nozzle weld that had previously experienced the outside repair welding, and constructed its finite element model. Finite element analysis was performed with respect to the heat transfer, and then to the residual stress for obtaining the total applied stress distributions. These stress distributions were finally converted to the stress intensity factors for estimating crack growth rate. From the comparison of crack growth rate curves for the cases of no repair welding and outside repair welding, it was found that the outside repair welding did not exhibit negative effect on the crack growth for the surge nozzle under consideration in this work; in both cases, the cracks stopped growing before they became the through-wall cracks.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1526-1529
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• 1994

In hydro-generator, a groundwall insulation of stator windings gradually deteriorates due to mechanical, thermal, electrical and environmental stresses. These stresses combine to result in loose windings, delamination of the stator insulation and/or electrical tracking of the end winding, all of which can lead to stator insulation failures. Conventionally, off-line tests such as partial discharge measurement, DC/AC current test and ${\Delta}tan{\delta}$ test has been used for estimation of winding condition. However, off-line test requires large power supply and generator outage. In addition, major cause of insulation problems such as loose wedges and slot discharges may not be found with off-line diagnoses. This paper describes the on-line partial discharge measurement techniques in the generator stator windings. The experimental results from the UIAM #1 hydro-generator confirms a optimistic application of on-line generator diagnosis method as a reliable tool for evaluation of winding condition.

• Nuclear Engineering and Technology
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• v.40 no.1
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• pp.77-86
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• 2008

This paper describes the nonlinear analyses of a 1:4 scale model of a prestressed concrete containment vessel (PCCV) using an axisymmetric model and a three-dimensional model. These two models are refined by comparison of the analysis results and with testing results. This paper is especially focused on the analysis of behavior under pressure and the temperature effects revealed using an axisymmetric model. The temperature-dependent degradation properties of concrete and steel are considered. Both geometric and material nonlinearities, including thermal effects, are also addressed in the analyses. The Menetrey and Willam (1995) concrete constitutive model with non-associated flow potential is adopted for this study. This study includes the results of the predicted thermal and mechanical behaviors of the PCCV subject to high temperature loading and internal pressure at the same time. To find the effect of high temperature accident conditions on the ultimate capacity of the liner plate, reinforcement, prestressing tendon and concrete, two kinds of analyses are performed: one for pressure only and the other for pressure with temperature. The results from the test on pressurization, analysis for pressure only, and analyses considering pressure with temperatures are compared with one another. The analysis results show that the temperature directly affects the behavior of the liner plate, but has little impact on the ultimate pressure capacity of the PCCV.