• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.7
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• pp.658-664
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• 2010

A control element drive mechanism(CEDM) is a reactor regulating system, which inserts, withdraws or maintains a control rod containing a neutron absorbing material within a reactor core to control the reactivity of the core. The ball-screw type CEDM for the integral reactor has a spring-damper system to reduce the impact force due to the scram of the CEDM. This paper describes the experimental results to obtain the drop and damping characteristics of the CEDM. The drop tests are performed by using a drop test rig and a facility. A drop time and a displacement after an impact are measured using a LVDT. The influences of the rod weight, the drop height and the flow area of hydraulic damper on the drop and damping behavior are also estimated on the basis of test results. The drop time of the control element is within 4.5s to meet the design requirement, and the maximum displacement is measured as 15.6 mm. It is also found that the damping system using a spring-hydraulic damper plays a good damper role in the CEDM.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.1-8
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• 2015

When the line and switchgear of the substation system are disconnected, ferro-resonance can occur. This happens even if the capacitive reactance and inductive reactance are not equal, which are not common resonance conditions. Resonance conditions vary depending on the busbar configuration environment. Although the damping resistance method applying the existing saturable reactor to cope with ferro-resonance has been successfully applied on site, there can be loss of normal function during long-term operation. The reason is because the rise in the operating frequency of saturable reactors means the saturation number is increased. Therefore, it can no longer function as saturable reactor since the resistor having inadequate capacity is burned out. To address this problem, in this paper, an EMTP-based simulation test was performed by designing and applying a dual reactor method, which adds an extended divergence reactor to the 1st side of the VT. The test result confirms that when the divergence reactor is inserted, the voltage and current values obtained at the 1st side and 2nd side of the VT as well as current values of divergence reactor part were stabilized from the transient phenomena and return to normal values. When compared with existing measures, although this method is similar in adding having a reactor added to a system regarding ferro-resonance, it has the advantage of being able to prevent ferro-resonance in advance since the reactor is added before the system is saturated. In addition, because it does not use damping resistance, it can extend the equipment life and stabilize its operation. Therefore, there are a lot of differences in terms of its operating characteristics and achivement of goal between the conventional method and new divergence reactor method.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.457-466
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• 2003

In this paper, the numerical finite element formulations were derived for the linearized Navier-Stokes' equations with assumptions of two-dimensional incompressible, homogeneous viscous fluid field, and small oscillation and the FAMD (Fluid Added Mass and Damping) code was developed for practical applications calculating the fluid added mass and damping. In formulations, a fluid domain is discretized with C$\^$0/-type quadratic quadrilateral elements containing eight nodes using a mixed interpolation method, i.e., the interpolation function for the velocity variable is approximated by a quadratic function based on all eight nodal points and the interpolation function for the pressure variable is approximated by a linear function based on the four nodal points at vertices. Using the developed code, the various characteristics of the fluid added mass and damping are investigated for the concentric cylindrical shell and the actual hexagon arrays of the liquid metal reactor cores.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.1021-1026
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• 1995

The seismic responses of a base isolated Pressurized Water Reactor (PWR) are investigated using a mathematical model which expresses the superstructure as lumped mass-spring model and the seismic isolator as an equivalent spring-damper. Time history analyses are performed for the 1940 E1 Centre earthquakes in both horizontal and vertical directions. In the analysis, structural damping of 5% is used for the superstructure. The isolator damping ratios of 12% for horizontal and 5% for vertical directions are used. The acceleration responses in base isolated PWR superstructure with high damping rubber bearings are much smaller than those in fixed base structure in horizontal direction. However, the vertical acceleration responses at the superstructure in the base isolation system are amplified to some extent. It is suggested that the vertical seismic responses at the superstructure should be reduced by introducing a soft vertical isolation device.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.276-276
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• 2003

This paper dealt with an experimental study on the free vibration of circular-tube-beam submerged in water. A circular-tube-beam is commonly founded on the nuclear fuel assembly system in nuclear reactor. The nuclear fuel assembly susceptible to flow-induced vibration in nuclear reactor. So, the nuclear fuel assembly be designed to avoid any resonance due to the vibration during the reactor operation. In the experiment, applied boundary condition is clamped-free and the effect of water height to natural frequency and damping is studied. The experiment in air and in water has been performed. Used experimental method is impact exciting method. The natural frequencies and damping ratio according to water height is presented.

• Structural Engineering and Mechanics
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• v.59 no.2
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• pp.291-312
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• 2016

Seismic performance evaluation of shear wall is essential as it is the major lateral load resisting member of a structure. The ultimate load and ultimate drift of the shear wall are the two most important parameters which need to be assessed experimentally and verified analytically. This paper comprises the results of monotonic tests, quasi-static cyclic tests and shake-table tests carried out on a midrise shear wall. The shear wall considered for the study is 1:5 scaled model of the shear wall of the internal structure of a reactor building. The analytical simulation of these tests is carried out using micro and macro modeling of the shear wall. This paper mainly consists of modification in the hysteretic macro model, developed for RC structural walls by Lestuzzi and Badoux in 2003. This modification is made by considering the stiffness degradation effect observed from the tests carried out and this modified model is then used for nonlinear dynamic analysis of the shear wall. The outcome of the paper gives the variation of the capacity, the failure patterns and the performance levels of the shear walls in all three types of tests. The change in the stiffness and the damping of the wall due to increased damage and cracking when subjected to seismic excitation is also highlighted in the paper.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.48-48
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• 1999

• Nuclear Engineering and Technology
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• v.30 no.2
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• pp.83-90
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• 1998

To predict effects of seismic isolation, seismic isolation bearings were applied to the Wolsong reactor building and the analytical study was performed. For this study, the Wolsong reactor building was modeled using lumped masses and beam elements. Design Basis Earthquake with a ground acceleration of 0.2g was applied. And then, the behavior of the isolated structure was compared with that of the unisolated structure. The horizontal response acceleration at the top of the unisolated reactor building was 0.99g, while that of the isolated one was 0.14g(15% damping) and the acceleration response along the height of the structure was constant. The maximum displacement of the unisolated structure was 8.3mm, while that of the isolated structure was 66mm. The application of isolation bearings on the reactor building reduces seismic loads but increases the displacement of the structure on a large scale. Therefore, when using isolation bearings, the reactor building and BOP should be located on a common mat to cover the large displcement.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.04a
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• pp.99-106
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• 1995

The seismic responses of a base Isolated Pressurized Water Reactor(PWR) are investigated using a mathematical model which expresses the superstructure as a linear lumped mass-spring and the seismic Isolator as an equivalent spring-damper. Time history analyses are performed for the 1940 El Centre earthquake with linear amplification. In the analysis 5% of structural damping is used for the superstructure. The effects of high damping rubber bearing on seismic response of the superstructure in base isolated system are evaluated for four stiffness model types. The acceleration responses in base isolated PWR superstructure with high damping rubber bearings are much smaller than those in fixed base structure. In the higher strain region where stiffness behaves non-linearly, the acceleration responses modelled by one equivalent stiffness are smaller than those in nonlinear spring model, and the higher stiffness spring model of isolator exhibits larger peak acceleration response at superstructure in the frequency range above 2.0 Hz. when subjected to linearly amplified 1940 El Centre earthquake.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.7
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• pp.442-447
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• 1988

Saturable reactor-resistor pair is proposed as a part of snubber and applied to a hard commutation chopper. SCR turn off process is modeled to simulate the hard commutation chopper. State equations are derived for each mode of the chopper and they are solved by Runge-Kutta 4th order method. It is shown that the reverse voltage spike and reverse dv/dt can be minimized by applying saturable reactor-resistor pair to the chopper which controls peak reverse recovery current and damping factor. Saturable reactor-resistor pair can be used to reduced SCR power loss and value of snubber capacitor and can be applied to high power thyristor devices.