• Nuclear Engineering and Technology
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• v.33 no.1
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• pp.12-24
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• 2001

The post-LOCA long term cooling (LTC) performance of the Korean Standard Nuclear Power Plant (KSNPP) is analyzed for both small break loss-of-coolant accidents (LOCA) and large break LOCA at cold leg. The RELAP5/MOD3.2.2 beta code is used to calculate the LTC sequences based on the LTC plan of the Korean Standard Nuclear Power Plants (KSNPP). A standard input model is developed such that LOCA and the followed LTC sequence can be calculated in a single run for both small break LOCA and large break LOCA. A spectrum of small break LOCA ranging from \ulcorner.02 to 0.5 k2 of break area and a double-ended guillotine break are analyzed. Through the code calculations, the thermal-hydraulic behavior and the boron behavior are evaluated and the effect of the important action including the safety injection tank (SIT isolation and the simultaneous injection in LTC procedure is investigated. As a result, it is found that the sufficient margin is available in avoiding the boron precipitation in the core. It is also found that a further specific condition for the SIT isolation action need to be setup and it is recommended that the early initiation of the simultaneous injection be taken for larger break LTC sequences.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.435-440
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• 1996

Large Loss-of-Coolant Accidents analyzed in Final Safety Analysis Reports are usually covered by Reactor Inlet Header. Reactor Outlet Header and Primary Pump Suction breaks as representative cases. In this study we analyze the total (guillotine) break of an Emergency Core Cooling System (ECCS) pipe located at the ECCS injection point into the Primary Heat Transport System (PHTS). It was expected that thermal-hydraulic behaviors in the PHT and ECC systems are different from those of a Reactor Inlet Header break, having an equivalent break size. The main purpose of this study is to get insights on the differences occurred between the two cases and to assess these differences from the phenomenon behavior point of view. It was also investigated whether the ECCS line break analysis results could be covered by header break analysis results. The study reveals that as the intact loop has almost the same behavior in both analyzed cases. broken loop behavior is different mostly regarding sheath temperature in the critical core pass and pressure decrease in the broken Reactor Inlet Header. Differences are also met in the ECCS behavior and in event sequences timings.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.677-682
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• 2002

Break-in is an intentional treatment to enhance the performance life of machinery parts and to maintain static friction behavior. Most studies on break-in have concerned only about surface conditions such as roughness or film formation. But the exact mechanism of break-in has not been found yet. Friction, scuffing behavior and wear of AISI 1045 were studied in relation to break-in and residual stress. The cylinder-on-disk type tribometer was used with the line-contact geometry. Scuffing tests were carried out using a constant load of 730N. In the break-in procedure the step load was applied from 100N to 200N. In this experiment, it was found that the break-in helps compressive residual stress to be formed well enough to enhance the scuffing life during the scuffing test. Specimens that had high compressive residual stress induced by shot-peening show better wear resistance than those were not shot-peened. Results of scuffing test, break-in procedure and wear amount in relation to residual stress have been discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.360-361
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• 2005

Rapid progress in IC fabrication technology has strong demand in polishing of silicon wafer to meet the tight specification of nanotopography and surface roughness. One of the important issues in Si CMP is the stabilization of polishing pad. If a polishing pad is not stabilized before main Si wafer polishing process, good polishing result can not be expected. Therefore, new pad must be subjected into break-in process using dummy wafers for a certain period of time to enhance its performance. After the break-in process, the main Si wafer polishing process must be performed. In this study, the characteristics of break-in process were investigated in Si wafer polishing. Viscoelastic behavior, temperature variation of pad and friction were measured to evaluate the break-in phenomenon. Also, it is found that the characteristic of the break-in seems to be related to viscoelastic behavior of pad.

• Steel and Composite Structures
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• v.18 no.6
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• pp.1465-1478
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• 2015

The effect of cutting off fibers on transient load in a polymeric matrix composite lamina was studied in this paper. The behavior of fibers was considered to be linear elastic and the matrix behavior was considered to be linear viscoelastic. To model the viscoelastic behavior of matrix, a three parameter solid model was employed. To conduct this research, finite difference method was used. The governing equations were obtained using Shear-lag theory and were solved using boundary and initial conditions before and after the development of break. Using finite difference method, the governing integro-differential equations were developed and normal stress in the fibers is obtained. Particular attention is paid the dynamic overshoot resulting when the fibers are suddenly broken. Results show that considering viscoelastic properties of matrix causes a decrease in dynamic load concentration factor and an increase in static load concentration factor. Also with increases the number of broken fibers, trend of increasing load concentration factor decreases gradually. Furthermore, the overshoot of load in fibers adjacent to the break in a polymeric matrix with high transient time is lower than a matrix with lower transient time, but the load concentration factor in the matrix with high transient time is lower.

• Nuclear Engineering and Technology
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• v.49 no.5
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• pp.968-978
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• 2017

Three small-break loss-of-coolant accident (SBLOCA) tests with safety injection pumps were carried out using the integral-effect test loop for SMART (System-integrated Modular Advanced ReacTor), i.e., the SMART-ITL facility. The types of break are a safety injection system line break, shutdown cooling system line break, and pressurizer safety valve line break. The thermal-hydraulic phenomena show a traditional behavior to decrease the temperature and pressure whereas the local phenomena are slightly different during the early stage of the transient after a break simulation. A safety injection using a high-pressure pump effectively cools down and recovers the inventory of a reactor coolant system. The global trends show reproducible results for an SBLOCA scenario with three different break locations. It was confirmed that the safety injection system is robustly safe enough to protect from a core uncovery.

• Nuclear Engineering and Technology
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• v.50 no.5
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• pp.758-766
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• 2018

We developed numerical models to efficiently simulate the low-cycle fatigue behavior of a pipe elbow. To verify the model, in-plane cyclic bending tests of pipe elbow specimens were conducted, and a through crack occurred in the vicinity of the crown. Numerical models based on the erosion method and tie-break method are developed, and the numerical results are compared with experimental results. The calculated results of both models are in good agreement with experimental results, and the model using the tie-break method possesses two times faster calculation speed. Therefore, the numerical model based on the tie-break method would be beneficial to evaluate the strength of piping systems under seismic loadings.

• Nuclear Engineering and Technology
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• v.44 no.7
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• pp.719-726
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• 2012

The object of this work is the validation and assessment of the TRACE v5.0 code using the scaled test ATLAS1 facility in the context of a DVI2 line break. In particular, the experiment selected models the 50%, 6-inch break of a DVI line. The same experiment was also adopted as a reference test in the ISP-503. The ISP-50 was proposed to, and accepted by, the OECD/NEA/CSNI due to its technical importance in the development of a best-estimate of safety analysis methodology for DVI line break accidents. In particular, the behavior of the two-phase flow in the upper annulus downcomer was expected to be complicated. What resulted was the need for relevant models to be implemented into safety analysis codes, in order to predict these thermal hydraulic phenomena correctly.

• Journal of Korea Water Resources Association
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• v.41 no.7
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• pp.669-679
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• 2008

The present study examines similarity of behavior between an overtopping wave generated by a plunging wave and a dam-break flow through hydraulic model tests. The dam-break flow has been employed to estimate the overtopping effect on the basis of the dam-break flow's behavior similar to the overtopping. In this study, the overtopping velocity was measured by a modified image technique using bubble and bubble texture images called bubble image velocitmetry. From the measurements, the vertical profiles of horizontal overtopping velocity at cross-sections along the deck were presented and discussed. Maximum velocity and depth-averaged velocity at each cross-section were compared with an analytical solution solving the dam-break flow, Ritter's solution. The initial water depth of importance for the solution was determined from the tested wave condition and the overtopping measurements. The comparison shows that the solution with the initial water depth estimated using the front velocity of the overtopping wave is in good agreements with the measurements.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.725-730
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• 2010

The leak-before-break behavior and the crack opening displacement were investigated of statically indeterminate piping system and statically determinate piping system after a crack penetration. The reduction in the ultimate strength caused by a crack was relatively small in the statically indeterminate piping system. The leak-before-break in the statically indeterminate piping system had a larger safety margin than that in the statically determinate piping system. The crack opening displacement after crack penetration in a pipe with a nonpenetrating crack was evaluated by using a plastic rotation angle.