• Nuclear Engineering and Technology
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• v.49 no.1
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• pp.54-70
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• 2017

The accumulator is a passive safety injection device for emergency core cooling systems. As an important safety feature for providing a high-speed injection flow to the core by compressed nitrogen gas pressure during a loss-of-coolant accident (LOCA), the accumulator injects its precharged nitrogen into the system after its coolant has been emptied. Attention has been drawn to the possible negative effects caused by such a nitrogen injection in passive safety nuclear power plants. Although some experimental work on the nitrogen injection has been done, there have been no comparative tests in which the effects on the system responses and the core safety have been clearly assessed. In this study, a new thermal hydraulic integral test facility-the advanced core-cooling mechanism experiment (ACME)-was designed and constructed to support the CAP1400 safety review. The ACME test facility was used to study the nitrogen injection effects on the system responses to the small break loss-of-coolant accident LOCA (SBLOCA) transient. Two comparison test groups-a 2-inch cold leg break and a double-ended direct-vessel-injection (DEDVI) line break-were conducted. Each group consists of a nitrogen injection test and a nitrogen isolation comparison test with the same break conditions. To assess the nitrogen injection effects, the experimental data that are representative of the system responses and the core safety were compared and analyzed. The results of the comparison show that the effects of nitrogen injection on system responses and core safety are significantly different between the 2-inch and DEDVI breaks. The mechanisms of the different effects on the transient were also investigated. The amount of nitrogen injected, along with its heat absorption, was likewise evaluated in order to assess its effect on the system depressurization process. The results of the comparison and analyses in this study are important for recognizing and understanding the potential negative effects on the passive core cooling performance caused by nitrogen injection during the SBLOCA transient.

• Communications for Statistical Applications and Methods
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• v.24 no.4
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• pp.367-382
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• 2017

We consider an infinite-order long-memory heterogeneous autoregressive (HAR) model, which is motivated by a long-memory property of realized volatilities (RVs), as an extension of the finite order HAR-RV model. We develop bootstrap tests for structural mean or variance changes in the infinite-order HAR model via stationary bootstrapping. A functional central limit theorem is proved for stationary bootstrap sample, which enables us to develop stationary bootstrap cumulative sum (CUSUM) tests: a bootstrap test for mean break and a bootstrap test for variance break. Consistencies of the bootstrap null distributions of the CUSUM tests are proved. Consistencies of the bootstrap CUSUM tests are also proved under alternative hypotheses of mean or variance changes. A Monte-Carlo simulation shows that stationary bootstrapping improves the sizes of existing tests.

• Journal of Environmental Science International
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• v.28 no.2
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• pp.211-217
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• 2019

A Numerical modeling approach is usually applied to reproduce the physical phenomena of a fill dam-break. The accuracy of the dam-break model depends on the physical structure that defines input variables such as the storage volume, breach formation and progress, and the parameters of the model, which are subjective as they are prescribed by users. In this study, a sensitivity analysis was performed for the nonlinear breach progression curve that was already developed, which includes four parameters. The study focuses on the two of the parameters which control the breach forming time and peak discharge. The model is coupled with a two-dimensional flood simulation model (FLO-2D) to examine flood coverage and depth. It is generally observed that the parameter ${\beta}$ controls only the breach forming time, the parameter ${\gamma}$ is particularly sensitive to the peak flow.

• Journal of Technologic Dentistry
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• v.34 no.2
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• pp.95-103
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• 2012

Purpose: Fracture strength of all-ceramic 3-unit fixed partial dentures manufactured by CAD/CAM and copy-milling systems were evaluated. Methods: Zirconia cores were made by milling the pre-sintered zirconia block by CAD/CAM or copy milling method followed by subsequent sintering. By building-up the corresponding porcelains on the core, all-ceramic bridges were fabricated, and those were evaluated in comparison with PFM fixed partial denture. Results: During the flexural test of the 3-unit PFM bridge, the porcelain started to chip or break at 507.28(${\pm}62.82$)kgf and the metal framework did not break until the maximum load level of 800kgf which was set in the testing instrument of this study. However, among all-ceramic restoration test groups, Everest(EV) group showed a peeling off or breakage of the porcelain from 365.64(${\pm}64.96$)kgf and the core was broken at 491.77(${\pm}55.62$)kgf. Those values of Zirkonzahn(ZR) were 431.03(${\pm}58.47$)kgf and 602.74(${\pm}48.44$)kgf, respectively. The break strength of the porcelain of PFM(PM) group was significantly higher than that of EV (p<0.05) group and there was no significant difference when comparing to that of ZR (p>0.05). ZR group showed higher break strength than that of EV group however there was no significant difference (p>0.05). The break strength of cores were in the increasing order of EV < ZR < PM (p<0.05). Conclusion: We could find that even though the PM group fractured at much higher value than all-ceramic cores, the breakage values of the porcelain of PM group with crack formation or delamination, which will be regarded as clinical failure, was significantly higher than that of EV group and not significantly higher than that of ZR group at p-values of 0.05. The break strength of ZR group was higher than that of EV group at an insignificant level(p>0.05).

• The Journal of Engineering Geology
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• v.24 no.1
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• pp.53-67
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• 2014

Numerical modeling is commonly used to reproduce the physical phenomena of dam-break and to compile resulting flood hazard maps. The accuracy of a dam-break model depends on the physical structure that describes the volume of storage, breach formation and progress, input variables, and model parameters. Model input and parameters are subjective in that they are prescribed; hence, caution is needed when interpreting the results. This study focuses on three parameters (breach degree ${\theta}$, shape factor P, and collapse rate k) used when the dam-break model is coupled with FLO-2D (a two-dimensional flood simulation model) to estimate flood coverage and depth etc. The results show that the simulation is sensitive to the shape factor P and the collapse rate k but not to the breach degree ${\theta}$. This study will contribute to reducing flood damage from dam-break disasters in the future.

• Korean Journal of Hydrosciences
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• v.1
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• pp.27-38
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• 1990

Three representative dam-break models, HEC-1, DAMBRK, and SMPDBK were analyzed respectively in their theories and then applied to the failure of Teton Dam for which some observed data exist. From the results of this study, it can be concluded that:(1)HEC-1, which uses the hydrologic routing method, produces stable solutions for almost all the cases that were tested in this study :(2)DAMBRK, which uses the dynamic routing method, is most accurate among the three models ;(3)SMPDBK, which uses the generalized dyanmic routing relationships, is most economical and easily applicable.

• Journal of agriculture & life science
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• v.52 no.6
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• pp.139-153
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• 2018

This study analyzes the economic effect of rehabilitation and upgrading of reservoirs as a prevented method against natural disasters under recent abnormal weather conditions and dam-break. For the analysis, we divide the purpose of rehabilitation and upgrading of reservoirs into the stable supply of rural water under uncertain weather conditions and the prevention of collapse due to the aging of the reservoir. We measure the economic effect of rehabilitation and upgrading of reservoirs by estimating the resident's willingness-to-pay for the project through Contingent Valuation Method(CVM). The result shows that distributions of willingness-to-pay to prevent natural disasters and dam-break are similar to each other. About 66% of the residents in sample regions are willing to pay for the project. The resident's willingness-to-pay to protect natural disasters and dam-break are 32,250 to 46,147 won and 28,427 to 47,308 won respectively on average for all sample regions. The comparison of willingness-to-pay by type of regions shows that paddy field areas are the highest followed by facility cultivation areas and urban areas. In addition, total expected value of the projects calculated based on the resident's willingness-to-pay for paddy field areas and facility cultivation areas are much larger than actual project costs. This implies that rural residents are fully aware of the importance of the project to prevent natural disasters and dam-break and are willing to pay for additional costs if needed.

• Nuclear Engineering and Technology
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• v.41 no.5
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• pp.691-708
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• 2009

In order to analyze thermal hydraulic phenomena during a DVI (Direct Vessel Injection) line break LOCA (Loss-of-Coolant Accident) in the APR1400 (Advanced Power Reactor 1400 MWe), we performed experimental studies with the SNUF (Seoul National University Facility), a reduced-height and reduce-pressure integral test loop with a scaled down APR1400. We performed experiments dealing with eight test cases under varied tests. As a result of the experiment, the primary system pressure, the coolant temperature, and the occurrence time of the downcomer seal clearing were affected significantly by the thermal power in the core and the SI flow rate. The break area played a dominant role in the vent of the steam. For our analytical investigation, we used the MARS code for simulation of the experiments to validate the calculation capability of the code. The results of the analysis showed good and sufficient agreement with the results of the experiment. However, the analysis revealed a weak capability in predicting the bypass flow of the SI water toward the broken DVI line, and it was insufficient to simulate the streamline contraction in the broken side. We, hence, need to improve the MARS code.

• Journal of architectural history
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• v.7 no.3 s.16
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• pp.137-149
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• 1998

The purpose of this study is to learn from a lesson of the historical fact, the Team 10's break away from the CIAM, which is selected as the most important event in the whole 20th century architecture by author as a historian. The CIAM, organized in 1928 by leading European architects in order to propose new architecture in the industrial era, expanded to the world, met almost annually with an idea of economic efficiency, new functional order, and industrial production for thirty years. Young architects had conflicted with old established group from 6th congress, and after 10th congress they met independently in 1959; the CIAM was disappeared and the Team 10 was born. Main issue of the break-away was human aspect. The Team 10 started from real man, concept of 'human contact', 'sense of community', and 'belonging' instead of abstract functional order. Although CIAM did not suggest inhumane architecture, their biological criteria with sunlight, air, sufficient site became physical determinism. Critique against the Team 10, unsuccess for making humane architecture leads to underestimation like a generational hegemony struggle. However, architect is not specialist of life but form. Historical reevaluation for Team 10 should be that they are the first group to raise an human issue in architecture. Success or not to solve the problem belongs to another domain. After 1960, modern architecture was attacked from the common people, not clients but 'users'. Academic circle tried to solve the problem with behavioral approach through a clear process, 'design method' and with phenomenological approach on real human experience. However practice became reactionary tendency, to make form a little complex, they became post-modern and deconstruction form. Failure of the Team 10's form proved that a complex form does not necessarily make a good life of people. In the Korean historic situation of colony ruling, confusion of liberation, and the War, we did not know the existence of both CIAM and Team 10. After 1970s' economic development, we have just copied Western form from Modern via Post-Modern to Deconstruction. If we make architecture people mattered, we should start from the basic, learning from the Team's break-away, instead of copying.

• The Journal of Engineering Geology
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• v.25 no.4
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• pp.449-458
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• 2015

The compilation of a flood hazard map is an efficient technique in managing areas at risk of flooding in the case of a dam-break. A scenario-based numerical modeling approach is commonly used to compile a flood hazard map related to dam-break and to determine the model parameters that capture peak discharge, including breach formation and progress, which are important in the modeling method. This approach might be considered less reliable if an existing model is used without local validation. In this study, a dam-break model is linked to a routing model to identify flood-risk areas in the case of failure of the Sandae Reservoir Gyeongju, Gyeongbuk. Model parameters are extracted from a DEM, and maps of land use and soil texture. The simulation results are compared with on-site investigations in terms of inundation and depth. The model reproduces the inundation zone with reasonable accuracy.