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        Comparative Experiments to Assess the Effects of Accumulator Nitrogen Injection on Passive Core Cooling During Small Break LOCA

        Li Yuquan,Hao Botao,Zhong Jia,Wang Nan 한국원자력학회 2017 Nuclear Engineering and Technology Vol.49 No.1

        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 facilitydthe advanced core-cooling mechanism experiment (ACME)dwas 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 groupsda 2-inch cold leg break and a double-ended direct-vessel-injection (DEDVI) line breakdwere 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.

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        Recent Changes in Heavy Precipitation Events in Northern Central China and Associated Atmospheric Circulation

        Tingting Han,Xinyi Guo,Botao Zhou,Xin Hao 한국기상학회 2021 Asia-Pacific Journal of Atmospheric Sciences Vol.57 No.2

        Northern Central China (NC China) is a seriously arid region. Precipitation variations are vital for environmental protection and socio-economical development. This study investigates the recent changes in summer heavy precipitation (HP) events over NC China and associated atmospheric circulation anomalies. Compared with the period of 1986–2002, the HP amount and frequency both significantly increase during 2003–2016, contributing to the shift to increase in total summer precipitation amount. After the early 2000s, the Northwest Pacific subtropical high becomes intensified and shifts westward and northward, leading to significant moisture convergence anomalies over NC China and divergence anomalies over Northwest Pacific. Therefore, the net moisture budget dramatically increases since the early 2000s. Further results show that the strengthened net moisture influx across the southern boundary contributes dominantly to the increased net moisture budget, especially at the lower level. Despite a relatively small magnitude, the intensified westerly current across western boundary makes a dominant contribution at middle and upper layers. Additionally, the strengthened westerly and easterly anomalies occupy northern and southern China, respectively, along with the eastward expansion of westerly jet stream region. Thus, the lower-level convergence and upper-level divergence both intensify, and further trigger enhanced ascending movement. These conditions jointly contribute to the inter-decadal change in HP events over NC China after the early 2000s.

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