• Title/Summary/Keyword: Void Removal

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ROLE OF PASSIVE SAFETY FEATURES IN PREVENTION AND MITIGATION OF SEVERE PLANT CONDITIONS IN INDIAN ADVANCED HEAVY WATER REACTOR

  • Jain, Vikas;Nayak, A.K.;Dhiman, M.;Kulkarni, P.P.;Vijayan, P.K.;Vaze, K.K.
    • Nuclear Engineering and Technology
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    • v.45 no.5
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    • pp.625-636
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    • 2013
  • Pressing demands of economic competitiveness, the need for large-scale deployment, minimizing the need of human intervention, and experience from the past events and incidents at operating reactors have guided the evolution and innovations in reactor technologies. Indian innovative reactor 'AHWR' is a pressure-tube type natural circulation based boiling water reactor that is designed to meet such requirements, which essentially reflect the needs of next generation reactors. The reactor employs various passive features to prevent and mitigate accidental conditions, like a slightly negative void reactivity coefficient, passive poison injection to scram the reactor in event of failure of the wired shutdown systems, a large elevated pool of water as a heat sink inside the containment, passive decay heat removal based on natural circulation and passive valves, passive ECC injection, etc. It is designed to meet the fundamental safety requirements of safe shutdown, safe decay heat removal and confinement of activity with no impact in public domain, and hence, no need for emergency planning under all conceivable scenarios. This paper examines the role of the various passive safety systems in prevention and mitigation of severe plant conditions that may arise in event of multiple failures. For the purpose of demonstration of the effectiveness of its passive features, postulated scenarios on the lines of three major severe accidents in the history of nuclear power reactors are considered, namely; the Three Mile Island (TMI), Chernobyl and Fukushima accidents. Severe plant conditions along the lines of these scenarios are postulated to the extent conceivable in the reactor under consideration and analyzed using best estimate system thermal-hydraulics code RELAP5/Mod3.2. It is found that the various passive systems incorporated enable the reactor to tolerate the postulated accident conditions without causing severe plant conditions and core degradation.

A Study on Properties of Sound Absorbing Materials with Characteristics of Exhaust-gas Purge (배기가스를 정화하는 흡음재의 특성에 관한 연구)

  • 이승한;황보광수;장석수
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.05a
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    • pp.935-940
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    • 2001
  • This study search for absorbing sound and exhaust-gas which aims to manufacture continuous void by using clay and foam, the surface of materials is covered with $TiO_{2}$ powder as heat treatment. According to the results of the experiment, the increase of thickness of manufactured sound absorbing materials caused the increase of absorption rate in the range of low and middle sound and thus it can be an important factor of improving absorption rate. Sound absorbing materials could satisfy 70% of the average of sound absorption ratio in 7cm thickness. Also, the manufactured sound absorbing materials is covered with $TiO_{2}$ showed an excellency in the clarification of exhaust-gas under ultraviolet rays treatment when 70% of removal rate and about 10% of generation rate of $NO_{2}$ is settled by the flow of 2 $\ell$/min NO gas. Especially, manufactured sound absorbing materials could improve compressive strength of continuos porous concrete. in the case of 7% bubble addition, when the substitution rate of coagulator was 30% and 20%, compressive strength was 45kgf/$cm^{2}$ and 65kgf/$cm^{2}$ respectively. As the substitution rate of coagulator reducing, compressive strength increased after preforming burnt clay.

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Capillary-driven Rigiflex Lithography for Fabricating High Aspect-Ratio Polymer Nanostructures (모세관 리소그라피를 이용한 고종횡비 나노구조 형성법)

  • Jeong, Hoon-Eui;Lee, Sung-Hoon;Kim, Pil-Nam;Suh, Kahp-Y.
    • Journal of the Korean Society of Visualization
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    • v.5 no.1
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    • pp.3-8
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    • 2007
  • We present simple methods for fabricating high aspect-ratio polymer nanostructures on a solid substrate by rigiflex lithography with tailored capillarity and adhesive force. In the first method, a thin, thermoplastic polymer film was prepared by spin coating on a substrate and the temperature was raised above the polymer's glass transition temperature ($T_g$) while in conformal contact with a poly(urethane acrylate) (PUA) mold having nano-cavities. Consequently, capillarity forces the polymer film to rise into the void space of the mold, resulting in nanostructures with an aspect ratio of ${\sim}4$. In the second method, very high aspect-ratio (>20) nanohairs were fabricated by elongating the pre-formed nanostructures upon removal of the mold with the aid of tailored capillarity and adhesive force at the mold/polymer interface. Finally, these two methods were further used to fabricate micro/nano hierarchical structures by sequential application of the molding process for mimicking nature's functional surfaces such as a lotus leaf and gecko foot hairs.

Analysis of Partial Discharge in High Voltage Motor Model Coils (고압전동기 모델 코일에서 부분방전 분석)

  • Kim, Hee-Dong
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.55 no.4
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    • pp.178-182
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    • 2006
  • Five model coils of 6.6 kV motor were manufactured with several defects. These stator coils have artificial defects such as void of groundwall insulation, removal of semi-conductive coating and damage of strand insulation. Epoxy-mica coupler(80 pF) was connected to five model coil terminals. The voltage applied to the coils was 3.81 kV, 4.76 kV, 6.0 kV and 6.6 kV, respectively. Partial discharge(PD) tests performed in the laboratory and shield room. Digital PD detector(PDD) and turbine generator analyzer(TGA) were used to measure PD activity. TGA summarizes each plot with two quantities such as the normalized quantity number(NQN) and the peak PD magnitude(Qm). The PD levels in pC were measured with PDD. PD patterns of model coils were indicated the internal and slot discharges. PD patterns are consistent with the result of measurement using PDD and TGA instruments. AC breakdown test was performed on five model coils in order to confirm the result of PD measurements. All the failures were located in a line-end coil at the exit from the core slot.

GROUND TREATMENT CASE HISTORY OFR SOFT CLAY LAYER AND EVALUATION OF ITS IMPROVEMENT (연약지반처리와 개량효과 평가사례)

  • Lee, Yeong-Nam;Lee, Hyeong-Ju;Sim, Dong-Hyeon
    • Proceedings of the Korean Geotechical Society Conference
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    • 1992.10a
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    • pp.113-120
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    • 1992
  • The construction of container terminal at Brani, Singapore required the improvement of soft clay layer having the thickness of about 6.5m, average moisture content of 79.4%, liquid limit of 90.4%, plastic limit of 21.8%, field vane strength of 10 to 25 KPa, pre-consolidation pressure of 225 to 60 KPa and compression index of 0.4 to 1.0. For the improvement of this layer, Colbon drains of 1.3m spacing in triangular pattern were installed to the bottom of the layer and surcharge of more than 11.25m high sand fill was later applied to the treated area. The settlement and lateral displacement of the ground were measured and the speed of surcharge filling was controlled, based on these readings. The removal of surcharge was determinied using the estimated time for the 90% degree of consolidation under the design pressure of 180KPa. The field and laboratory test results show that the soft clay layer has been improved substantially in its strength and consolidation characteristics: increase in strength of about 50KPa and pre-consolidation pressure and decrease in void ratio and compression index.

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Flow Characteristics Analysis for the Chemical Decontamination of the Kori-1 Nuclear Power Plant

  • Cho, Seo-Yeon;Kim, ByongSup;Bang, Youngsuk;Kim, KeonYeop
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.19 no.1
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    • pp.51-58
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    • 2021
  • Chemical decontamination of primary systems in a nuclear power plant (NPP) prior to commencing the main decommissioning activities is required to reduce radiation exposure during its process. The entire process is repeated until the desired decontamination factor is obtained. To achieve improved decontamination factors over a shorter time with fewer cycles, the appropriate flow characteristics are required. In addition, to prepare an operating procedure that is adaptable to various conditions and situations, the transient analysis results would be required for operator action and system impact assessment. In this study, the flow characteristics in the steady-state and transient conditions for the chemical decontamination operations of the Kori-1 NPP were analyzed and compared via the MARS-KS code simulation. Loss of residual heat removal (RHR) and steam generator tube rupture (SGTR) simulations were conducted for the postulated abnormal events. Loss of RHR results showed the reactor coolant system (RCS) temperature increase, which can damage the reactor coolant pump (RCP)s by its cavitation. The SGTR results indicated a void formation in the RCS interior by the decrease in pressurizer (PZR) pressure, which can cause surface exposure and tripping of the RCPs unless proper actions are taken before the required pressure limit is achieved.

A New Proposed Technique for a Secondary Consolidation Coefficient Based on the Constant Rate of Strain Test (CRS시험에 의한 2차압밀계수의 결정방법 제안)

  • 김형주;이민선;이용주;김대우
    • Journal of the Korean Geotechnical Society
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    • v.20 no.8
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    • pp.113-121
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    • 2004
  • The present study is suggested to estimate the degree of secondary consolidation caused by various changes of stress such as loading, unloading and reloading in improving poor subsoil through pre-compression loading construction method and, for this purpose, examined the characteristics of the consolidation of Kunsan clay through incremental loading test (IL) using standard consolidation tester and constant loading rate test (CLR), which were adapted from the constant rate of strain test (CRS). In addition, after CRS test, this study determined the characteristics of secondary consolidation and relationships among void ratio, effective stress and time according to the ratio of effective over-consolidation on reloading at the point of time of random expansion. Kunsan clay had larger expansion and smaller secondary consolidation settlement when the ratio of effective over-consolidation was high. In addition, when loading was applied after the load was removed at once, the secondary consolidation coefficient $C'_{\alpha}$ was smaller than that when the load was removed gradually, and when the ratio of effective over-consolidation was over 1.4 a similar value was produced. Based on the entire settlement resulting from reloading, the secondary consolidation coefficient $C"_{\alpha}$ increased non-linearly with the lapse of time but the final value was similar to that in the case of rapid removal. The strain velocity of void ratio was in a regular linear relationship with the increase of loading time regardless of the ratio of effective over-consolidation in both tests and it grew smaller with the increase of the ratio of effective over-consolidation.tion.

An Overview of Coal Mine Drainage Treatment (석탄광의 광산배수처리기술 현황 및 전망)

  • 정영욱
    • Economic and Environmental Geology
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    • v.37 no.1
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    • pp.107-111
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    • 2004
  • This study was undertaken to summarize of the efficiencies of the passive treatment system and suggest future studies for the solution of mine drainage problem. Flow rates of mine drainage from the abandoned coal mines are about 80,000 ton/day. Contaminated mine drainages over about 50 ton/day of flow rate were treated by passive treatment facilities such as Successive Alkalinity Producing Systems(SAPS), oxidation pond and oxic wetland. Chemical analysis for 13 passive coal mine treatment facilities showed that SAPS was the core of treatment facilities because the variation of Fe removal rates was relatively smaller than any other processes and re-leaching of Fe was not measured. The performance and life of SAPS depended on decrease in permeability and retention time due to accumulation of sludge. It is inferred that upgrade of design of the passive treatment system and in-situ treatment using underground void will be necessary for the amelioration of the mine drainage with high metal loading rates.

Predictors of Acute Postoperative Urinary Retention after Transvaginal Uterosacral Suspension Surgery

  • Son, Eun-Joo;Joo, Eunwook;Hwang, Woo Yeon;Kang, Mi Hyun;Choi, Hyun Jin;Yoo, Eun-Hee
    • Journal of Menopausal Medicine
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    • v.24 no.3
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    • pp.163-168
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    • 2018
  • Objectives: To investigate the rate of postoperative urinary retention (POUR) and identify the risk factors for this complication in women who underwent transvaginal uterosacral suspension surgery. Methods: A retrospective chart review was conducted for 75 women who underwent transvaginal uterosacral suspension surgery with vaginal hysterectomy, repair of cystocele, and levator myorrhaphy with/without transobturator anti-incontinence surgery. POUR was defined as a need for continuous intermittent catheterization on the third day subsequent to removal of the urethral indwelling catheter. Results: Acute POUR was reported in 18 women (24.0%). Thirty-six of the 75 patients (48.0%) had undergone anti-incontinence surgery. Crude analysis revealed significant association between the following variables and the risk of POUR: hypertension, the lower average flow rate in the pressure-flow study (PFS), greater post-void residual (PVR) urine volume in PFS, and PVR >30% of the total bladder capacity (TBC) in PFS. In the logistic regression analysis, PVR >30% of the TBC in PFS was identified as the only significant predictor of POUR (odds ratio, 15.4; 95% confidence interval, 2.5-90.9; P = 0.003). Conclusions: The PVR >30% of the TBC in PFS was identified as the only predictive factor of acute POUR in women who underwent transvaginal uterosacral suspension surgery.

Analysis on Hypothetical Multiple Events of mSGTR and SBO at CANDU-6 Plants Using MARS-KS Code (중수로 원전 가상의 mSGTR과 SBO 다중 사건에 대한 MARS-KS 코드 분석)

  • Seon Oh YU;Kyung Won LEE;Kyung Lok BAEK;Manwoong KIM
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.17 no.1
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    • pp.18-27
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    • 2021
  • This study aims to develop an improved evaluation technology for assessing CANDU-6 safety. For this purpose, the multiple steam generator tube rupture (mSGTR) followed by an unmitigated station blackout (SBO) in a CANDU-6 plant was selected as a hypothetical event scenario and the analysis model to evaluate the plant responses was envisioned into the MARS-KS input model. The model includes logic models for controlling the pressure and inventory of the primary heat transport system (PHTS) decreasing due to the u-tubes' rupture, as well as the main features of PHTS with a simplified model for the horizontal fuel channels, the secondary heat transport system including the shell side of steam generators, feedwater and main steam line, and moderator system. A steady state condition was successfully achieved to confirm the stable convergence of the key parameters. Until the turbine trip, the fuel channels were adequately cooled by forced circulation of coolant and supply of main feedwater. However, due to the continuous reduction of PHTS pressure and inventory, the reactor and turbine were shut down and the thermal-hydraulic behaviors between intact and broken loops got asymmetric. Furthermore, as the conditions of low-flow coolant and high void fraction in the broken loop persisted, leading to degradation of decay heat removal, it was evaluated that the peak cladding temperature (PCT) exceeded the limit criteria for ensuring nuclear fuel integrity. This study is expected to provide the technical bases to the accident management strategy for transient conditions with multiple events.