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Analysis of hot leg natural circulation under station blackout severe accident

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Nuclear Science and Techniques 2007年第2期18卷 123-128页

作者： DENG Jian CAO xuewu School of Nuclear Science and Engineering Shanghai Jiaotong University Shanghai 200240 China

Under severe accidents, natural circulation flows are important to influence the accident progression and result in a pressurized water reactor (PWR). In a station blackout accident with no recovery of steam generator (SG) auxiliary feedwater (TMLB' severe accident scenario), the hot leg countercurrent natural circulation flow is analyzed by using a severe-accident code, to better understand its potential impacts on the creep-rupture timing among the surge line, the hot leg, and SG tubes. The results show that the natural circulation may delay the failure time of the hot leg. The recirculation ratio and the hot mixing factor are also calculated and discussed.

关键词：压水堆全场断电严重事故热管段自然循环

Particle flux through the Huanghai Sea cold water mass

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Acta Oceanologica Sinica 2005年第5期24卷 78-88页

作者： GUO xuewu ZHANG Yansong Yellow Sea Fisheries Research Institute Chinese Academy of Fishery Sciences Qingdao 266071 China Jiaozhou Environmental Protection Bureau Jiaozhou 266300 China

Settling particulate matter （SPM） was collected by using sediment traps at four stations in a survey section from Qingdao to Cheju-do, across the Huanghai Sea cold water mass （HSCWM）, in August 2002. The sediment traps were planted in three layers： the upper layer of the thermocline （ULT） above the HSCWM, the lower layer of the thermocline （LLT）, and the bottom layer of water column （BL）. To determine the particle flux, the contents of organic carbon （POC）, organic nitrogen （PON）, total carbon （PC）, and total phosphorous （PP） in SPM were analyzed, and two flux models （Ⅰ and Ⅱ） were improved to calculate the resuspension ratio, with an assumption in Model Ⅰ that the vertical flux of SPM in the LLT equals the net vertical flux of SPM in the whole water column. An X value, i.e., the fraction of the resuspension flux originating from the surficial sediments nearby the sampling station, was deduced from Model Ⅰ to estimate the contribution of lateral currents to the total resuspension flux. The results showed that inorganic particles, fecal pellets, and miscellaneous aggregates were the major types of SPM in the HSCWM, and the contents of POC, PON, PC, and PP all decreased with water depth. A great deal of fecal pellets found in the LLT indicates that the main space producing biogenic SPM is the thermocline, and especially the LLT, where the C/N ratio is lower than that in the ULT. The resuspension ratios, 90%-96% among stations, imply strong impact ofresuspension on particle flux in the BL. These values were not significantly different between the two flux models, suggesting that the hypothesis in Model Ⅰ that the flux in the LLT equaling the net flux to the bottom is acceptable for shallow waters with stratification like the HSCWM. The POC export ratio from the HSCWM ranges from 35% to 68%. It benefits from the short sinking distance in shallow water. The upwelling in the HSCWM enhanced the POC flux through the water mass, and the lateral currents provides up to being

关键词： settling particulate matter particle flux model resuspension ratio thermocline Huanghai Sea Cold Water Mass

Simulation of cavitation in rotary valve of hydraulic power steering gear

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Science China(Technological Sciences) 2009年第11期52卷 3142-3148页

作者： LIU YaHui JI xuewu Department of Automotive Engineering Tsinghua UniversityBeijing 100084

Hydraulic power steering gear supplies assistant power by liquid stream. The stream will be changed greatly for the flow field formed by the rotary valve will vary during steering. And the change of the stream in this narrow field will (be big enough to) cause the fluctuation of the assistance power and noise of the steering gear. 3-D meshes of the flow field between the sleeve and the rotor of the valve with different structure parameters such as entry caliber and groove depth were set up and a general CFD code-Fluent was used to analyze the stream performance. The results including pressure and gas-phase's volume fraction were analyzed under certain operation flow rate. It was found that the entry caliber did not affect the operation pressure of the valve under the same flow rate but affected the gas-phase's volume fraction of the flow field, and so did the groove depth of the valve' sleeve and rotor. Many researches have pointed that the noise of steering valve is almost cavitation noise, that is, the gas-phase in the flow field has great correlation with rotary valve noise. Based on these analyses of the stream in the rotary steering valve, this paper gave suggestion that increasing entry caliber of the rotary valve and choosing appropriate groove depth will reduce the valve noise.

关键词： rotary valve computational fluid dynamic cavitation noise

Methodology for reliability allocation based on fault tree analysis and dualistic contrast

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Nuclear Science and Techniques 2008年第4期19卷 251-256页

作者： TONG Lili CAO xuewu School of Nuclear Science and Engineering Shanghai Jiao Tong University Shanghai200240 China

Reliability allocation is a difficult multi-objective optimization problem. This paper presents a methodology for reliability allocation that can be applied to determine the reliability characteristics of reactor systems or subsystems. The dualistic contrast,known as one of the most powerful tools for optimization problems,is applied to the reliability allocation model of a typical system in this article. And the fault tree analysis,deemed to be one of the effective methods of reliability analysis,is also adopted. Thus a failure rate allocation model based on the fault tree analysis and dualistic contrast is achieved. An application on the emergency diesel generator in the nuclear power plant is given to illustrate the proposed method.

关键词：反应堆安全事故维修方法核技术

Effect of water injection on hydrogen generation during severe accident in PWR

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Nuclear Science and Techniques 2009年第5期20卷 312-316页

作者： TAO Jun CAO xuewu School of Mechanical and Power Engineering Shanghai Jiao Tong University Shanghai 200240 China

Effect of water injection on hydrogen generation during severe accident in a 1000 MWe pressurized water reactor was studied. The analyses were carried out with different water injection rates at different core damage stages. The core can be quenched and accident progression can be terminated by water injection at the time before cohesive core debris is formed at lower core region. Hydrogen generation rate decreases with water injection into the core at the peak core temperature of 1700 K, because the core is quenched and reflooded quickly. The water injection at the peak core temperature of 1900 K, the hydrogen generation rate increases at low injection rates of the water, as the core is quenched slowly and the core remains in uncovered condition at high temperatures for a longer time than the situation of high injection rate. At peak core temperature of 2100–2300 K, the Hydrogen generation rate increases by water injection because of the steam serving to the high temperature steam-starved core. Hydrogen generation rate increases significantly after water injection into the core at peak core temperature of 2500 K because of the steam serving to the relocating Zr-U-O mixture. Almost no hydrogen generation can be seen in base case after formation of the molten pool at the lower core region. However, hydrogen is generated if water is injected into the molten pool, because steam serves to the crust supporting the molten pool. Reactor coolant system (RCS) depressurization by opening power operated relief valves has important effect on hydrogen generation. Special attention should be paid to hydrogen generation enhancement caused by RCS depressurization.

关键词： PWR 核技术研究发展 RCS

Hydrogen and steam distribution following a small-break LOCA in large dry containment

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Nuclear Science and Techniques 2007年第3期18卷 181-185页

作者： DENG Jian CAO xuewu School of Nuclear Science and Engineering Shanghai Jiaotong University Shanghai 200240 China

The hydrogen deflagration is one of the major risk contributors to threaten the integrity of the containment in a nuclear power plant, and hydrogen control in the case of severe accidents is required by nuclear regulations. Based on the large dry containment model developed with the integral severe-accident analysis tool, a small-break loss-of-coolant-accident (LOCA) without HPI, LPI, AFW and containment sprays, leading to the core degradation and large hydrogen generation, is calculated. Hydrogen and steam distribution in containment compartments is investi- gated. The analysis results show that significant hydrogen deflagration risk exits in the reactor coolant pump (RCP) compartment and the cavity during the early period, if no actions are taken to mitigate the effects of hydrogen accu- mulation.

关键词：氢蒸发严重事故氢分布小破口事故

Simulation of the mixing process in FCIs with hydrodynamic fragmentation model

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Nuclear Science and Techniques 2007年第4期18卷 242-246页

作者： LIN Qian CAO xuewu School of Nuclear Science and Engineering Shanghai Jiaotong University Shanghai 200240 China

Fuel Coolant Interactions (FCIs) are important issues in nuclear reactor severe accident analysis. In FCIs, fragmentation model of molten droplets is a key factor to estimate degree of possible damage. In this paper, the mixing process in FCIs is studied by the simulation of MIXA experiment with hydrodynamic fragmentation model. The result shows that hydrodynamic fragmentation model underestimates the fragmentation rate of high temperature molten droplets under the condition of low Weber numbers. It is concluded that models based on thermal fragmentation mechanism should be adopted to analyze the FCI process and its consequence.

关键词：核反应堆燃料冷冻作用事故燃料熔化

Microstructures and electrochemical behaviors of casting magnesium alloys with enhanced compression strengths and decomposition rates

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Journal of Magnesium and Alloys 2023年第4期11卷 1213-1223页

作者： xuewu Li Qingyuan Yu Xi Chen Qiaoxin Zhang State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China School of Mechanical Engineering Xi’an University of Science and Technology58 Yanta RoadXi’an 710054China School of Mechanical and Electronic Engineering Wuhan University of Technology122 Luoshi RoadWuhan 430070China

New-type magnesium alloy with prominent solubility and mechanical property lays foundation for preparing fracturing part in petroleum ***,Mg-xZn-Zr-SiC alloy is prepared with casting *** and compression tests are conducted to assess the feasibility as decomposable ***,composition,phase and distribution are characterized to investigate decomposition *** indicate that floccule,substrate component and reticulate secondary phase are formed on as-prepared *** also acts out enhanced compression strength to maintain pressure and guarantee stability in dissolution ***,as decomposition time and zinc content increase,couple corrosion intensifies,resulting in gradually enhanced decomposition *** sample decomposition is mainly due to basal anode dissolution,micro particle exfoliation and poor decomposition resistance of corroding *** work shows profound significance in preparing new-type accessible alloy to ensure rapid dissolution of fracturing part and guarantee stable compression strength in oil-gas reservoir exploitation.

关键词： Magnesium alloy Corrosion dissolution Compression strength Electrochemical test Decomposition mechanism

Simulation of quenching in horizontal geometry channel

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Nuclear Science and Techniques 2010年第6期21卷 370-374页

作者： Yuan Jingtian Tong Lili Cao xuewu Shanghai Jiao Tong Univ Sch Mech Engn Shanghai 200240 Peoples R China

Two tests of refilling and reflooding in the horizontal geometry channel under different pressure conditions,respectively,are conducted to understand the thermal hydraulics behavior during a LOCA in the CANDU *** case of refilling a hot horizontal tube test and four cases of reflooding a horizontal fuel channel test series (35%and 60%break size of reactor inlet header with single-end injection or both-end injection,respectively) have been *** horizontal channel is simulated with the model splitting as parallel pipes with cross flow junction *** simulation results have been compared with the tests in terms of wall temperature or heated-pin surface *** results are reasonably acceptable and it shows that the code is applicable on horizontal channel quenching.

关键词：水平测试通道测试模型模拟几何淬火 CANDU堆压力条件热工水力