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《核科学与工程》2018,(6)
临界热流密度(CHF)是导致沸腾传热变化而使发热元件表面发生传热恶化的现象。RELAP5等系统程序的CHF模型对于传热系统的安全分析有重要影响。基于RELAP5程序对单棒及三棒束自然循环CHF实验进行建模,并在CHF实验数据基础上对RELAP5中CHF预测值进行对比分析。实验装置是带有一个向上流动通道的自然循环回路。其中单棒束加热测试段由一根轴向非均匀加热的电加热棒及圆管外壁组成的环管状流道,三棒束流道由三根相同的轴向非均匀加热棒与三叶型的外管组成。实验条件为低压、低流量的自然循环流动:入口压力110~270 kPa、入口过冷度为10~70 K、自然循环流量0~400 kg/(m2·s)。依次以质量流量、入口压力和过冷度为基准参数对比分析实验值和RELAP5预测值。结果表明在低压、低流量及自然循环条件下,RELAP5中的CHF预测值随着质量流量的增大而增大,与入口压力及过冷度之间的依赖关系不明显。通过对实验值与模型计算值的比较得到,单棒束RELAP5模型预测的CHF值偏高于实验值,而三棒束RELAP5模型的预测值较实验值偏低。 相似文献
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本文介绍高压高温水通过9根正方形排列的棒束及棒束定位架时的流动阻力特性实验研究.水强迫垂直向上流过棒束.分别进行了棒束不加热的单相流动实验和棒束均匀加热并出现汽液两相流动时的两相流动实验.单相及两相实验的参数范围:P=140公斤(力)/厘米~2,质量流速 ω~g=(1.5—8)×10~6公斤/米~2小时,雷诺数 Re=3×10~3—1.5×10~5,热流密度q=(0.2—1.3)×10~6千卡/米~2·小时,平均真实含汽量(?)=0.0002—0.23.在实验研究方法上,把欠热沸腾和饱和沸腾这两种工况都看成是两相流动工况,两种工况的实验数据用真实含汽量综合成统一的实验曲线和实验关系式.在测量技术方面,采用新设计的引压装置把压差信号从高压高温实验通道测孔处引入压差计.测取的信号可靠,测量误差小.实验数据全部用计算机处理.经过综合、分析、整理后,得到棒束摩阻实验曲线和实验关系式及定位架的形阻实验曲线. 相似文献
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以R-134a为模化工质,在内径为8 mm的圆管中进行了临界热流密度(CHF)实验研究。讨论了R-134a的CHF参数变化趋势,评价了Katto的流体模化方法。结果表明,CHF仅受局部参数影响,长径比的影响可以忽略。R-134a的CHF参数趋势与典型水的CHF参数趋势相似。Katto的模化方法在低临界含气率甚至是负临界含气率下都有很高的精度。将R-134a的CHF实验数据通过模化方法转换成等效水数据,并与CHF查询表(LUT)-2006进行了比较。评价结果表明,即使在几乎没有过冷CHF数据的压水堆工况,LUT-2006仍具有很高的预测精度。 相似文献
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在高温高压实验回路上进行了水在竖直管内向上流动的临界热流密度(CHF)实验研究。共获得117组数据,实验参数为:压力p=6.37~14.7MPa;质量流速w=571~5466kg/m2·s,进口欠热度△hi=96~744kJ/kg;出口含汽xc=-0.094~0.702.用数学回归整理成经验关系式。该式与实验数据的总均方根偏差为5.33%.同时,将Ahmad和张振杰氟里昂与水模化转换因子在应用范围内作了一些数学处理,实现了计算机快速双向模化转换,并用氟里昂和水的CHF数据对上述两种模化方法进行了验证.结果表明,这两种模化方法都能较好地模拟单通道内水和氟里昂竖直向上流动沸腾的CHF现象.其总均方根偏差在10%以内。在本实验参数范围内,张振杰模化结果在数据分布和均方根偏差上稍优于Ahmad法. 相似文献
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B. N. Kolbasov 《Journal of Fusion Energy》1997,16(3):285-290
The paper seeks to provide a summary report of observations and results of some Russian fusion safety studies performed in 1996. Release of tritium and helium from neutron irradiated beryllium at relatively high neutron fluences has a burst nature. With the growth of the beryllium temperature-increase rate to 90 K/s, the temperature of tritium burst release decreases from 800 to 450–500°C and for helium decreases from 1200 to 500°C. Characterization of carbon and tungsten dust produced in experiments simulating plasma disruptions revealed that dust particle distribution of sizes for graphites and carbon fiber composites has a bimodal nature with maxima in the range of 0.01–0.03 and 2–4 m for composite UAM and in the range of 0.14–0.18 and 2–4 m for graphite MPG-8. Chemical reactivity of beryllium with air was studied as well. A mathematical model for beryllium weight gain under its chemical interaction with air at temperatures of 700–800°C as a function of beryllium porosity, temperature, and interaction duration was developed. 相似文献
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Several changes to the focus of Computational Intelligence in Nuclear Engineering have occurred in the past few years. With earlier activities focusing on the development of condition monitoring and diagnostic techniques for current nuclear power plants, recent activities have focused on the implementation of those methods and the development of methods for next generation plants and space reactors. These advanced techniques are expected to become increasingly important as current generation nuclear power plants have their licenses extended to 60 years and next generation reactors are being designed to operate for extended fuel cycles (up to 25 years), with less operator oversight, and especially for nuclear plants operating in severe environments such as space or ice-bound locations. 相似文献
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On the basis of the previously described increase in internal friction in uranium during heating, a semiquantitative evaluation was made of the dependence of increase in internal friction on the rate of heating, frequency and amplitude of vibrations. The results of the calculations agree satisfactorily with data obtained experimentally. A study was made of the effect of the initial state of the specimen on the increase in internal friction at the initial stages of heating. 相似文献
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Momo Takada Toshihiro Yamada Teruhiko Takahara Satoru Endo Kenichi Tanaka Tsuyoshi Kajimoto 《Journal of Nuclear Science and Technology》2017,54(4):452-458
Downward migration of 137Cs in soils was studied in three mixed deciduous forests c.a. 40 km northwest of the Fukushima Daiichi Nuclear power plant (FDNPP), Japan. We selected three different types of forest regarding to environmental condition such as slope inclinations and snow coverage conditions at the time of deposition. We examined temporal changes in the vertical distribution of 137Cs from litter layers to 10 cm soil depth for two years (2.3 to 4.3 years after the FDNPP accident in 2011). At all three study sites, the 137Cs in the litter layer had largely migrated to surface soil by 2013. After 2014, about 80% of the 137Cs in forest soils (litter layer to 10 cm soil depth) remained within 0–5 cm soil layer. The vertical distribution had not changed substantially since 2014, suggesting that changes to the downward migration rates of 137Cs in soils drastically decreased with time. In addition, small amounts of migrating 137Cs could not be detected by the present method because there was a large spatial variation in the distribution of soil 137Cs. The results showed similar patterns of soil 137Cs distribution among the three study sites although there were differences in the environmental conditions. 相似文献
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自噬对鼻咽癌(Nasopharyngeal carcinoma,NPC)具有抑瘤和促瘤双重作用。自噬在NPC发生、发展及转归中起重要作用:低水平、基础自噬有利于细胞的自我保护与新陈代谢,是NPC放、化疗抵抗的重要因素之一;高水平、过度自噬则可导致自噬性细胞死亡,是基于自噬靶点的NPC治疗基础。自噬剂的研发与应用是实现自噬水平调控的关键环节,自噬抑制剂或自噬诱导剂可增敏NPC放、化疗甚至诱导其自噬性细胞死亡,但其作用机理颇为复杂且迄今尚未完全明了。本文着重综述自噬与NPC放疗研究进展,并探讨自噬作为新靶点的NPC治疗前景,尤其X射线作为自噬剂以诱导NPC发生治疗性的自噬性细胞死亡。 相似文献
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Ke Deng Ling Wang Zheng-Hai Xia Yu-Hua Ma Lai-Lai Qin Qin Zhang Jia-Yu Liu Jian Yao Wei Liu 《核技术(英文版)》2018,(5)
Tritium concentrations in precipitation can be used as a criterion to evaluate the tritium baseline of the environment. The tritium concentration in precipitation in Shanghai during 2014-2015 was determined. Values ranged from 0.68 ± 0.04 to 4.11 ± 0.39 Bq/L, and it showed a decreasing trend compared with historical data; however,the values were slightly higher than the natural background tritium level. Additionally, the tritium concentration shows a seasonal variation: It was higher in autumn and winter and lower in summer and spring. A comparison of concentrations in precipitation in Shanghai and around the Qinshan Nuclear Power Plant reveals no correlation,implying that the nuclear power plant operations may not affect the environment of Shanghai. Thus, the raised tritium concentrations in Shanghai might be due to the effects of monsoons, spring leak, raindrop, or other activities that generate tritium there. Those activities may include chemistry research that uses tritium as a tracer. 相似文献