利用数值模式和示踪试验确定某厂址地区大气扩散参数北大核心CSCD

利用WRF数值模式和CALPUFF扩散模式相结合的技术手段分析研究某沿海厂址大气扩散参数,并通过现场示踪试验验证了数值模式模拟结果的可靠性和模拟方法的适用性。结果表明,CALPUFF扩散模式无论从扩散因子数量值还是分布范围上,与现场示踪试验结果均能保持较好的一致性,CALPUFF扩散模拟结果能较好地反映当地大气扩散实际特征。通过与P-G和IAEA扩散参数比对得出,CALPUFF数值模式结果确定的厂址大气扩散参数符合大气扩散特征的一般规律;在考虑厂址实际下垫面和流场特征情况下,CALPUFF数值模式确定的扩散参数整体较P-G扩散参数偏大,其扩散参数值能较真实地反映该地区气载污染物的扩散能力。     

不同大气稳定度分类法及扩散参数方案对CALPUFF模拟结果的影响及拟合湍流方案的研究

通过沿海某核电厂址在不同大气稳定度条件下开展的示踪试验,验证了CALPUFF模式中三种大气扩散参数方案在不同大气稳定度条件下的数值模拟效果。研究结果表明,实测湍流方案的模拟效果受大气稳定度分类结果的影响较小,综合评估结果最好。在模式模拟大气稳定度分类结果和基于气象塔实测数据的大气稳定度分类结果一致的条件下,微气象方案模拟结果略差于实测湍流方案模拟,好于PG方案。在环评重点关注的不利天气条件下,采用微气象方案或PG方案的模拟结果可能会与实际浓度分布结果有偏差。为了解决长期实测湍流数据不易获取的问题,将用于大气稳定度分类的气象塔实测数据及对应时段的湍流观测资料进行拟合,构造出各大气稳定度条件下湍流脉动标准差方程。统计结果表明,结合了大气稳定度指标的拟合湍流方案模拟效果良好,对于提高核电厂大气扩散模拟效果具有一定的实用意义。     

复杂地形上的风场内插方法

针对复杂地形风场的诊断,本文提出了一种适合于起伏地形的权重内插方法,通过引入一个表示地形伏变化程度的因子,构造了一种新的权重函数,通过与只考虑距离因素的反平方内插方法的比较发现,在起伏地形条件下,采用这种新权重函数,可以有效地排除那些可能对计算结果产生干扰的观测点,用新权重函数计算得到的风场无论是风速还是风向都比反平方内插风场更接近实测风场,因此它更适合在起伏地形条件下使用。     

内陆代表性厂址事故扩散因子不同估算方法的比较

针对内陆核电选址中小风、静风频率较高的厂址,分别采用美国核管会(NRC)导则推荐方法和运用三维客观诊断风场与Lagrangian烟团模型模拟整年8 760小时逐时排放方法,计算了湖南桃花江厂址事故工况下的大气扩散因子,探讨复杂条件下大气扩散模型的适宜性。研究表明:在非居住区边界概率论方法计算的最大小时事故扩散因子较烟团模型计算方法保守;Lagrangian烟团模型计算的小时事故扩散因子在某些方位大于概率论方法结果,某些远距离子区的扩散因子大于近距离子区;对于释放时间相对较长的情形,导则方法估算结果仍偏小。由此可见,导则推荐方法得到的扩散因子存在不保守的情形,建议在计算复杂地形、小静风频率较高的内陆厂址事故扩散因子时慎重选择扩散模型。     

Ca^(2+)盐溶液在高庙子膨润土中的扩散研究北大核心CSCD

高放废物地质处置库近场地下水可能会对处置库内的屏障体系产生影响,降低处置库的安全稳定。为研究地下水中盐离子在处置库内缓冲回填体系的扩散规律,本文开展了静态无外荷载条件下内蒙古高庙子(GMZ)膨润土在Ca^(2+)盐溶液中自发渗吸的吸附扩散室内试验。从土的微观结构和经典扩散理论对Ca^(2+)在不同干密度和初始饱和度的膨润土试样中的自发扩散规律进行了分析。研究结果表明,在膨润土初始饱和度相同的情况下,试样阻滞系数随其干密度增加而增大,此时Ca^(2+)的扩散能力减弱;当膨润土干密度相同时,随着初始饱和度的增加基质吸力作用减弱,阻滞系数减小,Ca^(2+)的扩散能力减弱。     

高架排放及大粗糙地形条件下稳定度分类方法对大气扩散计算结果的影响

本文介绍在高架排放及大粗糙地形条件下稳定度分类方法对大气扩散计算结果的影响。采用五种不同的稳定度分类方法,对在西德卡尔斯鲁厄核研究中心(KfK)进行的一系列(22次)高架源(H=100m)大粗糙地形(地面粗糙长度 Z_0≈1.5m)条件下的大气扩散示踪试验数据作了统计分析。结果表明:在大粗糙地形及高架排放条件下,用高斯烟羽模式预报的归一化扩散因子与其实测值符合较好;对同一系列示踪试验数据,用不同稳定度分类方法分析处理会得出不同的弥散系数;在采用推荐的扩散参数进行环境评价时,最好使用与推荐者采用的相同的稳定度分类方法     

不同扩散参数与气象条件对核电厂年均大气扩散因子的影响

基于田湾核电厂厂址1997～1999年和福建惠安核电厂厂址1995～1997年百米逐时气象数据，对四组不同扩散参数(厂址实测、IAEA推荐值、Briggs以及Pasquill参数系)对两核电厂厂址的年均大气扩散因子计算值的影响作了估算，分析表明，采用IAEA和Briggs扩散参数与厂址实测值的偏差小于20％。同时估算了不同年份气象数据对年均大气扩散因子的影响。     

温度对^(75)Se(Ⅳ)在我国北山花岗岩中扩散影响的再思考北大核心CSCD

本文对Se在我国高放废物地质处置库预选围岩北山花岗岩中的扩散研究进行了总结,包括研究方法、获取的有关数据以及尚待开展的工作等,重点分析了温度对^(75)Se(Ⅳ)在北山花岗岩中扩散的影响及可能的影响机制,旨在为国内同行提供有益参考。     

海岛下垫面对核事故核素扩散影响规律研究

为研究核事故发生后气载核素在海洋环境中的扩散,以海岛核电厂为研究对象,采用计算流体动力学（CFD）模拟的方法对海岛核电厂各下垫面要素、风速变化、喷口速度变化进行了模拟,并用风洞实验验证CFD模拟的准确性。结果表明,山体会对地面最大扩散因子产生显著影响;平台的高度增加时,地面最大扩散因子降低,出现距离更靠近喷口;风速的增大会使得面最大扩散因子出现位置后移;喷口速度增大会使得地面最大扩散因子变小,其出现位置后移;在喷口速度变化的情况下,地面最大扩散因子的CFD模拟值和高斯烟羽模型计算值呈倍数关系,并以此对高斯烟羽模型进行了修正。      

Development of local-scale high-resolution atmospheric dispersion model using large-eddy simulation. Part 4: turbulent flows and plume dispersion in an actual urban area

We have developed a local-scale high-resolution atmospheric dispersion model using large-eddy simulation (LOHDIM-LES) to assess the safety at nuclear facilities and to respond to emergency situations resulting from accidental or deliberate releases of radioactive materials (e.g., a terrorist attack in an urban area). In Part 1, the unsteady behavior of a plume dispersing over a flat terrain was successfully simulated. In Parts 2 and 3, LESs of turbulent flows and plume dispersion around an isolated building and in building arrays with different obstacle densities were performed, which showed the basic performance comparable to wind tunnel experimental technique. In this study, we apply the LES model to turbulent flows and plume dispersion in an actual urban area. Although some of the turbulence and dispersion characteristics are quantitatively different from the wind tunnel experimental data, the distribution patterns are generally similar to those of the experiments. It is concluded that our LES model simulates reasonably the unsteady behavior of turbulent flows and plume dispersion even for complex heterogeneous urban areas.     

核事故下放射性核素多介质耦合弥散模型

建立了高斯烟团模型与欧拉输运扩散模型的耦合模型,以实现放射性核素在大气以及水体中弥散的耦合。通过对大气和水体弥散模型进行对比,验证了各个模块的正确性。基于该模型,对中国铅基研究实验堆发生燃料组件熔化事故释放的~(131)I进行仿真分析,对该核素在大气以及水体中的浓度分布进行评估。模拟结果表明:事故发生2 h后大气污染主要分布在10 km内,水域污染主要分布在10~20 km处;在该模拟条件下,铅基堆发生燃料组件熔化事故后对大气和水体造成的影响均低于国家限值。     

Development of local-scale high-resolution atmospheric dispersion model using large-eddy simulation. Part 3: turbulent flow and plume dispersion in building arrays

We have developed a LOcal-scale High-resolution atmospheric DIspersion Model using Large-Eddy Simulation (LOHDIM-LES) to assess the safety at nuclear facilities and to respond to emergencies against accidental or intentional release of radioactive materials (e.g., a terrorist attack in an urban area). In Part 1, the unsteady behavior of a plume over a flat terrain was successfully simulated. In Part 2, a new scheme to generate a spatially developing turbulent boundary layer flow was proposed. Then, the large-eddy simulation (LES) model for turbulent flow and plume dispersion around an isolated building was validated. In this study, we extend the LES model to turbulent flows and plume dispersion in various building arrays that represent typical urban surface geometries. Concerning the characteristics of flow and dispersion in building arrays, the flow patterns associated with obstacle densities and the distribution patterns of mean and root-mean-square (r.m.s.) concentrations agree well with those of the wind tunnel experiments. It is shown that the LES model successfully simulates the unsteady behaviors of turbulent flows and plume dispersion in urban-type surface geometries.     

Development of Local-Scale High-Resolution Atmospheric Dispersion Model Using Large-Eddy Simulation Part 1: Turbulent Flow and Plume Dispersion over a Flat Terrain

We have developed a local-scale atmospheric dispersion model using large-eddy simulation (LES) to accurately predict the dispersion behavior of radioactive materials for the safety assessment of nuclear facilities and emergency responses against accidental release from nuclear facilities and intentional release by terrorist attack within a populated urban area. In this study, we validate LES basic performance on plume dispersion over a flat terrain within the atmospheric turbulent boundary layer, as a first step. When compared to previous experimental data, we have found that the LES model has successfully generated a spatially-developing turbulent boundary layer flow that has characteristics corresponding to those of atmospheric wind. Furthermore, the dispersion characteristics obtained by LES, such as mean concentrations, variances of concentration fluctuation, peak concentrations, and concentration fluxes, are similar to previous experimental results. Although the current numerical simulation model requires considerable CPU time statistics of concentrations, the LES model can be used as an effective tool for accurately assessing the spatial extent of contaminated areas in detail. We anticipate reducing the computational burden by using an advanced computational method, and, as a practical matter, using the LES model for emergency responses.     

双束强辐照对氧化物弥散强化铁素体型合金强化相稳定性影响

采用双束复合辐照装置,研究了He存在条件下,强辐照对长期时效后的ODS合金中强化相(Y2O3)的稳定性和辐照损伤特征的影响。实验结果表明:双束强辐照下,ODS合金中强化相不稳定,发生聚集长大并造成附近基体中Ti、Y浓度增高,导致空洞尺寸和空洞肿胀增加,并对这一结果从理论上进行解释。     

Development of regional downscaling capability in STEAMER ocean prediction system based on multi-nested ROMS model

Oceanic regional downscaling capability was implemented into Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) developed by Japan Atomic Energy Agency to enable us to predict more realistically the oceanic dispersion of radionuclides at higher spatiotemporal resolutions for broader applications. The system consisted of a double-nested oceanic downscaling circulation model with tidal forcing and an oceanic radionuclide dispersion model. This system was used to comparatively examine downscaling and tidal effects on the dispersion of radionuclides hypothetically released from the Fukushima Daiichi Nuclear Power Plant in the colder season. The simulated dissolved ¹³⁷Cs distribution was different from that obtained using coarser-resolution models because downscaling enhanced both horizontal and vertical mixing. The suppression of horizontal mixing and the promotion of vertical mixing by tidal forcing synergistically reduced offshore ¹³⁷Cs transport. In addition, the submesoscale effects strengthened the three-dimensional ¹³⁷Cs fluctuations by <10 times, while the tidal effects promoted slightly increased the intensity of three-dimensional ¹³⁷Cs fluctuations by approximately 3%. This indicated that the submesoscale effects substantially surpassed tidal forcing in oceanic mixing in the coastal margin off Fukushima in the colder season.     

Investigation of the High Pressure Regimes Effects on the Neutron Production in Plasma Focus

Effects of high pressure regimes on the thermal mechanism of neutron yield and anisotropy factor with respect to the capacitor bank energy are presented by using moving boiler model. It is found that at high pressures, the thermal fusion reactions have a considerable effect on the neutron yield and anisotropy factor. We have compared the manner of the anisotropy in two low and high pressure discharges to investigate different behavior of the anisotropy factor as a function of bank energy in the difference working regimes of pressure for Dena PF.     

Effects of solute elements on hardening and microstructural evolution in neutron-irradiated and thermally-aged reactor pressure vessel model alloys

Nanometer-sized Cu-enriched solute clusters containing Mn, Ni, and Si atoms are considered as the primary embrittling feature in reactor pressure vessel steels. In order to understand the effects of solute atoms Mn, Ni, and Si on hardening and cluster formation, reactor pressure vessel model alloys FeCu, FeCuSi, FeCuNi, and FeCuNiMn were irradiated at 290 °C in a research reactor. Thermal ageing at 450 °C was also carried out to compare with the results in the neutron irradiation. The addition of Mn resulted in larger hardening and higher cluster number density in both thermal ageing and neutron irradiation. In FeCu0.8NiMn alloy, the size distribution of Cu-enriched clusters formed in 62-h thermal ageing (almost peak hardening) was very similar to that formed in the neutron irradiation, indicating they are on a similar growing stage. But the average Ni and Mn composition in clusters formed in neutron irradiation was higher. A good linear relationship between hardening and the square root of cluster volume fraction for both neutron irradiation and thermal ageing data was found.