核设施正常工况下放射性气态流出物对公众影响评价的现状与建议

本文介绍了在核设施正常工况下放射性气态流出物环境影响评价中,气象参数获取方法、大气稳定度联合频率的变化、大气弥散模式调整、剂量转换因子的选用等因素对长期大气弥散因子或最大个人剂量的影响,提出了规范和简化评价方法的建议。     

核电厂放射性气态流出物大气弥散模型现状与展望

介绍了核电厂气态流出物在大气输送和扩散过程中放射性核素环境影响评价中常用的几类大气弥散模型,讨论了大气弥散模型的影响因素、模型不确定性分析和数据同化,以及大气弥散模型的应用前景和存在的问题.     

核设施气态流出物的环境γ吸收剂量计算及实验验证

采用有限烟云大气扩散模式，计算了中国原子能科学研究院的２座核反应堆烟囱排放的放射性气态流出物在核反应堆附近产生的附加吸收剂量。对１９９０－１９９２年间３年的实验测量结果逐年进行了比较，其偏差均在６２％以内。     

典型内陆厂址近场年均大气弥散和沉积因子不同计算方法的比较

采用高斯直线烟流模式XOQDOQ和三维拉格朗日高斯烟团模式CALPUFF,分别计算了我国某一地形复杂、小静风频率较高的典型内陆厂址近场5 km半径范围的年均大气弥散因子和干沉积因子,并对结果进行了对比分析。研究表明:两种模式得到的近场年均大气弥散因子和干沉积因子分布、以及最大值出现位置有一定的差异。就扇区平均值而言,2 km半径以内XOQDOQ计算的方位最大弥散因子和干沉积因子分别是CALPUFF计算值的5倍和3倍左右;2 km以外两种模式计算结果差别减小,CALPUFF计算的方位最大干沉积因子大于XOQDOQ计算值。因而,对于地形复杂和小静风频发的厂址,在评价核电厂正常运行工况下气载流出物的辐射影响时,应结合厂址具体的环境和人口分布特征,在需要精细评价的情况下,宜选用其它适宜的大气扩散模式。     

聚变堆失真空事故下氚的大气扩散模拟研究

聚变反应堆发生失真空事故的情况下氚会泄漏到环境中，氚大气扩散模拟是聚变堆事故后果评价的重要内容。基于高斯烟团模型以及Pasquill稳定度分类方法，考虑重力沉降、烟气抬升、风速等因素的影响，建立了适用于事故下瞬态分析的大气扩散模型，在高斯烟团模型中加入修正了像源贡献的地面反射系数，提高了模型对于地面边界处干沉降的计算效果。选取加拿大氚气释放实验和美国萨凡那河工厂氚释放事故验证了所建立模型的准确性，模型的计算结果与HotSpot 3.0和UFOTRI软件的精度相当。选取国际热核聚变实验堆（International Thermonuclear Experimental Reactor,ITER）的失真空事故作为研究对象，分析了氚的分阶段释放、风速以及释放高度对氚扩散分布的影响。结果表明：氚的分阶段释放会导致沿下风向出现两个高放射性区域；释放高度和风速的增加会强化氚在大气中的扩散行为，从而减弱放射性在近场的积聚。     

防城港核电厂气态流出物取样监测探测限影响因素分析

对防城港核电厂一期机组中气态流出物取样监测的最小可探测限的影响因素进行分析,计算了取一定置信度和相对标准偏差时对应的气态流出物中不同核素的最小可探测限。分析了不同测量时间下,相对标准偏差与净计数率的关系。结果表明当机组烟囱气态流出物中的放射性排放速率至少达到计算水平时,测量值才能高于系统最小可探测限。该结果对其它核电机组制订气态流出物监测大纲具有一定参考作用。     

田湾核电站气态流出物对环境γ剂量率的影响

对田湾核电站2号机组压力容器开盖期间气态流出物释放导致电站周边环境γ剂量率的变化从实测值和理论计算值进行比较分析。分析结果表明,实测值和理论计算值基本上是吻合的;同时验证了核电站正常运行期间排放的气态流出物对于环境γ剂量率的影响基本在天然本底波动范围之内。即使在低风速的情况下,气态流出物对于环境γ剂量率的影响也主要在下风向,随距离的增加迅速减小;对于上风向和侧风向的影响则小的多。     

核电厂气载流出物大气弥散因子不同计算方法比较研究

当前,基于核电厂气载放射性流出物环境影响的评价模式种类较多,然而这些模式及其开发的程序多用于评价过程,专门针对环境后果影响审评的应用较少。本文从分析核电厂气载放射性流出物大气弥散的相关导则标准以及基于此开发的相应程序入手,针对典型核素,采用C-Airdos,ROULEA-2.0和Fluidyn-PANACHE等程序,以我国自主设计的CAP1400压水堆重大专项示范工程石岛湾核电厂所在地环境数据为基准,开展正常运行工况下大气弥散因子模拟计算,与石岛湾核电厂环境影响评价报告所采用的Y3001程序计算结果进行比较分析,推荐适用于核电厂正常运行工况下气载流出物环境影响的审评模式及程序,为我国核电厂环境影响审评提供有益的技术参考。     

秦山核电站正常运行辐射环境影响评价系统研发

正为保证对秦山核电站9台机组在正常运行情况下放射性流出物对核电站周边80km×80km范围内环境和公众辐射的影响评价,基于秦山基地机组多厂多堆的分布特征,开发了一套适用于秦山核电站的辐射环境影响评价系统,该系统通过计算核电站在正常运行情况下气态和液态流出物浓度从而分析出放射性核素对人体造成的剂量影响。系统的理论模块分为气态流出物排放模块和液态流出物排放模块两部分。在气态流出物排放模块中,加入了不同下垫面类型对应的不同扩散参数的计算方法,并考虑了干湿沉降及多排放源     

600MWe核电站正常运行工况下气态排出物环境弥散模式、参数与程序

600MWe核电站正常运行工况下气态排出物弥散模式在中国核工业三十年辐射环境质量评价的基础上尝试给出了混合释放年均大气扩散因子的数学表达式。计算中考虑了静风影响及下述诸因子影响的修正:混合层,干、湿沉积,放射性衰减,建筑物影响等。并能给出下述各照射途径的剂量:烟羽浸没外照射,烟羽吸入内照射,地表沉积外照射,食     

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.     

RODOS系统中两种大气弥散模型链的比较

通过对RODOS系统中两种大气弥散模型链在均匀和非均匀气象条件情况下风场与大气扩散的计算结果进行比较，表明：在进行核事故后果评价中采用风场模式确定烟羽输送轨迹是非常重要的，特别是对于复杂地形厂址；分段烟羽模式的ATSTEP模型在整个评价区采用单点风资料，仅在乎坦均匀地形和稳定条件下是一种有用的近似，对于复杂地形厂址其适用性将受到限制；从对风场的处理方法和对大气扩散的模拟角度看，采用Lagrange移轨迹烟团模式的RIMPUFF模型模拟的结果相对要好。     

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 5: detailed simulation of turbulent flows and plume dispersion in an actual urban area under real meteorological conditions

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 parts 1–4, LESs of turbulent flows and plume dispersion over a flat terrain, around an isolated building, within building arrays with different obstacle densities, and within an actual urban area were performed, which showed the basic performance comparable to wind tunnel experimental technique. In this study, we extend the LOHDIM-LES to turbulent flows and plume dispersion in an actual urban area under real meteorological conditions by coupling with a meso-scale meteorological simulation model. The LES results of wind speed, wind direction, and concentration values are generally reproduced well. It is concluded that our coupling approach between LES and meso-scale meteorological models is effective in detailed simulations of turbulent flows and plume dispersion in urban areas under real meteorological conditions.     

小型动力堆核事故后放射性核素海洋大气扩散研究

应用于海洋的小型核反应堆技术日渐成熟,但目前核事故大气扩散研究主要针对于沿海或内陆情况。为使大气扩散计算模型适用于海洋环境,本文对高斯烟羽模型进行了修正,应用MACCS程序研究了小型动力堆严重事故所造成的后果。结果表明,若烟羽未抬升,可溶性核素积分浓度垂直分布受水体影响较大,低空的核素积分浓度明显降低;若烟羽被抬升,源项附近海面的核素积分浓度较低,水体对其产生的影响较小;整个扩散过程中,水体主要影响海面附近核素积分浓度大的区域。     

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.     

核事故早期应急响应的预报模式及其设计方案

风场预报和烟羽浓度预测是核事故早期应急响应放射性后果评价系统的主要内容。基于将风场预报和烟羽浓度预测作为一个系统的考虑,介绍用于核事故早期应急响应的预报模式和设计方案。风场预报,以质量守恒的风场诊断模式提供的三维风场为初始场,采用非静力平衡、完全可压缩的大气动力学模式。烟羽浓度预测,采用粒子随机游走大气扩散模式,该模式所依赖的平均风速和湍流脉动参数均来自非静力平衡、完全可压缩的大气动力学模式。     

随机游走大气扩散模型在核事故应急中的开发和应用

烟羽浓度预测是核事故早期应急响应放射性后果评价系统的主要内容之一.描述了大气扩散本身随机的特点,介绍了自行开发随机游走大气扩散模型Random Walk,并与现有欧共体开发的核应急决策支持系统RODOS中的拉格朗日烟团模型RIMPUFF进行比较验证.结果表明,两者计算结果相当吻合,但Random Walk计算出的烟羽范围比RIMPUFF计算出的稍小.随机游走大气扩散模型Ran-dom Walk能够较好的模拟核事故发生条件下的大气扩散过程,可以作为核事故应急决策系统的一个大气扩散模块,为早期应急和后果评价提供更接近实际的信息.     

分段烟羽模型和烟团模型在核事故应急中的应用比较

为了研究分段烟羽模型和烟团模型在核事故应急中的适用性 ,对不同流场条件下分段高斯烟羽模型和烟团模型的模拟结果进行了比较。在均匀稳定流场中 ,两种模型的模拟结果相近 ;而在非均匀稳定的流场中 ,分段烟羽模型的模拟结果呈现明显的不连续性。而且对于瞬时释放 ,烟团模型比分段烟羽模型更接近实际情况。通过对模型性能的对比 ,并考虑应急决策支持的要求和我国核电站的厂址条件 ,推荐采用烟团模型     

用于计算较大尺度面源气载放射性释放的环境辐射剂量的一种套网格模型

本文介绍一种用于较大尺度面源气载放射性释放环境影响评价的套网格模型，该模型采用扇形网格和正方形网格相结合，以扇形网格为基本框架，而将面源区和近源区划分为正方形网格，在进行大气扩散估算时，为合理模拟空气浓度分布，在面源区和近源区，采用大气湍流扩散实验室模式；在其它区域，将面源视作若干个虚拟点源，采用高斯烟羽模式。在进行环境辐射剂量估算时，先将正方形网格点的空气浓度值内插到扇形网格，然后按扇形网格下的