远东地区核风险厂址释放的气载放射性污染物长距离迁移的模拟

气载放射性物质在大气中的长距离迁移问题逐渐受到关注。我们开发建立了轨迹模式TraModel和粒子扩散模式ParModel,用以模拟计算气载物质的迁移轨迹和扩散影响,并利用欧洲示踪实验(ETEX)数据对模式进行验证,同时也与国外同类模式进行了比对。结果表明,本研究所开发的模式具有较高的精度。利用美国国家环境预测中心(NCEP)的气象数据进行模拟计算,将其用于模拟我国田湾、秦山核电站以及俄罗斯远东Vladivostok(海参崴)核风险厂址释放的放射性物质的跨国界迁移。模拟结果表明,相对于等熵轨迹,三维轨迹能更真实地反映污染物的实际迁移,对于长距离迁移问题的概率分析,等熵轨迹和三维轨迹的模拟结果基本相同。释放高度对大气迁移途径有显著影响,故由一个释放高度得到的模拟结果用于其它释放高度时应当慎重。此外,由于在中国东部沿海地区气象场的复杂性,特别是受东亚季风的影响,释放点不同地理位置的影响结果也是很不相同的。这些模式、方法今后可用于开展远东核风险厂址大气迁移的概率风险分析以及事故后果评价。     

福岛核事故放射性物质释放对周边地区的概率影响分析

模拟了福岛核事故放射性物质释放对周边地区,尤其是对我国关心区域的影响,利用2004年至2008年3-5月五年间的气象数据,以日本福岛第一核电站为中心,考虑经纬度各±0.2°的区域设置4个释放点,计算福岛核电站每天8次的正向3D轨迹,轨迹的起始高度为50 m,轨迹时间间隔为3h,轨迹长度为5d.4个释放点五年共14 720条轨迹,利用轨迹计算结果通过聚类分析获得其大气迁移途径,统计分析了放射性物质到达关心区域的频率以及大气迁移和快速迁移的概率场.结果表明,在春季三个月到达我国各关心点的频率普遍相对偏低,其中5月份最高,如:哈尔滨为0.9％,上海为0.6％,台湾为0.2％,北京为0.1％,平均迁移时间分别为3.2d、4.2d、4.5d和4.6 d;3月的频率最低,3月到达台湾的频率为0.1％,到达哈尔滨的频率为0.1％,到达我国其余关心区域的频率均为0.日本福岛第一核电站春季的气流迁移和快速迁移的概率场结果与上述根据逐条轨迹途径对关心点的影响分析结果是一致的.同时,从概率场结果还可看出对其它地区的影响情况.     

BESⅢ主漂移室模拟真实化调试研究

以BESⅢ上开发的主漂移室模拟软件为基础,仔细研究并建立了一套规范、有效的主漂移室模拟真实化调试方法。该方法基于对主漂移室响应机制以及真实数据中探测器工作状态的深入理解,建立恰当的参数化模型,通过调试丝击中效率及丝空间分辨,实现主漂移室模拟真实化。论文介绍了BESⅢ主漂移室模拟真实化调试的原理、利用真实数据进行调试的过程以及调试的性能表现。采用这套调试方法,通过调试丝击中效率和空间分辨可以获得恰当的探测器模拟输入参数,使模拟数据与真实数据径迹重建效率的差异达到1%的水平。     

LSO晶体射线荧光图像转换屏性能研究

理论分析LSO晶体相对ST-401塑料闪烁体的发光效率,并在平均能量为1.25 MeV的γ射线源上进行标定,实验测得20 mm厚度LSO晶体的相对灵敏度是10 mm 厚度ST-401塑料闪烁体的约60倍,实验数据与理论数据相符,同时理论计算了LSO晶体的空间分辨,相对强度降低50%时的线扩散约为0.18 mm,优于ST...     

典型超临界二氧化碳强迫对流传热关联式评价分析

对不同类型的超临界二氧化碳(S-CO_2)强迫对流传热关联式进行分类整理,并基于公开发表的实验数据,对典型S-CO_2强迫对流传热关联进行评价。结果表明:传热关联式在拟临界区域预测结果与实验结果存在较大偏差,在传热退化恢复阶段预测能力较差;Dong Eok Kim和Moo Hwan Kim关联式预测结果与实验数据吻合相对较好,84.53%的预测值与实验值偏差在±30%以内。结合评价结果对典型传热关联式的结构特点进行了分析讨论。     

基于拉格朗日混合单粒子轨迹模式（HYSPLIT）的核污染物扩散数值预报技术

本研究利用拉格朗日混合单粒子轨迹模式（HYSPLIT）开展了核污染物数值预报试验。欧洲示踪试验和虚拟事故情景下的模拟预报试验结果表明,HYSPLIT模式模拟的1 h内轨迹最小绝对误差约为0.2°,该模式可以有效地预报核污染物的扩散轨迹。模拟轨迹误差主要受风向和风速的影响,且初始状态误差会使轨迹模拟的误差随着预报时效增加而逐渐增大;对于单次轨迹模拟,模式模拟轨迹会存在偏差,但在一定时间范围内,轨迹模拟可以很好反映示踪剂在释放后空间范围内整体的分布特征;利用大气扩散模式HYSPLIT和中尺度天气预报模式（WRF）,可以实现区域核污染物的数值预报,模式可以预报出事故区域核泄漏物质的扩散路径和浓度分布。     

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。     

集合扩散模拟技术在应急决策中的应用研究

应用集合扩散模拟的概念,结合不同的气象场与扩散场模式,以某厂址的现场实验为研究对象进行中小尺度集合大气扩散模拟研究。将多模式模拟结果与现场实验结果进行集合分析,从空间分析、时间分析与离散度检验三方面对各类集合分析指标进行研究。结果表明:集合扩散模拟与分析可综合考虑多模式计算结果,给出烟云可能覆盖区域范围与概率、不同置信度水平的烟云浓度分布、关心点(区域)的烟云浓度变化、烟云到达与离去时间概率等,同时可结合监测结果进一步判断与修订模拟结果从而更加接近真实值。将集合扩散模拟方法应用于应急决策领域具有现实指导意义。     

PIXE和XRF用于北京新镇地区PM2.5源解析研究

大气颗粒物(APM)对人体健康和环境的影响越来越受重视,我国增设了PM2.5标准,同时提出了大气污染的专项治理措施。本文采用GENT二级取样器在北京郊区新镇进行连续取样,并用质子激发X射线荧光分析和能量色散X射线荧光分析对北京新镇地区收集到的140个大气颗粒物样品进行了多元素分析,对测量数据进行了可靠性评价和数据重组,结合取样、气象等参数建立了新镇地区大气颗粒物污染成分数据库,利用正矩阵因子模型进行污染源解析研究。初步认定了5个主要污染源,即燃煤源(29.2%)、汽车尾气和垃圾焚烧源(26.2%)、建筑工业源(23.3%)、土壤源(15.4%)以及含氯工业源(5.9%)。并结合气象数据进行了污染源来源研究,根据条件概率函数和潜在源贡献函数的计算结果作出了污染源来源分布图,发现污染来源与周围环境基本符合。     

基于伴随粒子的快中子成像系统角分辨研究

不同于传统的快中子成像系统，采用伴随粒子成像技术无需机械准直即可消除大部分γ射线和散射中子的干扰，实现对厚重物体的高对比度成像。角分辨是影响系统成像质量的一项重要参数。通过理论分析，研究了入射离子的初始动量、靶点尺寸和探测器空间分辨等多个因素对系统角分辨的影响。利用基于GEANT4的模拟程序，计算了不同参数下被标记中子出射角分布的二维图像。分析及模拟结果表明，靶点直径和α探测器空间分辨率是影响角分辨的重要因素。为满足系统角分辨小于1°的设计目标，入射离子的初始动量变化范围应较小，靶点直径应小于1 mm，同时α探测器的空间分辨率应小于0.5 mm。     

基于三晶体耦合γ射线方向探测器的放射源定位

为了快速定位并寻回丢失的放射源,设计了一种由NaI、CsI、锗酸铋(Bi4Ge3O12,BGO)三种晶体与铅耦合组成的γ射线方向探测器,并采用基于蒙特卡罗方法的通用软件包MCNP(Monte Carlo N Particle Transport Code)研究了铅晶比例、射线能量、剂量率等因素对探测器角度分辨率的影响。结果表明,对于137Cs源,在空气吸收剂量率≥0.331μGy·h~(-1)处,定位角度偏差≤0.99°;对于60Co源,在空气吸收剂量率0.586μGy·h~(-1)处,测量的平均角度偏差为0.46°;对于水平距离7 m、高度4 m的3.7×107Bq 137Cs源,相对定位偏差约为5%。     

Predictability of a short-term emergency assessment system of the marine environmental radioactivity

ABSTRACT

A Short-Term Emergency Assessment system of the Marine Environmental Radioactivity (STEAMER) was developed at the Japan Atomic Energy Agency (JAEA) to forecast or reanalyze the oceanic dispersion of radionuclides that are released into the ocean around Japan from nuclear facilities during routine operation or in an emergency. STEAMER is currently in daily operation at JAEA to conduct single forecast simulation. The predictability of STEAMER is validated by utilizing oceanographic forecast and reanalysis data in this study. The oceanic dispersion simulations that use oceanographic reanalysis data as input data are assumed to have true solutions. Reanalysis data that has been optimized by data assimilation is the most reliable input for post-analysis. Rigorous oceanic dispersion simulations are conducted for the hypothetical release of Cs-137 from the Fukushima Daiichi Nuclear Power Plant. The predictability of the Cs-137 oceanic dispersion is quantitatively estimated over a forecast period. Moreover, ensemble forecast simulations are also performed applying the Lagged Average Forecast methodology and they successfully improve the predictability of the Cs-137 oceanic dispersion over that obtained using single forecast simulation. The ensemble forecast simulations need to be installed in STEAMER in the future.     

Calculation and measurement of migration coefficient of radon under laboratory conditions

Under laboratory conditions （i.e. a sealed system in which the temperature may vary according to air temperature）, the migration of radon in upward, downward and horizontal directions has been investigated. After a period of accumulation, the spatial distribution profile of radon was drawn on the basis of the experimental data. The profile showed whorl-shape with bigger ends. The longer the accumulation time, the bigger the whorl end, and the higher the radon concentration is. By fitting the experimental data by least-square statistical method, we find that the distributions of radon follow negative exponential functions in the upward, downward and horizontal directions. However, exponents for the three directions are not exactly identical. The upward migration is more effective than the downward one and both upward and downward migrations are more effective than the horizontal one.     

Validation of a Lagrangian atmospheric dispersion model against middle-range scale measurements of 85Kr concentration in Japan

The Lagrangian atmospheric dispersion model of the computer-based nuclear emergency response system WSPEEDI-II was validated with the measured ⁸⁵Kr concentrations in tens-of- to hundreds-of-km (middle-range) scale area by conducting dispersion simulations using the release rate from the nuclear fuel reprocessing plant in Rokkasho, Japan. The calculated weekly concentrations of ⁸⁵Kr in two simulation cases during April and September in 2008 agreed with the measurements within a factor of two at the sampling sites 170 to 2000 km away from the plant. However, the sensitivity analysis of horizontal grid resolution of the meteorological model ranging from 2 to 54 km showed that the calculated results had the dependency on the grid resolution, i.e., the calculated concentrations became low compared with the results with the grid resolution of 54 km as the grid resolution became high. An empirical modification of the horizontal diffusion parameter used for long-range dispersions by WSPEEDI-II was attempted based on the sensitivity analysis to reduce the redundant diffusion effect in dispersion simulations with relatively high grid resolution. The modified horizontal diffusion parameter contributed to reduce the dependency of calculated concentrations on the horizontal grid resolution.     

不同压强下氡气运移实验研究

氡气在空气中的运移研究是氡气测量和防护的基础理论问题。论文以实验为基础,采用活性炭累积测氡法,对氡气在不同气体压强下的运移规律进行研究。得出:氡气在空气中运移速度与空气压强有关,空气压强越大,运移速度越快,在低压状态下向下运移更加明显;对比氡气在竖直方向和水平方向上测量结果,不管压强高低,氡气运移在竖直方向上的运移能力远远超过水平方向;在不同压强情况下氡气平均速度估算,常压下向上运移平均速度为1.02×10-6m/s、向下运移平均速度为2.08×10-6m/s,低压下(相对真空度为-0.06 MPa)氡气的向上运移平均速度为0.91×10-6 m/s、向下运移平均速度为2.77×10-6m/s,与实际测量结果符合性良好。     

氡及其子体水平扩散系数测量研究

氡气运移的研究成果表明,氡气的运移具有方向性。本文从实验入手,采用静态、累积、高灵敏度的测氡方法,对氡累积水平扩散分布进行了测量。采用最小二乘法拟合方法对不同温度条件下氡及其子体的水平扩散系数进行了计算。实验研究结果表明,氡及其子体的水平扩散系数与温度的相关系数为0.92,两者呈线性正相关关系;在恒温(30℃)条件下的实测水平扩散系数为0.049cm2·s-1;要使氡在空气中的水平扩散系数达到经典值0.1cm2·s-1,其环境温度应达到40℃以上。     

Vapor heat transfer in post-CHF region including the effect of thermodynamic non-equilibrium

Vapor phase heat transfer in the post-CHF region is modelled using momentum-transfer analogy and allowing for thermodynamic non-equilibrium. The vapor heat transfer coefficient is determined by momentum-transfer analogy, using an appropriate two-phase friction factor. The degree of thermodynamic non-equilibrium, denoted by the ratio of actual quality to equilibrium quality, is correlated in terms of a dimensionless temperature difference which includes the superheated vapor temperature. This correlation is solved simultaneously with a heat balance equation to determine the actual quality and the vapor temperature. Post-CHF vapor heat flux, calculated by this method, is compared to experimental tube data from eight different sources at pressures up to 2830 psia and over a wide range of mass fluxes. Results indicate an average deviation of 14.9% between measured and predicted heat fluxes for 2854 data points.     

Heavy Ion Beam Probe Measurement in Turbulence Diagnostic Simulator

A numerical measurement module simulating a heavy ion beam probe was developed, and numerical measurements of electrostatic potential and density fluctuations are carried out for 3-D turbulent data generated by a global simulation of drift-interchange mode turbulence in helical plasmas. The deviation between measured and local values is estimated. It is found that the characteristic structures can be detected in spite of the screening e®ect due to the ¯nite spatial resolution.     

Field structure and electron life times in the MEFISTO electron cyclotron resonance ion source

The complex magnetic field of the permanent magnet electron cyclotron resonance (ECR) ion source MEFISTO located at the University of Berne has been numerically simulated. For the first time the magnetized volume qualified for electron cyclotron resonance at 2.45 GHz and 87.5 mT has been analyzed in highly detailed 3D simulations with unprecedented resolution. New results were obtained from the numerical simulation of 25,211 electron trajectories. The evident characteristic ion sputtering trident of hexapole confined ECR ion sources has been identified with the field and electron trajectory distribution. Furthermore, unexpected long electron trajectory lifetimes were found.