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     

描述气载放射性核素干沉积损失的积分耗减模式

描述烟柱中核素浓度因干沉积而减少的模式,目前有源耗减模式与表面耗减模式两种。前者数学运算简单,但人为地扩大了垂直混合能力。后者物理概念严谨,但计算量比前者大得多。本文提出的积分耗减模式,物理概念虽不及表面耗减模式严谨,但基本上克服了源耗减模式的主要弱点,数学运算也较简单。     

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。     

颗粒-壁面相互作用对石墨粉尘在高温气冷堆蒸汽发生器换热管表面沉积过程的影响

石墨粉尘在高温气冷堆蒸汽发生器换热管表面的沉积直接影响一回路放射性分布，因而备受学界和业界的关注。本文采用临界粘附速度模型研究石墨粉尘颗粒的碰壁过程，并将其耦合入蒸汽发生器一次侧的气固两相流模拟计算中，得到了石墨粉尘颗粒在换热管束间的输运和沉积规律。结果表明，考虑颗粒-壁面相互作用后，石墨颗粒沉积率显著减小，其与粒径的关系也有所不同。沉积率随粒径的增大先增大后减小，最大沉积率对应粒径约3 μm。空间分布规律上，小颗粒迎风第1排管沉积率相对最大，2 μm以上颗粒最大沉积率发生在第4～6排管。     

基于风洞实验的丘陵下垫面气溶胶大气扩散特性研究

核电厂正常运行或发生核事故时,会向大气释放一定量的放射性气溶胶,研究气溶胶在复杂下垫面的大气扩散特性对实现气载流出物辐射影响的准确评价具有重要意义。高斯烟羽或烟团模型被广泛用于大气扩散评价中,模型中的扩散参数描述了气溶胶受湍流作用扩散的强弱,需要针对不同的地形如平坦、丘陵下垫面进行校正。本文针对典型下垫面开展了气溶胶大气扩散风洞实验,采用激光粒子图像扩散参数估计方法,针对释放源高度不同的多组工况,统计分析了竖直截面内高分辨率的气溶胶浓度,根据高斯分布估计了下风向烟羽的上下边界及垂直方向扩散参数。结果表明：烟羽经过山体会出现整体抬升现象,这将导致山体后近地表浓度有所下降;烟羽经过山体前后出现浓度中心线两侧浓度分布不均现象,远离山体烟羽轨迹回归类高斯分布;释放源高度小于山体1/2高度的烟羽经过山体后轨迹趋于一致。高斯模型在丘陵下垫面适用度有限。     

核设施环境连续监测

叙述了用高气压电离室环境连续监测仪连续测量核设施气态流出物γ辐射剂量率的技术和方法。总结了一台连续监测仪在两座实验性核反应堆(15兆瓦重水堆和3.5兆瓦轻水游泳池式反应堆)附近环境中,连续测量三年(1990～1992)所获得的33450个数据资料。给出由于反应堆排放的惰性气体烟羽产生的外照射剂量。最高年份(1992年)值为53.8μSv,仅为天然本底值的9％。监测结果与用有限烟羽大气扩散模式计算结果进行了比较,在62％范围内一致。     

气溶胶粒径分布对肺模型评价氡子体有效剂量的影响

剂量学近似方法常用于评估氡子体有效剂量。在回顾ICRP66号肺模型的基础上,计算分析了气溶胶粒径对肺部区域沉积份额的影响。在此基础上,计算讨论了气溶胶粒径分布对氡子体有效剂量转换系数的影响,结合粒径分布实验测量值,综述了典型环境下氡子体有效剂量转换系数同未结合态份额及结合态粒径分布的关系。     

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,食入内照射。程序名为“ROULEA”。ROULEA程序包含四个模块,即INPUT模块、ANRTRI模块、CHIQV模块和DOSE模块,分别计算四维联合频率,年均大气扩散因子和剂量等。     

高温气冷堆热气导管中石墨粉尘沉积特性分析

高温气冷堆中石墨粉尘的运动规律对反应堆安全具有重要意义。本工作采用计算流体力学方法得到热气导管中的温度场分布,在此基础上分析了热气导管中热泳沉积与湍流沉积的规律。结果表明,随着颗粒粒径的增大,热泳沉积率下降,而湍流沉积率则先减少后增大。通过比较30%FP及100%FP两种反应堆功率下的计算结果发现：反应堆功率为30%FP时对应的热泳沉积率更高,而反应堆功率为100%FP时,湍流沉积率增长更加迅速。当颗粒粒径较小时,热泳沉积与湍流沉积作用相当,颗粒粒径较大时,湍流沉积明显占主导地位。最后,采用最可几分布的粒径计算了热气导管中石墨粉尘总的沉积量,计算结果表明石墨粉尘沉积总量有限。     

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     

Calculation of the depletion of a radioactive plume in the atmosphere and subsequent exposure due to deposited activity

An efficient method has been developed for calculating the depletion, by dry deposition and washout to the ground, from a plume of fission products in the atmosphere, and for determining the isotopic composition of resulting gamma and beta activities in the ground deposit at any selected point downwind. By integration over the pattern of material on the ground, gamma and beta exposure rates may be derived as a function of the ageing time of the deposit. Elements in the plume are assigned to one of up to four ‘groups’; elements within each group being assigned a particular deposition velocity and washout coefficient.Calculations have been performed, for a notional MAGNOX depressurization accident, which illustrate the sensitivity of ground gamma spectra and exposure rate to the use of isotope-dependent deposition velocities. Circumstances under which it may be necessary to perform a full two-dimensional integration over the pattern of material on the ground are discussed.     

核电厂事故应急局地实时剂量评价系统的模式与参数

本文介绍在核电厂事故应急局地实时剂量评价系统中应用的拉格朗日烟团模式及相应的参数。对烟团轨迹考虑了事故期间风向、风速的变化,采用有效扩散参数以考虑烟团迁移期间大气稳定度等气象条件的变化,干沉积采用源耗减模式,湿沉积采用冲洗系数方法,还考虑了放射性衰变及烟团部分穿透混合层的修正。鉴于我国在建核电厂皆位于沿海地区,文中还给出了内边界层条件下烟团公式的处理方法。对于实时剂量评价,主要考虑了烟云浸没外照射、吸入内照射和沉积放射性核素外照射三种照射途径。最后,以秦山核电厂为例估算了 PWR1事故的环境影响,给出了部分计算结果。     

2MW液态钍基熔盐实验堆气载放射性流出物近场扩散的数值模拟

气载放射性流出物在近场范围内的扩散是核设施环境影响评价研究的重要内容之一,传统的高斯模型由于受到复杂建筑物的影响导致计算结果偏差比较大,不宜用于近场扩散的数值模拟。本文采用计算流体动力学(Computational Fluid Dynamics,CFD)方法以2 MW液态钍基熔盐实验堆的拟定场址为研究对象,开展放射性气态流出物在近场范围内分布规律的研究,分析风速、烟囱高度、风向等参数对气态流出物大气弥散因子分布的影响。结果表明,对于高架排放,由烟羽抬升的影响使得风速越大近场范围的放射性核素大气弥散因子越高;在下风向建筑群迎风侧均易出现放射性核素集聚区,烟囱高度越低集聚现象越明显。本研究的结果可为熔盐堆场区辐射环境影响评价及建筑物的布局、核应急提供参考依据。     

Stoichiometry distribution of thin films deposited by laser ablation: Monte Carlo simulation

An expansion of a bi-component laser plume into a dilute background gas is simulated using a combined Monte Carlo simulation method. The effects of different types of collisions taking place during the transport of the ablated species on their distributions when arriving at a flat substrate are shown. Furthermore, we demonstrate that the film thickness distributions of both components and, hence, the final stoichiometry distribution, depend strongly on the incorporation probability of the species. This probability is expressed as a function of both deposited particle energy and the substrate absorbing properties. These studies can facilitate the comparison of the simulation results with experiments and are of particular interest for pulsed laser deposition (PLD) of multicomponent materials.     

Energy properties and spatial plume profile of ionic liquid ion sources based on an array of porous metal strips

An ionic liquid ion source(ILIS)is a kind of high brightness ion source capable of providing high-speed positive or negative ion beams.This paper presents a miniaturized ILIS based on an array of porous metal strips.The porous emitter array,integrated with seven 10 mm long strips,is fabricated using wire electrical discharge machining(WEDM)combined with electrochemical etching.The assembled ILIS is 30 mm x 30 mm x 17.5 mm in size and weighs less than 25 g.A series of experiments,including an I-V characteristic test,a retarding potential analyzer(RPA)test,and a spatial plume distribution test,have been conducted in vacuo to characterize the performance of the ILIS.Results show that the emitted current is up to about 800 μA and ion transparency is as high as 94％.Besides,RPA curves reveal that the total fragmentation rate of the emitted particles accounts for 48.8％in positive mode and 59.8％in negative mode.Further,with the increase in applied acceleration voltage,the voltage loss rises while the energy efficiency decreases.It is also found that the plume perpendicular to the strips has a higher divergence than the one parallel to the strips.A numerical simulation by COMSOL reveals that the electric field distribution between the two electrodes results in such a spatial plume profile.     

De-agglomeration mechanisms of TiO2 aerosol agglomerates in PWR steam generator tube rupture conditions

A steam generator tube rupture (SGTR) in a pressurized water reactor (PWR) might be a major source of accidental release of radioactive aerosols into the environment during severe accident due to its potential to by-pass the reactor containment. In the ARTIST program, tests were carried out at flow conditions typical to SGTR events to determine the retention of dry aerosol particles inside a steam generator tube. The experiments with TiO₂ agglomerates showed that for high velocities in the range of 100-350 m/s, the average particle size at the outlet of the tube was significantly smaller than at the inlet due to particle de-agglomeration. Earlier, particle de-agglomeration has not been considered significant in nuclear reactor severe accidents. However, the tests in ARTIST program have shown that there is a possibility that TiO₂ aerosol particles de-agglomerate inside a tube and in the expansion zone after the tube exit under SGTR conditions.In this investigation, we measured TiO₂ aerosol de-agglomeration in the tube with very high flow velocities with two different TiO₂ aerosols. The de-agglomeration was determined by measuring the size of the agglomerates at the inlet and outlet of the test section. The test section was composed of tubes with three different lengths, 0.20, 2.0 and 4.0 m, followed by an expansion zone.The main results were: (i) the de-agglomerate process was relatively insensitive to the initial particle size distribution, (ii) the agglomerates were observed to de-agglomerate in all the tubes, and the resulting particle size distributions were similar for both TiO₂ aerosols, (iii) at high flow rates, increasing the gas mass flow rate did not produce further de-agglomeration, and (iv) the agglomerates did not de-agglomerate to primary particles. Instead, after de-agglomeration the particles had a median outer diameter D_c = 1.1 μm. Based on analysis using computational fluid dynamics (CFDs), the de-agglomeration was caused by the turbulent shear stresses due to the fluid velocity difference across the agglomerates in the viscous subrange of turbulence.It has to be noted that the particles used in this investigation were TiO₂ agglomerates, and not prototypical nuclear aerosols with significantly different characteristics. Therefore, the results of this investigation cannot be directly used to determine whether the nuclear aerosol particles may de-agglomerate in SGTR sequences. However, this investigation highlights the possibility of particle de-agglomeration under SGTR conditions, and identifies the mechanism of the de-agglomeration inside the broken tube and when the aerosol is discharged to an open space.     

Analysis of the plasma-particle interaction during the plasma spraying of beryllium

Beryllium plasma-spray technology is being investigated as a method for coating plasma facing surfaces inside the international thermonuclear experimental reactor (ITER). This study investigated the plasma and plasma-particle interactions that occur during the plasma-spraying of beryllium. To evaluate the effect of the chamber pressure on the temperature, velocity, and trajectory profiles of the injected beryllium particles, the particles were numerically analyzed at three operating pressures (i.e., 101.3, 66.6 and 46.6 kPa) under a fixed operating condition. The thermal plasma was numerically modeled to predict the gas dynamics of the plasma column and plume. This information was then used as boundary conditions to solve the plasma—particle interaction problem at the various operating pressures. Calculations were performed for beryllium particles that ranged in diameter between 4 and 38 μm. Results of the numerical simulations describing the particle temperatures, velocities, and trajectories are discussed.     

Measurements of solid particle suspension concentrations in boiling pools

An experimental study was performed to measure vertical particle suspension concentrations in contaminated boiling pools. The study was conducted in a nucleate boiling regime. Tests were conducted with distilled water and solid nickel particles ranging in size from 5 to 40 μm. The test apparatus was 30 cm wide and 120 cm high. Particle concentrations were on the order of milligrams per cubic centimeter of slurry. Heat fluxes on the order of 100 kW m⁻² were attained by electrical bottom heating. Corresponding superficial vapor velocities were on the order of several centimeters per second. Measurements were aimed to reveal the dependence of dilute particle suspension distributions on the pool depth, heat flux and particle loading. The results indicate that only a fraction of the particle loading gets suspended. This fraction turns out to be largely dependent on the pool depth and heat flux, but is insensitive to particle loading variations. The particle distribution within the suspension was analyzed with the dispersion–sedimentation model. The work demonstrates the applicability of this model for the conditions of boiling pools and partial particle suspensions. Furthermore, the results indicate that for shallow pools and small size particles the distributions are fairly uniform. Consequently, the suspension concentration is substantially a function of the fraction suspended. The work provides experimental data to evaluate this fraction for a range of heat fluxes and pool depths. The knowledge of particle suspension concentrations has important industrial and environmental applications in the power generation, nuclear and chemical engineering industries. For example, the results could be used to evaluate the amount of particle released from a contaminated boiling-pool spill, or could be used to reduce conservatism applied in analyses of pools containing larger particles.     

气载碘在农作物、草和土壤中的沉积及其吸收和易位实验研究(英文)

为了深入了解放射性碘在亚洲生物圈中的迁移规律,建立了一个封闭的实验系统,进行气载125I释放后在作物和土壤的沉积和吸收规律实验。盆栽实验的结果表明,(1)125I气溶胶在农作物上的沉积主要是干沉积;(2)沉积在农作物上的125I可以通过叶面吸收转移到其他组织中;(3)玉米和菜豆的易位因子最大。125I从土壤到农作物的吸收实验表明,沉积在土壤中的125I能够通过根部吸收转移到农作物中,125I在小米和高粱中的转移系数明显高于其他作物。