Study of emission episodes of urban aerosols by ion beam analytical techniques

The quantitative elemental composition and morphology of over 500 atmospheric aerosol particles were determined by nuclear microscopy and scanning electron microscopy (SEM). The samples originated from eight sampling campaigns, when hourly variation and sources of the urban aerosol elemental components were studied in Debrecen between 2007 and 2010. Aerosol which could be connected to heavy metal pollution episodes and high aerosol pollution levels deposits were selected for the nuclear microprobe study.Ion beam analytical methods (micro-PIXE and STIM) provided the elemental composition of coarse (particles with aerodynamic diameter between 2.5 and 10 μm) aerosols while the morphology of the different particle types was determined by SEM.Through the elemental composition, elemental correlations and morphology different particle types were identified and attributed to different anthropogenic sources like biomass burning, oil combustion, traffic or industry.     

Size-fractionated aerosol composition during an intensive 1997 summer field campaign in northern Finland

A 12-stage small deposit area low pressure impactor (SDI) was used to collect size-fractionated aerosol samples during an intensive 1997 summer field campaign in northern Finland. The samples were analyzed for over 20 elements by PIXE, and some “difficult” elements such as As and Se could be quantified. The sea-salt and crustal elements had essentially a unimodal coarse size distribution with geometric mean aerodynamic diameter (GMAD) of about 4–5 μm. In one third of the samples, S showed only one mode in the fine size range, with GMAD of 0.4–0.5 μm. In the other samples, this fine S mode broke up into two modes, with GMADs of 0.3 and 0.6 μm, respectively. V, Zn, As, Se and Pb were mainly present in a single submicrometer mode, with GMAD of 0.4–0.5 μm for V and Se, and slightly larger (i.e., 0.6 μm) for the other three elements. The highest concentrations of S, V, Ni, Cu, Zn, As, Se and Pb were encountered in the SDI sample which had been collected in the period 14–16 July. During this sampling, the air masses came in from the west, but had recirculated over northern Scandinavia and passed over the Kola peninsula.     

秦山核电厂气态流出物气溶胶粒径分布测量

对秦山核电基地烟囱流出物的粒径分布谱进行了实验测量,结果表明:气态流出物中的气溶胶粒径大多在1 μm以下,但总粒子数浓度随机组类型不同而不同。测量结果为评估核电厂气态流出物监测系统采样的有效性提供了参考。     

Dryout heat flux experiments with deep heterogeneous particle bed

A test facility has been constructed at Technical Research Centre of Finland (VTT) to simulate as accurately as possible the ex-vessel core particle bed in the conditions of Olkiluoto nuclear power plant. The STYX particle bed reproduces the anticipated depth of the bed and the size range of particles having irregular shape. The bed is immersed in water, creating top flooding conditions, and internally heated by an array of electrical resistance heating elements. Dryout tests have been successfully conducted at 0.1–0.7 MPa pressure for both uniformly mixed and stratified bed geometries. In all tests, including the stratified ones, the dry zone first formed near the bottom of the bed. The measured dryout heat fluxes increased with increasing pressure, from 232 kW/m² at near atmospheric pressure to 451 kW/m² at 0.7 MPa pressure. The data show some scatter even for the uniform bed. The tests with the stratified bed indicate a clear reduction of critical power due to the presence of a layer of small particles on top of the uniform bed. Comparison of data with various critical power (dryout heat flux) correlations for porous media shows that the most important parameter in the models is the effective particle diameter. Adiabatic debris bed flow resistance measurements were conducted to determine the most representative particle diameter. This diameter is close, but not equal, to the particle number-weighted average diameter of the bed material. With it, uniform bed data can be calculated to within an accuracy of 3–28% using Lipinski's 0-D model. In the stratified bed experiments, it appears that the top layer was partially fluidized, hence the measured critical power was significantly higher than calculated. Future experiments are being planned with denser top layer material to eliminate non-prototypic fluidization.     

The aerosol release factor for Pu as a consequence of an ion exchange resin fire in the process cell of a fuel reprocessing plant

One of the upper limit accidents usually considered in the safety analysis of a fuel reprocessing plant is an accidental explosion, followed by a fire, of an ion exchange column containing resin loaded with large quantities of plutonium. In such accidents, a certain fraction (release factor) of Pu is released in the form of an aerosol into the ventilation system, and finally to the environment through HEPA filters and the stack. The present study was undertaken to determine the aerosol release factor for Pu in the process cell of a typical fuel reprocessing plant.Geometrically similar scaled-down models of three different sizes were built, and suitably scaled-down quantities of resin loaded with thorium in nitric acid medium were burnt in these model cells. Thorium was used in place of Pu because of its physical and chemical similarities with Pu. The release factor was obtained by comparing the amount of Th in air with the total. The study also dealt with aerosol characteristics and kinematics of process of fire.The aerosol release factors for the three models were found to lie in the range 0.01–0.07%, and varied non-monotonically with model size. The analysis of scaled down results in conjunction with simplified aerosol modelling yielded the release factor for the actual cell conditions as 0.012% with an upper limit value of 0.1%. The particle size analysis based on Th-radioactivity and particle-mass indicated nonuniform tagging of Th to aerosol particles. These particles were irregularly shaped, but not as long chain-like aggregates.The study proposes, with a reasonable degree of conservatism, the release factor of 0.1% for such fires, and aerosol parameters, AMAD and σ_g, as 2 μm and 2 respectively. However, for situations significantly different from the present one, the release factor of 1% recommended by the American National Standards Institute may be used with a greater degree of confidence in the light of the present work.     

Observation of Radioactive Aerosol Emissions from the Sarcophagus at the Chernobyl Nuclear Power Plant

It is shown that high wind velocity outdoors results in a higher concentration of radioactive aerosols in the ventillation exhaust from the sarcophagus. Aerosol samples from manholes in the roof of the sarcophagus have been collected, for the first time ever, in January–December 2002 on trilayer filter packets. The ¹³⁷Cs concentration in outgoing flows is 0.7–2.3 Bq/m³. The activity median aerodynamic diameter of the aerosol carrier particles is 0.7–1.8 m. At the same time, the ¹³⁷Cs concentration in the atomspheric layer at the ground dear the sarcophagus was 1000 times lower and the carrier-particle sizes 2–4 times larger.     

Hydrodynamics of degraded core cooling

The literature on hydrodynamics of forced convection cooling of particle beds is reviewed and used to assess the characteristics of in-situ cooling of a degraded LWR reactor core under conditions representative of severe accidents. It is found that the pressure head required, for a given rate of liquid water flow, through a totally degraded core is one to two orders of magnitude higher than the case of intact core geometry. To remove decay heat of up to 1–2% of the reactor normal power, even with conservative assumptions, the pressure head is within the capability of the main reactor pumps. However, particles with very small diameter (less than 100 μm) will potentially be swept out by the flow. The sensitivity of the hydraulic characteristics to the allowed coolant temperature rise across the fragmented core is also investigated.     

Methods for Determining the Distribution Function for the Radius of Uranyl-fluoride Aerosol Particles

A system of uranyl-fluoride aerosol particles is studied to determine the particle radius distribution function. The particles are formed during hydrolysis of uranium hexafluoride in the air in working rooms at enterprises of the atomic industry. An analytical expression is obtained for the distribution function of the radius of aerosol particles at the moment the particles are created under the conditions of one-time emission and for everyday working conditions as a function of the coordinates of the volume considered and the air-exchange ratio. It is shown that on changing to an air-exchange regime the dependence of the distribution function on the partice radius changes. The distribution functions found are used to determine the median aerodynamic diameter, making it possible to estimate the retention factor for aerosol particles in various parts of the respiratory tract. __________ Translated from Atomnaya Energiya, Vol. 99, No. 5, pp. 353–358, November, 2005.     

阳江核电厂外围环境气溶胶总α、总β放射性水平

核电厂周围环境气溶胶的总放射性水平是一项重点关注项目。为掌握阳江核电周围环境气溶胶中总α、总β放射性水平及变化趋势,自2014年1月,对阳江核电厂5 km范围内大澳和允泊的气溶胶总α、总β进行为期三年的采样监测,获得该核电厂5 km范围内气溶胶总α、总β活度浓度范围分别为0.01-0.35 m Bq·m~(-3)、0.05-2.46 m Bq·m~(-3),年均值分别为0.07 m Bq·m~(-3)、0.65 m Bq·m~(-3)。受降雨影响,总α、总β放射性变化有明显的季节特征,总体呈现冬春季高、夏秋季低的特点。监测结果与对照点和本底调查进行比较,总α、总β活度浓度没有明显变化,初步判断阳江核电厂运行安全。     

Performance analysis of coated plutonia particle fuel compact for radioisotope heater units

Coated plutonia particle fuel has been proposed recently for use in radioisotope power systems and radioisotope heater units for a variety of space missions requiring power levels from milliwatts to tens or even hundreds of watts. The ²³⁸PuO₂ fuel kernels are coated with a strong layer of ZrC designed to fully retain the helium gas generated by the radioactive decay of ²³⁸Pu. A recent investigation has concluded that helium retention in large-grain (200 μm) granular and polycrystalline fuel kernels is possible even at high-temperatures (>1700 K). Results of performance analysis showed that this fuel form could increase by 2.3–2.4 times the thermal power output of a light weight radioisotope heater unit. These figures are for a single-size (500 μm) particles compact, assuming 10% and 5% helium gas release respectively, and a fuel temperature of 1723 K, following 10 years of storage. A binary-size (300 and 1200 μm) particles compact increases the thermal power output of the RHU by an additional 15%.     

Origin and Components of Radioactive Aerosols on the Cover Site at the Chernobyl Nuclear Power Plant

It is shown that essentially three sources determine the ¹³⁷Cs concentration in aerosols at the site of the object Cover at the Chernobyl nuclear power plant: a natural source (global transport of air masses and local wind uplift of dust) and two technogenic sources (work performed at the industrial site and operation of the object). Continual aerosol sampling for two weeks at the site in 2000 using FPP-15-1,5 filters shows that the ¹³⁷Cs/²⁴¹Am ratio remained in the range 50–70. This shows that during that period the artificial radioactive aerosols resulted from work performed at the site and wind uplift. The effect of work performed inside the object Cover on the aerosol conditions around the object is studied for the fire which occurred on January 14, 1993 in room 805/3.     

Study of particulate emissions near a steel plant in Genova by continuous sampling and PIXE hourly analysis

The particulate emissions near a large steel plant located in a densely inhabited suburb of the town of Genova (Italy) have been studied for a period of six months. We have used two-stage continuous streaker samplers and subsequent PIXE analysis with hourly resolution, to follow both seasonal and daily trends. The first streaker sampler remained installed very close to the plant cokery and furnaces, while another sampler was moved to different locations. Samples have been analysed by PIXE, deducing concentrations for elements from Na to Pb. During part of the campaign, the aerosol fractions with aerodynamic diameter (D_ae) < 2.5 μm (fine fraction) and with 2.5 < D_ae < 10 μm (coarse fraction) have been separately collected. We have measured and analysed about 8500 PIXE spectra: the steel plant emissions have been identified to some extent and resolved from other aerosol sources.     

Aerosol composition and source apportionment in Santiago de Chile

Santiago de Chile, São Paulo and Mexico City are Latin American urban areas that suffer from heavy air pollution. In order to study air pollution in Santiago area, an aerosol source apportionment study was designed to measure ambient aerosol composition and size distribution for two downtown sampling sites in Santiago. The aerosol monitoring stations were operated in Gotuzo and Las Condes during July and August 1996. The study employed stacked filter units (SFU) for aerosol sampling, collecting fine mode aerosol (dp<2 μm) and coarse mode aerosol (210 mass of particles smaller than 10 μm) and black carbon concentration were also measured. Particle-Induced X-ray Emission (PIXE) was used to measure the concentration of 22 trace elements at levels below 0.5 ng m⁻³. Quantitative aerosol source apportionment was performed using Absolute Principal Factor Analysis (APFA). Very high aerosol concentrations were observed (up to 400 μg/m³ PM₁₀). The main aerosol particle sources in Santiago are resuspended soil dust and traffic emissions. Coarse particles account for 63% of PM₁₀ aerosol in Gotuzo and 53% in Las Condes. A major part of this component is resuspended soil dust. In the fine fraction, resuspended soil dust accounts for 15% of fine mass, and the aerosols associated with transportation activities account for a high 64% of the fine particle mass. Sulfate particle is an important component of the aerosol in Santiago, mainly originating from gas-to-particle conversion from SO₂. In the Gotuzo site, sulfates are the highest aerosol component, accounting for 64.5% of fine mass. Direct traffic emissions are generally mixed with resuspended soil dust. It is difficult to separate the two components, because the soil dust in downtown Santiago is contaminated with Pb, Br, Cl, and other heavy metals that are also tracers for traffic emissions. Residual oil combustion is observed, with the presence of V, S and Ni. An aerosol components from industrial emissions is also present, with the presence of several heavy metals such as Zn, Cu and others. A factor with molybdenum, arsenic, copper and sulfur was observed frequently, and it results from emissions of copper smelters.     

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.     

ARTIST: introduction and first results

Aerosol Trapping In a Steam Generator (ARTIST) is a seven-phase international project (2003–2007) which investigates aerosol and droplet retention in a model steam generator under dry, wet and accident management conditions, respectively. The test section is comprised of a scaled steam generator tube bundle consisting of 270 tubes and three stages, one 1:1 separator unit, and one 1:1 dryer unit.As a prelude to the ARTIST project, four tests are conducted in the ARTIST bundle within the 5th EU FWP SGTR. These first tests address aerosol deposition phenomena on two different scales: near the tube break, where the gas velocities are sonic, and far away from the break, where the flow velocities are three orders of magnitude lower. With a dry bundle and the full flow representing the break stage conditions, there is strong evidence that the TiO₂ aerosols used (AMMD 2–4 μm, 32 nm primary particles) disintegrate into much smaller particles because of the sonic conditions at the break, hence promoting particle escape from the secondary and lowering the overall DF, which is found to be between 2.5 and 3. With a dry bundle and a small flow reproducing the far-field velocities, the overall bundle DF is of the order of 5, implying a DF of about 1.9 per stage.Extrapolating the results of the dry tests, it turns out that for steam generators with nine or more stages, it is expected that substantial DF’s could be achieved when the break is located near the tube sheet region. In addition, better decontamination is expected using more representative proxies of severe accident aerosols (sticky, multi-component particles), a topic which is yet to be investigated.When the bundle is flooded, the DF is between 45 and 5740, depending on the mass flow rate, the steam content, and the water submergence. The presence of steam in the carrier gas and subsequent condensation inside the broken tube causes aerosol deposition and blockages near the break, leading to an increase in the primary pressure. This has implications for real plant conditions, as aerosol deposits inside the broken tube will cause more flow to be diverted to the intact tubes, with a corresponding reduction in the source term to the secondary.     

On the nature of aerosols produced during a severe accident of a water-cooled nuclear reactor

Particle behaviour depends strongly on classic characteristics, e.g., size, and less macroscopic ones involving structure and composition these being especially important in situations of strong differential forces on a particle, i.e., surface impact or intensely-shearing flows. The former situation may lead to particle deposition or break-up and re-entrainment (with potential accident-management implications). This paper reviews information on aerosols from prototypical experiments identifying common features and typical variations. It emerges that a particle comprising one-third metal, one-third metal oxide and one-third a mixture of fission-product species would not be out of place in any potential reactor-accident sequence. Particle shapes appear relatively compact without branching chain-like structures. On size and structure, aerosols in the upstream part of the primary circuit would comprise a near-lognormal population with AMMD no more than 2 μm and geometric standard deviation around 2, particles comprising agglomerates of highly-coordinated clusters as small as 0.1 μm. In the containment, aerosols can typically be represented by primary-circuit particles and their agglomerates though particular circumstances (core–concrete interaction, hot-leg accident sequence) can alter this simple picture.     

Fires in large scale ventilation systems

This paper summarizes the experience gained simulating fires in large scale ventilation systems patterned after ventilation systems found in nuclear fuel cycle facilities. The series of experiements discussed includes: (1) combustion aerosol loading of 0.61×0.61m HEPA filters with the combustion products of two organic fuels, polysterene and polymethylemethacrylate; (2) gas dynamic and heat transport through a large scale ventilation system consisting of a 0.61 m duct 90 m in length, with dampers, HEPA filters, blowers, etc.; (3) gas dynamic and simultaneous transport of heat and solid particulate (consisting of glass beads with a mean aerodynamic diameter of 10μ) through the large scale ventilation system; and (4) the transport of heat and soot, generated by kerosene pool fires, through the large scale ventilation system.The FIRAC computer code, designed to predict fire-induced transients in nuclear fuel cycle facility ventilation systems, was used to predict the results of experiments (2) through (4). In general, the results of the predictions were satisfactory. The code predictions for the gas dynamics, heat transport, and particulate transport and deposition were within 10% of the experimentally measured values. However, the code was less successful in predicting the amount of soot generation from kerosene pool fires, probably due to the fire module of the code being a one-dimensional zone model. The experiments revealed a complicated three-dimensional combustion pattern within the fire room of the ventilation system. Further refinement of the fire module within FIRAC is needed.     

钚气溶胶的形成机理

核科学研究、核电站事故与核恐怖袭击释放的钚气溶胶,是一种危害公众与环境安全的毒性材料。掌握钚气溶胶的形成机理,不仅是评估和预防其辐射影响的理论基础,而且是钚气溶胶采样、特性分析等工作的重要前提。本文依据气溶胶粒子三种模态分布理论,总结了钚气溶胶形成过程中的气相成核与凝结凝聚两个控制步骤,综述了氧化、燃烧、高能事件等不同场景下的钚材料气溶胶化的形成机理,包括钚气溶胶形成时的化学过程研究进展,以期对后续的相关研究工作有帮助。     

核电厂蒸汽发生器传热管氦气检漏系统研究

本研究介绍了某核电厂蒸汽发生器传热管在役氦气检漏系统的原理及系统组成,并模拟了某核电厂蒸汽发生器在役大修期间传热管检漏试验。试验结果表明,最佳参数可设置为:蒸汽发生器二次侧氦气浓度份额为30%;抽气速率为 20 L/min;蒸汽发生器二次侧压力为0.6 MPa;系统漏点定位误差在0.5 m以内。本文研究的蒸汽发生器传热管在役氦气检漏系统可为国内核电厂安全、稳定地运行提供可靠的技术保障。      

Meeting the energy challenge for the environment: The role of safety

Nuclear power has an overwhelming potential to meet the demands of an energy hungry world while protecting the environment. However, the renaissance of nuclear energy will only become true when the public can be convinced that nuclear power plants are safe and that a strong safety culture exists around the globe. While the overall safety performance of the world's power plants had been steadily improved after the shock of Chernobyl, unfortunately, the overall plant availability has levelled off in the last few years. The main reason for this is found in a complacency toward nuclear safety issues which can be linked to the arrival of new CEOs in the nuclear industry who – all too often – have no nuclear background and who manage nuclear power plants in the same way they would manage any other industrial plants – being not at all aware of the necessity of a very special and very sensitive safety culture of nuclear installations.