Study of individual atmospheric aerosol particles at the Debrecen ion microprobe

Aerosol samples collected in outside and indoor environments with a 9-stage PI cascade impactor were analysed using PIXE, STIM (on and off-axis) and RBS ion beam analytical techniques at the Debrecen ion microprobe. Elemental composition, size and morphology of single aerosol particles were determined.Since the quantitative determination of light element concentrations requires a support material with small or no light element content, impactor surfaces made of different materials were tested in order to optimize the sampling and analysis. Thin polymer and Al foils were found to be possibly adequate substrate materials.     

佩戴防尘口罩对吸入气溶胶粒度影响的实验研究

本文介绍了应用级联撞击器和佩戴口罩的人头模型在天然铀燃料元件加工现场测定吸入气溶胶粒度的方法。结果表明,佩戴口罩使得吸入气溶胶的活度中值空气动力学直径(AMAD)变小,并且吸入气溶胶的 AMAD 值与场所气溶胶的 AMAD 值有一定关系,粒径分布类型也发生改变。文中还报告了口罩的漏过率有随微尘粒径减小而增大的趋势。实验结果对内照射剂量估算以及评价口罩的防尘能力有一定的参考价值。     

Modeling analyses of radioactive aerosol flow and collection in mesoscopic impactor filters

The concentration of radioactive aerosols in the containment increases rapidly during the serious nuclear accidents. The common aerosol filters use mesh structures or filter papers, which can significantly increase the flow resistance due to the aerosol deposition and retard the containment pressure relief following the nuclear accidents. This paper proposes and studies a MEMS (Micro Electro Mechanical Systems) inertial impactor filters which can filtrate and collect 1 to 3 microns aerosol particles without filter papers. It can significantly reduce the flow resistance in filtering micron-size aerosol particles. The modeling method is given and the simulation results are analyzed.     

微流体惯性冲击器过滤性能模拟计算

用微流体惯性冲击器收集μm尺寸气溶胶颗粒是一种新型的过滤方式,弥补了现有过滤收集方式的不足,已有学者进行了可行性论证,但气流在现有的T型惯性冲击器内压力损失较大且冲击器的加工工艺较为繁琐。本文设计并研究了一种新型微流体惯性冲击器,采用CFD软件对微流体惯性冲击器的过滤性能进行了数值模拟。建立了数学模型,对气相采用层流模型,对颗粒相采用离散相模型(DPM)。通过模拟计算,分析了不同尺寸的微流体惯性冲击器对粒子收集效率的影响。结果表明,冲击器转折角和尺寸D对收集效率均有较大影响:转折角越小,收集效率越高;当D≤1/2时,效率曲线基本不变。     

Quantitative analysis of cascade impactor samples – revisited

Concentrations of aerosols collected in Singapore during the three months long haze period that affected the whole South-East Asian region in 1997 are reported. Aerosol samples were continuously collected by using a fine aerosol sampler (PM2.5) and occasionally with a single orifice cascade impactor (CI) sampler. Our results show that in the fine fraction (<2.5 μm) the concentrations of two well-known biomass burning products, i.e. K and S were generally increased by a factor 2–3 compared to the non-hazy periods. However, a discrepancy was noticed, at least for elements with lower atomic number (Ti and below) between the results obtained by the fine aerosol sampler and the cascade impactor. Careful analysis by means of Nuclear Microscopy, in particular by the Scanning Transmission Ion Microscopy (STIM) technique, revealed that thicknesses of the lower CI stages exceeded thick target limits for 2 MeV protons. Detailed depth profiles of all CI stages were therefore measured using the STIM technique and concentrations corrected for absorption and proton energy loss. After correcting results for the actual sample thickness, concentrations of all major elements (S, Cl, K, Ca) agreed much better with the PM2.5 results. The importance of implementing thick target corrections in analysis of CI samples, especially those collected in the urban environments, is emphasized. Broad beam PIXE analysis approach is certainly not adequate in these cases.     

MAPPIX: A software package for off-line micro-pixe single particle aerosol analysis

In the framework of a multiannual experiment performed at Baia Terra Nova, Antarctica, size-segregated aerosol samples were collected by using a 12-stage SDI impactor (Hillamo design). Approximately 2800 particles, belonging to the first four supermicrometric SDI stages – 8.39, 4.08, 2.68, 1.66 μm dynamic aerosol diameter cuts – were analyzed at the INFN-LNL micro-PIXE facility, a three lens Oxford Microprobe (OM) product, installed in the early nineties. Four regions on each of the 12 sub-samples were measured; 60 aerosol particles were detected on average in each of the analyzed regions.The off-line single aerosol particle (SAP) analysis of such big amount of data required software that is able to rapidly handle the acquired data, with a simple and fast area selection procedure; the subsequent automated PIXE spectra analysis with a specialized code was also needed.The MAPPIX 2.0 software was designed to make easier and faster the user jobs during the SAP analysis. The package is composed of two separate routines: the first one is devoted to data format conversion (OM-LMF file format to MAPPIX format), while the second one is devoted to micro-PIXE maps graphical presentation and aerosol particle selection procedure.The MAPPIX data format and software features will be discussed; a short report of the speed performances will be presented.     

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.     

Use of rutherford scattering on a secondary carbon target for correcting intermediate thickness sample PIXE measurements

A method is presented for correcting PIXE measurements on intermediate thickness targets. The correction deals with the X-ray attenuation and the incident proton energy loss. It is based on the simultaneous acquisition of the PIXE spectrum along with the energy distribution of protons elastically scattered by a thin secondary carbon foil located behind the PIXE target. These measurements allowed a linear correlation between the proton energy loss ΔE and the correcting factor for X-ray absorption XF to be demonstrated.The validity of these simplifying linear approximations is discussed. The method is applicable to inhomogeneous thickness samples like aerosol impactor stages.     

级联撞击器应用中的几个问题

本文对多圆孔式级联撞击器在用于铀燃料元件厂现场放射性气溶胶粒度分析中应予注意的几个问题进行了考察。主要是级联撞击器的壁损失、硫化锌截留平面计数效率的校正及几种截留平面材料性能的比较。     

The fracture and aerosol release of impacted HLW-glasses due to accidental canister drops in a disposal site

For the disposal of HLW-canisters in a salt dome, two different accident scenarios have to be considered, canister drops in the reloading hall or in a borehole with drop heights of 10 m and 600 m, and reference drop velocities of 14 m/s and 80 m/s.The experimental program had two parts:

&#x02022; - Laboratory scale drop tests with bare and canistered waste glass probes (scale: 1:10) to obtain basic data.

&#x02022; - Full scale drop tests with inactive HLW-canisters, specified as planned for the German salt repository (H = 1.335 m, Ø = 0.43 m, weight: 550 kg, canister: SST 1.4833, wall: 5 mm).

The size distributions of the broken fines were measured by sieving and those of the filtered airborne particles by particle size analysis. The dominating parameter is the impact velocity (i.e. impact energy), further test parameters show no measurable influence, especially the canister influence on the fracture or aerosol release is negligible.Source terms, evaluated for the respirable fraction (particles with d < 10 μ m are between 2 × 10⁻⁴% for a 10 m drop and 0.1% for a 600 m borehole drop.     

Chemical speciation of chlorine in particulate matter by wavelength-dispersive PIXE technique

Chemical speciation of chlorine (Cl) in atmospheric particulate matter (APM) was performed by using a wavelength-dispersive PIXE spectrograph based on high-resolution measurement of Cl-Kβ emission. Samples of atmospheric particles were size-fractioned and collected by a cascade impactor at an urban area in Tokyo. The target position with respect to the spectrograph was precisely adjusted by a 2D laser displacement sensor to achieve high detection efficiency. The samples were irradiated with 2 MeV protons from a tandem electrostatic accelerator. The beam current was 300-500 nA. During the irradiation, the target was cooled by liquid nitrogen to avoid the evaporation of volatile Cl compounds. The measured spectra for the NaCl standard samples clearly showed the Cl-Kβ series composed of the Kβ₁ and the satellite Kβ_x, Kβ₅ lines. From the measured X-ray yields, it was found that the chemical speciation of samples with Cl concentrations as low as ≈1% is possible by this method. The Cl-Kβ series were also successfully observed in the case of APM samples with particle sizes of 11.0-2.1 μm. The spectra shapes of the NaCl standard samples and an APM sample were slightly different from each other, because of some possible mixing of non-sea salt component in the APM sample.     

Deuteron–nucleus total reaction cross sections up to 1 GeV

Total reaction cross sections of deuteron, σ^R_d, are calculated by a microscopic three-body reaction model. The reaction model has no free adjustable parameter and applicable to reactions at various deuteron incident energies E_d and with both stable and unstable nuclei. The predicted σ^R_d are consistent with those evaluated by a phenomenological optical potential for E_d ? 200 MeV in which the potential has been parametrized. A simple formula of σ^R_d up to E_d = 1 GeV, as a function of E_d, the target mass number A and its atomic number Z, is given.     

Single Scattering Calculations of Sky-Shine with Cylindrical Container Penetrations

Loss by deposition of aerosol particles in an air sampling pipe causes error in the estimation of aerosol concentration in the atmosphere.

For a horizontal pipe, the deposition fraction for laminar flow can be estimated by equations of deposition governed by gravity settling and diffusion. For turbulent flow, there are two methods available—one using the equation by Yoshioka et al, to express deposition velocity, the other being the “extrapolation method” proposed by the present authors.

The present paper examines the validity of the two methods, with particular reference to the contribution of gravity settling to the deposition, and the effect of roughness of the pipe wall on the deposition from turbulent flow.

The deposition fraction in a horizontal straight metal pipe can be estimated with deviation from experimental values not exceeding a factor of 2, throughout the whole region covered by the study, extending over both laminar and turbulent ranges. Use of a suitable friction factor to account for the roughness of the pipe wall gives a reasonable value of deposition fraction in the turbulent region. The deposition from turbulent flow is mainly governed by gravity settling when the Reynolds number is not very large (Re?10⁴).     

大气气溶胶中7Be的粒径分布

利用5级大流量串级撞击器采集大气气溶胶样品,高纯锗γ谱仪系统测量放射性,分析了大气气溶胶中放射性核素⁷Be的浓度及粒径分布规律。在样品采集期间,环境大气中⁷Be浓度平均值为7.29 mBq/m³,且在春季出现较大的浓度。研究发现,在粒径＞3.0 μm的气溶胶样品中,基本测量不到⁷Be;在粒径＞0.95 μm的气溶胶样品中,⁷Be仅占总量的10%左右;⁷Be主要分布在粒径＜0.95 μm的气溶胶粒子上。     

Aerosol,Gas, and Swarf Production during Underwater Cutting of Reactor Core Internals Using Electron Discharge Machining

Secondary products (aerosol, gas and swarf) are released in the work area when cutting nuclear reactor components are underwater during component replacement. We studied the characteristics and behavior of the secondary products produced during cutting of highly radioactive metals using electric discharge machinery (EDM) underwater. The ratio of the weight of the aerosol produced to the melted weight of a workpiece that was cut using EDM, both with a Ag/W alloy electrode and a carbon electrode, was about 1 × 10^?3. The aerosol had a high concentration of manganese with a high vapor pressure. The production ratio was expressed as the aerosol production rate (ppm) = ?4:6 × 10^?2 Tb + 1:4 × 10² (Tb: boiling point (K)). The EDM cutting produced metal vapors which condensed into particles. Air-borne nickel carbonyl was produced during the EDM cutting of nickel and carbon monoxide with a carbon electrode, and a high efficiency particulate air filter and a charcoal filter were used effectively. In the case of a Ag/W electrode, the swarf contained oxide particles of around 20 mm and hydroxide particles with a diameter of around 10 mm. The water clean-up system was able to purify water with over 95% filtration efficiency using a 1 μm pore-pleated filter cartridge.     

Thermal-Neutron Capture Cross Section and Resonance Integral of Americium-241

The thermal-neutron capture cross section (σ_0;g) and the resonance integral (I _0,g) leading to the ground state of 242Am were measured by an activation method for neutron capture by²⁴¹ Am. A method with gadolinium, which was similar to the cadmium difference method, was used to measure the cross section σ_0;g with attention to resonances of²⁴¹ Am. Americium chloride samples containing²⁴¹ Am radioisotope were irradiated for 68 h in the long-irradiation plug of the Kyoto University Research Reactor, KUR. Wires of Co/Al and Au/Al alloys were used as monitors to determine thermal-neutron fluxes and epithermal Westcott's indexes at the irradiation positions. An α-ray spectrometer was used to measure the activity ratios of²⁴² Cm to²⁴¹ Am. On the basis of Westcott's convention, the σ_0;g and I _0,g values were determined as 628 ± 22 b and 3:5 ± 0:3 kb, respectively.     

Energy Dependence of MeV He+ Ion-Induced Re-Emission of Hydrogen Isotopes Implanted into Graphite

The energy dependence of MeV He⁺ ion-induced re-emission of hydrogen isotopes (H and D) implanted into graphite has been measured by means of the elastic recoil detection (ERD) technique in order to clarify the collision process for the ion-induced detrapping. The experimental re-emission profiles have been analyzed by solving the mass balance equations, in which the ion-induced detrapping cross section σ _d and the rate constants of the retrapping Σ ^T and local molecular recombination K between an activated hydrogen atom and a trapped one are taken into account. The values of σ _d and K/Σ _T have been determined from the best-fit analytical solution to the experimental re-emission profiles. It has been found that the average values of σ _d and K/Σ _T for H are twice as large as those for D, which is the so-called isotope effect.

It has been shown that the experimental values of σ _d and their energy dependence agree well with the theoretical ones, which are calculated using the power-law approximations for Thomas-Fermi potential, on the assumption that the ion-induced detrapping of hydrogen isotopes takes place due to elastic displacement collisions with energetic carbon recoils produced by incident MeV He⁺ ions.     

Behavior of Sodium Oxide Aerosol in a Closed Chamber

The behavior of sodium oxide aerosol in a closed chamber was studied for the safety analysis of a Na-cooled fast reactor. The experimental apparatus and techniques are first described. The aerosol was released during a short time by blowing air onto heated Na in a 1 m³ chamber. The maximum mass concentration of the aerosol in the form of Na₂O ranged of 0.05 ～ 10g/m³. The particle size distribution, the aerosol mass concentration and the mass deposition rates were measured as a function of time.

It was found that the mass median diameter of the aerosol was related to the maximum mass concentration. To determine the character of the behavior of sodium oxide aerosol in the chamber, the density of the aerosol material and the thickness of the boundary layer through which the particles deposit on the chamber wall were observed. The initial half-time of the aerosol mass concentration was compared with the values numerically calculated under certain assumptions.     

The Effect of Grain Size on the Tensile Properties of Magnox AL80

Tensile tests were made on wires of Magnox AL80, Mg-Al alloy and unalloyed magnesium at room and liquid nitrogen temperatures. The grain size dependence of the yield and ultimate tensile stresses were investigated.

It was found that the Petch relationship, σ _y =σ₀+kd ^-1/2, was satisfied even for specimens as slender as 1 or 2 mm diameter, though definite values of σ₀ and k were not obtained. It is thought that the preferred orientation in the wire has an influence on both σ₀ and k. Similar results were also obtained for ultimate tensile stress.

The strain rate dependence of the yield and ultimate tensile stresses were also investigated.     

Strength Degradation of Oxidized Graphite Support Column in VHTR

Air-ingress events caused by large pipe breaks are important accidents considered in the design of Very High Temperature Gas-Cooled Reactors (VHTRs). A main safety concern for this type of event is the possibility of core collapse following the failure of the graphite support column, which can be oxidized by ingressed air. In this study, the main target is to predict the strength of the oxidized graphite support column. Through compression tests for fresh and oxidized graphite columns, the compressive strength of IG-110 was obtained. The buckling strength of the IG-110 column is expressed using the following empirical straight-line formula: σ _cr,buckling = 91.34—1.01 (L/r). Graphite oxidation in Zone 1 is volume reaction and that in Zone 3 is surface reaction. We notice that the ultimate strength of the graphite column oxidized in Zones 1 and 3 only depends on the slenderness ratio and bulk density. Its strength degradation oxidized in Zone 1 is expressed in the following nondimensional form: σ/σ₀ = exp(—kd), k = 0.114. We found that the strength degradation of a graphite column, oxidized in Zone 3, follows the above buckling empirical formula as the slenderness of the column changes.