Deposition Of Radioactive Particles Research Articles

A study of particle dry deposition parameterizations in an atmospheric radioactive preparedness model: Application to the Chernobyl case

Parameterization of dry deposition is key for modelling of atmospheric transport and deposition of radioactive particles. Still, very simple parameterizations are often encountered in radioactive preparedness models such as the SNAP model (SNAP=Severe Nuclear Accident Program) of the Norwegian Meteorological Institute. In SNAP a constant dry deposition velocity (=0.2 cm/s) neglecting aerodynamic and surface resistances, is presently used. Therefore, two new dry depositions schemes (the Emerson scheme and the EMEP (European Monitoring and Evaluation Programme) scheme) have been implemented in SNAP to evaluate the benefits of including aerodynamic and surface resistances codes with respect to model prediction skills. The three dry deposition schemes are evaluated using 137Cs total deposition from soil sample data (n = 540) for a 60 km radial zone out from the Chernobyl Nuclear Power Plant (ChNPP) collected during the months after the accident. The present study capitalizes on high resolution meteorological data (2.5 km horizontal resolution), a detailed land-use data set with 273 sub-classes and the hitherto most comprehensive source term description for the Chernobyl accident. Based on our findings it is recommended to replace the present simple SNAP scheme with the Emerson or EMEP dry deposition scheme.

Size distribution of ambient and radioactive aerosols formed by the short-lived radon progeny

The survey of ambient airborne particle size distribution is important when the deposition of radioactive particles is considered in the human lung and the assessment of radiation hazard in occupational exposures or contaminated environments. CLOR (the Central Laboratory for Radiological Protection) in cooperation with CMI (the Central Mining Institute) performed simultaneous measurements of the activity size distribution of radon progeny and ambient aerosols using different types of aerosols. Measurements were performed in a radon chamber with a volume of 17 m3, where radon was generated by a radium-226 open source, and ambient aerosols by an oil candle, vax candle, and incense sticks. Such measurements were also made in an aerosol depleted atmosphere after cleaning the chamber air by means of a high-efficiency pump and filters. The size distribution of radioactive aerosols containing radon progeny was measured by RPPSS (Radon Progeny Particle Size Spectrometer) with the measuring size ranging from 0.6 nm to approximately 2500 nm. The key parts of this device are the impaction plates and diffusion screen batteries, which collect aerosols of different sizes, and semiconductor alpha detectors which detect the activity of the collected particles. The SMPS (Scanning Mobility Particle Sizer Spectrometer) and APS (Aerodynamic Particle Sizer) were applied to evaluate the size distribution of all aerosols with sizes from approximately 3 nm to 20 μm. Based on the results obtained by these spectrometers, the activity size distributions and related dose conversion factors (DCF) were evaluated both for the exposed workers and the general population.

Environmental behaviour of radioactive particles: Transfer to animals

Field data on behaviour of artificial polydisperse radioactive silica particles in the components of the cattle food chain are presented. The model fused radioactive particles reproduced the spherical shape of particles in the local deposition during nuclear tests, including their specific gravity and polydispersity. It is shown that the composition of radioactive particles entering the body of animals differs from those initially deposited on the surface of pasture grass. The intake of particles into the body of animals decreased with increasing particle size. The intake for particles of 400–800 μm was about 10 times lower than that for fine particles sized 0–100 μm. It was found that the excretion rate of radioactive particles from the animal body also depends on particle size. The deposition of radioactive particles on the fundal surface of the wall of the ventral rumen sac and reticulum, as well as the long-term retention of radioactive particles of all sizes in the abomasum was noted. This can result in substantial damage in the GIT system, in particular, in these parts of the cattle digestive tract the focal ulcerative lesions of the mucous membrane can be formed by « hot » radioactive particles.

Size distribution of ambient and radioactive aerosols formed by the short-lived radon progeny

Abstract The survey of ambient airborne particle size distribution is important when the deposition of radioactive particles is considered in the human lung and the assessment of radiation hazard in occupational exposures or contaminated environments. CLOR (the Central Laboratory for Radiological Protection) in cooperation with CMI (the Central Mining Institute) performed simultaneous measurements of the activity size distribution of radon progeny and ambient aerosols using different types of aerosols. Measurements were performed in a radon chamber with a volume of 17 m3, where radon was generated by a radium-226 open source, and ambient aerosols by an oil candle, vax candle, and incense sticks. Such measurements were also made in an aerosol depleted atmosphere after cleaning the chamber air by means of a high-efficiency pump and filters. The size distribution of radioactive aerosols containing radon progeny was measured by RPPSS (Radon Progeny Particle Size Spectrometer) with the measuring size ranging from 0.6 nm to approximately 2500 nm. The key parts of this device are the impaction plates and diffusion screen batteries, which collect aerosols of different sizes, and semiconductor alpha detectors which detect the activity of the collected particles. The SMPS (Scanning Mobility Particle Sizer Spectrometer) and APS (Aerodynamic Particle Sizer) were applied to evaluate the size distribution of all aerosols with sizes from approximately 3 nm to 20 μm. Based on the results obtained by these spectrometers, the activity size distributions and related dose conversion factors (DCF) were evaluated both for the exposed workers and the general population.

Species removal from aqueous radioactive waste by deep-bed filtration

Performances of aqueous suspension treatment by deep-bed sand filtration were experimentally studied and simulated. A semiempirical deterministic model and a stochastic model were used to predict the removal of clay particles (20 μm) from diluted suspensions. Model parameters, which were fitted based on experimental data, were linked by multiple linear correlations to the process factors, i.e., sand grain size (0.5 and 0.8 mm), bed depth (0.2 and 0.4 m), clay concentration in the feed suspension (1 and 2 kgp/m3), suspension superficial velocity (0.015 and 0.020 m/s), and operating temperature (25 and 45 °C). These relationships were used to predict the bed radioactivity determined by the deposition of radioactive suspended particles (>50 nm) from low and medium level aqueous radioactive waste. A deterministic model based on mass balance, kinetic, and interface equilibrium equations was developed to predict the multicomponent sorption of 60Co, 137Cs, 241Am, and 3H radionuclides (0.1–0.3 nm). A removal of 98.7% of radioactive particles was attained by filtering a radioactive wastewater volume of 10 m3 (0.5 mm sand grain size, 0.3 m bed depth, 0.223 kgp/m3 suspended solid concentration in the feed suspension, 0.003 m/s suspension superficial velocity, and 25 °C operating temperature). Predicted results revealed that the bed radioactivity determined by the sorption of radionuclides (0.01 kBq/kgb) was significantly lower than the bed radioactivities caused by the deposition of radioactive particles (0.5–1.8 kBq/kgb).

Effect of Uncertainty in Nasal Airway Deposition of Radioactive Particles on Effective Dose

In the current ICRP human respiratory tract (RT) model (ICRP Publication 66), the deposition of particles in various regions of the RT during natural breathing is modelled by considering the RT as a series of filters, resulting in deposition probabilities for distal portions of the RT being dependent on those of the proximal segments. Thus, uncertainties in regional deposition in proximal segments of the RT are reflected or propagated in uncertainties in deposition in the distal segments of the lung. Experimental data on aerosol particle deposition have demonstrated significant variability in nasal airway (NA) deposition for different individuals studied. This report summarises the impact of introducing variability in NA deposition efficiency on the calculation of effective doses using the ICRP 66 model for selected radionuclides. The computer software LUDEP, modified for this purpose, was used to customise deposition patterns, and effective doses were calculated for several radionuclides ( 111 In, 106 Ru, 60 Co, 210 Po, 238 U and 239 Pu) chosen to represent isotopes with various decay schemes and half-lives. The results indicated significant but particle-size-specific effects of assumed NA deposition efficiencies on the calculated effective doses, which varied typically by factors of five to six. The majority of the variability was associated with direct effects on deposition patterns, but in some cases, alterations of radiation dose distribution within the various target organs also contributed to the variability. These results provide a basis for evaluating uncertainties due to inter-individual differences in deposition patterns for radiation protection and risk analysis.

On some properties of 222Rn short-lived decay products in air.

Simultaneous measurements were made of such properties as the fraction of charged and uncharged atoms, the balance of radioactive equilibrium between 222Rn and its daughters, and the concentration of aerosol particles and their mean radii in tunnel air. It became clear that the behavior of 222Rn decay products in tunnel air could be expressed well by equations based on a simple model, taking the following into account: the attachment of free atoms to aerosol particles, the deposition of radioactive particles on the tunnel wall, emission of alpha recoils from aerosol particles and the surface of the tunnel wall, and radioactive decay. In addition, the effective attachment coefficient of an observed RaA-atom was found to agree well with that calculated. The results obtained should facilitate in the future estimation of the relation between 222Rn daughters and the lung dose to the population.

LUNG MUCOCILIARY FUNCTION IN MAN: INTERDEPENDENCE OF BRONCHIAL AND TRACHEAL MUCUS TRANSPORT VELOCITIES WITH LUNG CLEARANCE IN BRONCHIAL ASTHMA AND HEALTHY SUBJECTS

Abstract Mucociliary function at various generations of the tracheo-bronchial tree was studied in man after inhalation and deposition of radioactive particles by gamma camera imaging. Quantitative values for linear velocities of mucus movement in trachea and large bronchi could be compared with the clearance rates from the whole lung. Mucus transport velocity in normal subjects averaged 5.5 mm min -1 for the trachea and 2.4 mm min -1 for main bronchi, and these velocities were associated with average lung clearance rates of 0.51 % min -1 for particles deposited on the ciliated airways. Only two of six bronchial asthma patients had measurable large airway velocities; the remainder exhibited mucus stasis in hilar regions with failure of transport through major bronchi and trachea, which correlated with lung clearance of only 0.26% min -1 . Beta-adrenergic aerosols enhanced mucociliary function in the normal subjects by increasing both central airway mucus transport (bronchial and tracheal velocities were raised 156 and 37% respectively) and lung clearance (by at least 50%). In the patients, beta-adrenergic aerosol increased mucus transport velocities to 2.5 and 3.7 mm min -1 for the main bronchi and trachea, respectively, and lung clearance rate to 140% over control rate. The marked delay in mucus transport in bronchial asthma occurred despite central particle deposition, almost wholly on the ciliated airway, which should have produced rapid lung clearance of particles. These data indicate that the ratio of tracheal to bronchial mucus transport velocities is equal to 2.7 in the normal lung; that tracheal velocities are normally close to maximum stimulated by beta- adrenergic agonists; that large bronchi have velocities only 40% of maximum. Bronchial asthma patients combine depression of mucus transport in peripheral, bronchial and tracheal airways, and all transport values are susceptible to marked increases with beta-adrenergic agent.

Tumours in mice after pulmonary deposition of radioactive particles.

SummaryThe intratracheal administration to BAF1 or CAF1 mice of plutonium and ruthenium particles suspended in Tween-80 or Pluronics caused an increased incidence of pulmonary adenomas compared with controls at levels of 0·1 μc 239PuO2 and 3·0 µc 106RuO2. Decreased incidence of adenomas was obtained at 0·16 µc 239PuO2 and 24·0 µc 106RuO2. Intravenous administration of similar particles caused an increased incidence at a level of 0·16 µc 239Pu(OH)4 and a decrease at 0·37 µc 239PuO2. Certain inconsistencies in the incidence values were noted.Histological lesions resulting from deposition of plutonium particles included fibrosis with bronchiolar proliferation and squamous metaplasia. Ruthenium particles caused the presence of numerous bizarre cells in fibrotic lesions. Plutonium particles were considered responsible for the development of two squamous-cell carcinomas and a bronchiolar carcinoma. Two bronchiolar carcinomas occurred in ruthenium-treated animals.