Objetivo
The objectives are to improve, where necessary, the models and parameterizations used in estimating the intensity and spatial distribution of deposited activity, and the total health and economic impact of such deposits in assessments of the consequences of accidental releases of radioactivity. To this end it is hoped to attain a better understanding of:
the influence of various weather conditions on deposition, particularly weather conditions which can lead to high deposition fluxes such as fog, snow or intense rain;
resuspension of deposited 137Cs activity;
the weathering of deposits in urban and rural environments and its impact on long term external exposure;
the ultimate fate and dosimetric impact of radionuclides carried by urban runoff water;
the impact that a change in the method of representing the atmosphere's dispersion capabilities would have on the end points of consequence assessment.
An investigation has been carried out into the factors influencing the incorporation of radionuclides into fog particularly the competition between the released aerosol and the natural aerosol for the available fog water. 2 approximate approaches were developed which provide powerful insights into the dependence of the enhancement factor (enhancement in deposition produced by the released particles) on the characteristics of the released aerosol. It appears that the key parameters required to specify the deposition velocity appropraite in fog are the total mass concentration and the mass median aerodynamic diameter. Approximate estimates of the geometric standard deviation of the number distribution, the fraction (by volume) of soluble material and the dry particle density will usually suffice. The work indicates that it should be possible to make an adequately reliable estimate of the impact of fog in probabilistic consequence assessment despite the fact that detailed information on the released aerosol characteristics may be lacking.
A review has been carried out covering: urban drainage systems; radionuclide behaviour in the system; and radiological and economic implications. Some generalizations are possible. For example, combined systems are still common in Europe indicating that sewage treatment is a factor that has to enter into an assessment of the ultimate effect of radioactivity in the drains. Generally, information on the absolute amounts of water entering the system will be required to assess the publichealth impact of contaminated runoff water entering the drains. Empirical information on the partitioning of radionuclides between the solid and liquid phases in the sewage system is sparse. Little is known of the effect of chemical treatment of sewage on radionuclide behaviour.
Contamination levels of caesium-134 and caesium-137 have been measured in Sweden and Denmark to follow the influence of natural decontamination and weathering processes in urban areas. From a comparison with measurements made 2 years previously, it can be seen that there has been little or no decrease in the caesium level on grassed surfaces. On paved surfaces, the levels had decreased by 53% to 70%. A model, TACTUC, for describing the time dependence of the contamination is under development and the contamination levels on different urban structures are simulated.
The depth profile of caesium in asphalt roads has been measured at 3 different locations. It was found that 80% to 90% of the total caesium is still in the uppermost 2 mm of the asphalt layer.
Rain collectors for measuring the resuspended material in rain have been erected at 2 different heights and the measurements of the collected rainwater is in progress. The first measurement did not show any significant difference in the collection of resuspended material at the 2 heights but further measurements have to be done in order to give a valid conclusion.
A tracer method for the measurement of washout of particles by rain and snow has been established and the first measurements made. These experiments showed that, in the considered size range (0.6 to 4 um), there was only a weak dependence of the washout process on the particle size while a significant difference was observed depending on the precipitation type (rain or snow) or the precipitation intensity. The direct measurement of the wet deposition of atmospheric aerosol was also started. It was found that the scavenging efficiency of snow is up to one order of magnitude higher than that of rain and that the dependence on particle size is similar to that of rain (ie small aerosol particles (less than 0.5 um) and large aerosol particles (less than 1.5 um) are scavenged most effectively.
The evaluation of the photon spectra recorded at 50 locations in southern Bavaria showed that the site specific differences of the attenuation of the gamma radiation from deposited caesium increases with time after deposition.
The resuspension of deposited caesium-137 was measured in Goiania, Brazil where an accident with a medical caesium source led to highly localized contamination. Preliminary results on air concentrations indicate a rather local source of resuspension and negligible differences in air concentrations between 1 m and 2 m above the ground. Apparently over 90% of airborne activity is attached to aerosols larger than the cut point of the EPA type air sampler. The street dust results show a rather minute dispersion after 3 years of the initial urban contamination.
Work programme
Below, the work programme is given separately where possible for the first and second years. Not all aspects mentioned below could be fully explored in the two years, and the work could be carried forward into subsequent years if the Programme continues.
The influence of weather condition on the intensity and pattern of deposition
In the first year, SRD will investigate the factors influencing the incorporation of radionuclides into fog. The first stage would be an appraisal of recent developments in reactor accident source-term research, particularly regarding the solubility characteristics of released particles, in order to address the question of the competition with the natural aerosol for the available fog water. It will also assess the feasibility of utilizing routinely recorded meteorological data to provide information on the presence of fog and an indication of its intensity and type.
SRD would also commence an assessment of the impact of changing the representation of the dispersive capability of atmospheric states.
In the second year (and beyond if appropriate) SRD will consider the design of algorithms for including foggy conditions in consequence-assessment codes. It would also continue the model uncertainty-sensitivity analysis commenced in the first year.
Weathering and runoff of 137Cs in urban and rural environments
In the first year, GSF will carry out in situ gamma ray spectrometry at about 55 locations in urban, suburban and rural environments in Bavaria which have been continuously investigated since the reactor accident at Chernobyl.
Resuspension of deposited 137Cs activity
In the first year, Risoe will collect data on the content of resuspended 137Cs in rainwater and also on deposition levels of 137Cs with a view to correlating the two sets of data. Where possible, the corresponding air concentration will also be measured. In addition, rain will be collected at an elevated location in order to test whether the surprisingly high concentrations of resuspended 137Cs found in rainwater collected at ground level may be caused by splash from the ground. In the second year, the data collected in the first year will be processed.
Ultimate fate of deposited radionuclides
In the first year, SRD will identify the dominant mechanisms determining the patterns of retention and redistribution of radionuclides throughout the system of urban drainage, storm runoff and water treatment plants. This work would commence with a review of pertinent information, including that available from nonnuclear contexts.
In the second year (and beyond if appropriate) SRD will seek to quantify the radiological impact of runoff into the urban drainage system in terms of its contribution to the endpoints of consequence assessment.
Ámbito científico (EuroSciVoc)
CORDIS clasifica los proyectos con EuroSciVoc, una taxonomía plurilingüe de ámbitos científicos, mediante un proceso semiautomático basado en técnicas de procesamiento del lenguaje natural. Véas: El vocabulario científico europeo..
CORDIS clasifica los proyectos con EuroSciVoc, una taxonomía plurilingüe de ámbitos científicos, mediante un proceso semiautomático basado en técnicas de procesamiento del lenguaje natural. Véas: El vocabulario científico europeo..
- ciencias naturales ciencias químicas química nuclear química de la radiación
- ciencias naturales ciencias físicas física teórica física de partículas fotones
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Régimen de financiación
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Régimen de financiación (o «Tipo de acción») dentro de un programa con características comunes. Especifica: el alcance de lo que se financia; el porcentaje de reembolso; los criterios específicos de evaluación para optar a la financiación; y el uso de formas simplificadas de costes como los importes a tanto alzado.
Coordinador
WA3 4NE Warrington
Reino Unido
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