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EVALUATION OF THE POPULATION EXPOSURE TO RADON IN THE VICINIY OF URANIUM MINING FACILITIES

Objective

The objectives are:
to carry out surveys of radon concentrations in homes in those countries where insufficient data is available;
to develop and test techniques for identifying areas with a potential for high radon concentrations in homes, both on a large scale and for individual building sites;
to improve the understanding of, and develop mathematical models of, the movement of radon from the ground to subfloor spaces and into buildings;
to develop and test countermeasures against radon in homes using laboratory and field studies.
The indoor radon survey for the determination of radon concentrations in Portuguese dwellings, was extended. A initial selection of houses to be surveyed in the vicinity of the uranium tailings (at Urgeirica) and of the old radium salts factory (at Barracao), was made. Due to some high values found in dwellings from these 2 zones, this survey was pursued. The programme was also enlarged to some towns and villages from the granitic region of Beira Alta, and in 1989 to the whole granitic region.

Simultaneously some measurements started being performed in other regions from the country, in order to contribute to the European Atlas on natural radiation.

Outdoor radon concentrations were also measured, in order to calculate their contribution to radon inhalation by the critical groups. Mathematical simulation of outdoor radon concentrations were developed, and meteorological data collected.

Concerning indoor radon concentrations, the results clearly show 3 different levels of activity, accordingly to the studied regions the highest reading was due to the influence of wastes from the old radium salts factory (907 Bq m{-3}) and from the uranium tailings (755 Bq m{-3}). The granitic region activity level was 108 Bq m{-3} and the nongranitic region gave readings of 41 Bq m{-3}.

Comparing the geometric means of indoor radon concentration in the granitic and nongranitic regions a ration of about 3 can be observed.
The corresponding doses to the population due to radon inhalation would be on the order of 40, 5, and 2 mSva{-1}, for each of these regions, respectively.

In Portugal, the granitic regions are situated in a climatic zone colder than most of the nongranitic ones. So, the high values found in those regions could be explained by the geological composition of the soils, probably enhanced by a poor ventilation of the dwellings. Observing all the individual values, it was verified that 4% of dwellings have indoor radon concentration below 20 Bq m{-3} and ap proximately 10% present levels higher than 400 Bq m{-3}. The most frequent values are situated between 50 and 150 Bq m{-3} (about 40%}.

The obtained results seem to confirm that the main cause for the elevated indoor radon concentrations in houses would be the influx of radon through the soil beneath the houses.

Concerning the outdoor radon concentrations and the gamma dose measurements, there is not a clear agreement between both values. These measurements should be repeated and the corresponding meteorological data should obtained in order to get a better understanding of the situation.
The main objective of implementing a mathematical model for predicting the atmospheric dispersion of radon has been accomplished. However, it was not yet possible to obtain site specific meteorological data to run the model in realistic conditions, due to difficulties in installing the anemograph at Urgeirica.

The national indoor radon survey was pursued with measurements being taken in about 3560 houses in all 276 countries. The observed concentrations range from 6 Bq m{-3} to 2700 Bq m{-3}. The arithmetic mean values obtained in the different countries were sent to the National Radiological Protection Board (NRPB) in order to contribute to the European atlas of natural radiation. It was found that 58.5% of the values were below 50 Bq m{-3} but 9.4% were above 200 Bq m{-3}.

Measurements were made in some selected houses to evaluate the equilibrium factor for radon and its decay products. For this purpose, both passive and active dosemeters were used together. Only a few results have been obtained so far, ranging from 0.41 to 0.72.

Measurements were taken in the vicinity of the uranium mining facilities to study the horizontal and vertical dispersion of the radon emitted from the tailings. Dosemeters were placed in a grid of 100 m by 100 m within an area of 500 m by 500 m. Some dosemeters were exposed at heights from 2 m to 12 m. A mean radon concentration of 71 Bq m{-3} was found.
LNETI (P), University of Cantabria (E), University of Athens (GR) and NSCR Demokritos (GR) will carry out surveys of the exposure of the population to radon in Portugal, Spain and Greece. These will be carried out using passive etched track detectors and active measurement techniques. Additional data will be collected on the radon decay product equilibrium factors and on the origins and characteristics of the radon sources. The average radon concentrations in homes will be calculated, and the variations in concentrations mapped.

BGS (UK) and NRPB (UK) will identify appropriate geological and radiological parameters for radon potential mapping. Existing data will be evaluated, and programmes of collection of relevant data including radionuclide contents of rocks and soils will be started in defined areas. This information will be used to construct maps of radon potential, which will be compared with data on radon concentrations in homes, both from earlier surveys and from new surveys designed to test the validity of the maps. .SP 1 KVI (NL), CSTC (BE), TNO (NL) Risoe (DK) and SSI (S) have under development mathematical models of radon movement and availability in the soil, movement into buildings through subfloor spaces where present, and subsequent dilution and dispersion. Different models emphasise different parts of this process. These laboratories will meet to exchange information on their models and to draw up a programme of model comparison. The results from the models will also be compared as closely as possible with measurements and will be used to identify the most important parameters for measurement in assessing radon problems in homes.

KVI (NL), the Technical University of Denmark and Risoe (DK) will study soil factors influencing radon availability to buildings using laboratory and field studies. These will include the radon exhalation rate of materials, the influence of porosity, permeability and groundwater on radon movement, and the development of improved instrumentation for characterizing soils on site. The results of this work will be used as input for the mathematical models described above.

WTCB (BE) and TNO (NL) will carry out laboratory and site studies of constructional factors influencing the entry of radon into buildings from the ground. The insight gained will be used in the development and testing of remedial and preventive measures to avoid high levels. This will include the testing of the effectiveness and durability of barrier and diversion techniques for preventing the entry of soil gas.

In the UK, some existing buildings have had remedial measures installed and thousands of new buildings have been constructed using antiradon designs. NRPB will survey the radon levels in a representative sample of these buildings to determine the effectiveness and durability of different countermeasures in practice.

In view of the wide scope of these contracts, it has been found necessary to set up small working groups to coordinate the work on particular topics where there might otherwise be duplication of effort. These groups will exchange information and will meet as required. NRPB will attend the meetings of the groups. The Technical University of Denmark, KVI and the University of Cantabria will collaborate on the subject of soil permeability measurements. KVI, Risoe, CSTC and the Technical University of Denmark will collaborate on models of radon movement in soils and into homes. SSI, CSTC and TNO will collaborate on compartmental models of airborne radon movements within homes, also using data from earlier KVI studies. Within each group the first named laboratory will take the lead in arranging the collaboration, with assistance from NRPB as required.

Apart from cooperation on the specific topics mentioned, all the laboratories will maintain communication with each other and with laboratories in Europe and North America on topics of mutual interest.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

LABORATORIO NACIONAL DE ENGENHARIA E TECNOLOGIA INDUSTRIAL
Address
Dpsr - Azinhaga Dos Lameiros A Estrada Do Paco Do Luminar
1699 Lisboa
Portugal

Participants (2)

IPSN
UNIV. NOVA DE LISBOA