Status report on standard-setting work in the area of environmental radioactivity measurement.

Environmental assessment studies are regularly commissioned to study the impact of radioactive substances on the environment and the public, in response to concern about the presence of such substances. The credibility of such studies relies on the quality and reliability of radionuclide analysis as well as the sample representativity of the radiological situation. The recent expansion from national stakeholders to those involving other states requires that activity measured in effluents or environmental samples in a country are reliable and reproducible so as to be accepted by all states potentially concerned by regional contamination. The standard-setting approach, based on consensus, seemed to lend itself to a settlement of technical aspects of potential dispute. This document describes standardization organizations, French and international, the standards published, as well as standardization work under way on the measurement of radionuclides found in environmental matrices.

Study of a predictive methodology for quantification and mapping of the radon-222 exhalation rate.

We propose a new methodology for predicting areas with a strong potential for radon (222Rn) exhalation at the soil surface. This methodology is based on the Rn exhalation rate quantification, starting from a precise characterisation of the main local geological and pedological parameters that control the radon source and its transport to the soil/atmosphere interface. It combines a cross mapping analysis of these parameters into a geographic information system with a model of the Rn vertical transport by diffusion in the soil. The rock and soil chemical and physical properties define the entry parameters of this code (named TRACHGEO) which calculates the radon flux density at the surface. This methodology is validated from in situ measurements of radon levels at the soil/atmosphere interface and in dwellings. We apply this approach to an area located in western France and characterised by a basement displaying a heterogeneous radon source potential, as previously demonstrated by lelsch et al. (J. Environ. Radioactivity 53(1) (2001) 75). The new results obtained show that spatial heterogeneity of pedological characteristics in addition to basement geochemistry--must be taken into account to improve the mapping resolution. The TRACHGEO forecasts explain the Rn exhalation variability on a larger scale and in general correlate well with in situ observations. Moreover, the radon-prone sectors identified by this approach generally correspond to the location of the dwellings showing the highest radon concentrations.

An automatic device for measuring the effect of meteorological factors on radon-222 flux from soils in the long-term.

An automatic method for measuring the radon flux at soil surfaces is described. The proposed experimental design minimises the disturbance induced by the accumulator technique widely used to measure radon exhalation from the ground. By exposing the ground surface to the normal weather conditions between two consecutive measurements, this method can be used to study, in the long term, the effects of meteorological factors on the radon flux density at the soil-atmosphere interface.

Radon exhalation from uranium mill tailings: experimental validation of a 1-D model.

TRACI, a model based on the physical mechanisms governing the migration of radon in unsaturated soils, has been developed to evaluate the radon flux density at the surface of uranium mill tailings. To check the validity of the TRACI model and the effectiveness of cover layers, an in situ study was launched in 1997 with the French uranium mining company, COGEMA. The study consisted of continuous measurements of moisture content, suction, radon concentration at various depths inside a UMT cover, and flux density at its surface. An initial analysis has shown that radon concentration and flux density, as calculated with a steady-state diffusion model using monthly averaged moisture contents, are in good agreement with measured monthly averaged concentrations and flux densities.

Radon (222Rn) level variations on a regional scale: influence of the basement trace element (U, Th) geochemistry on radon exhalation rates.

The approach proposed in this study provides insight into the influence of the basement geochemistry on the spatial distribution of radon (222Rn) levels both at the soil/atmosphere interface and in the atmosphere. We combine different types of in situ radon measurements and a geochemical classification of the lithologies, based on 1/50,000 geological maps, and on their trace element (U, Th) contents. The advantages of this approach are validated by a survey of a stable basement area of Hercynian age, located in South Brittany (western France) and characterized by metamorphic rocks and granitoids displaying a wide range of uranium contents. The radon source-term of the lithologies, their uranium content, is most likely to be the primary parameter which controls the radon concentrations in the outdoor environment. Indeed, the highest radon levels (> or = 100 Bq m-3 in the atmosphere, > or = 100 mBq m-2 s-1 at the surface of the soil) are mostly observed on lithologies whose mean uranium content can exceed 8 ppm and which correspond to peraluminous leucogranites or metagranitoids derived from uraniferous granitoids.

Study of 222Rn permeation through polymer membranes II: calibration curves of a new device equipped with a polyethylene membrane, for continuous measurement of 222Rn in water-saturated soils.

The permeation of 222Rn through plastic membranes has been studied in order to improve a solid-state measuring device BARASOL and to use it in water-saturated soils. Preliminary results show that polyethylene is the most efficient membrane (sufficiently permeable to radon and impermeable to water). In the present study, we have adapted polyethylene membranes to the BARASOL probe and tested them, in this configuration, with a special experimental set-up. We have shown that it is possible to measure radon concentrations in water of about 1 Bq L(-1) with this probe.

Study of atmospheric pollution in an urban zone deprived of measurement systems, for purposes of legislation application to the city of Tunis.

In order to legislate on and provide against the atmospheric pollution specific to a country in a region deprived of measurement systems, it is first necessary to examine the following points: - location of chief pollution sources, - emission characteristics of the main source, - effects of the source on the environment, - predictable effects of applied legislation. In the city of Tunis for example the road traffic was identified as the major source of pollution. Ways to cut down the pollution level are proposed on the basis of different short-term measurements. Calculation shows that if rules similar to those laid down in France were applied and the traffic flow organised the levels of certain pollutants (CO, NoX) would be substantially reduced.