The dispersion of radon from tailings piles was studies on a specific site, by acquiring experimental data on the sources of radon and the observed air concentrations, trying to describe the dispersion of radon by different models and comparing the measured and predicted data. The selected test site situated at Lengenfeld in Saxony was composed of two main tailings piles backed against a natural hill, covered with a 0.5 m layer of soil and partially planted with small trees (epiceas) of about 3 m high, and also another zone in the bottom of the site where some tailings had been accidentally spilled away due to the rupture of the earthen dike of a settling pond. The geographical distribution of the radon source strength was measured on this site during one week, and further on assumed, for modelling purpose, to be in a first approximation constant throughout the year. The meteorological conditions of wind speed and wind direction were derived from previous measurements made on the site and estimated also from regional data. Long-term (annual) concentrations of radon in air were obtained from systematic measurements made with track detectors placed at fixed points on and around the site.
Characteristics of radon progeny above or nearby a waste pile
Initial investigations were made at the Crossen waste-rock pile (Saxony) in short-term experiments and long-term experiments. The short-term experiments consisted of sampling the radon and its progeny during 5-min periods, measuring the radon by an ionisation chamber and the radon daughters by the Thomas' method. It was shown that the activity concentrations of the radon daughters were much lower than the radon concentrations and that the equilibrium factor was around 0.1 under unstable weather and 0.2 under stable weather conditions. The long-term experiments were made by measuring the on-pile equilibrium factor over periods of one-month duration with the Megarad 04 device. Average values of 0.14, 0.11 and 0.06 were found in September, October and December respectively. These values are to be compared with the value of 0.7 usually found as a background value for the undisturbed terrestrial environment.
The uranium, radium and lead aquatic pathway was studied for an industrial dry settling pond situated at Lengenfeld (Saxony).
Sampling wells were drilled at different points on the pond. Determinations have been made of the hydraulic conductivity, grain size distribution and pore water composition at different levels. On another hand, uranium-238, radon-226 and lead-210 and their distribution between the solid phase and the pore waters have also been determined. All these measured data are to be used to run the geochemical and hydraulic models PHREEQE and NAMMU.
Pore waters from RKS1 samples have been analyzed for major and minor elements. The solid phases of the samples have been submitted to chemical and mineralogical analyses to determine their composition. The surface-layer cover is characterized by the predominance of alkaline-earth carbonate and sulfate, a neutral pH and weakly reducing conditions. The tailings layer is characterized by a noticeable proportion of sodium carbonate and an alkaline pH (approximately 10.2) that probably result from an alkaline treatment of the ore, and shows a greenish colour which is indicative of strongly reducing conditions. The underlying soil consists of river sediments, it has a low alkaline pH (approximately 8.3) and is probably in reducing conditions.
Areas that have been affected by U-extraction and processing are a source of natural radionuclides and contribute to the radiation dose received by the population living in the vicinity. Three research organisms, IPSN France, Bfs and GRS Germany, propose a cooperative study of two sites situated respectively in two different geochemical environments of France and Germany. The broad objective is to characterize these sites, acquire a knowledge of the on-going migration processes, determine parameters to drive, validate and improve predictive models. GRS Will develop models that describe the atmospheric and terrestrial pathways; Bfs and IPSN will concentrate on acquiring data in the field and taking samples for analysis. The three teams will cooperate in comparing techniques and results, validating and improving the models,determining the kind and extension of measurements to evaluate other sites, and finally producing an initial methodology and data base to support the selection of appropriate remedial actions.
Funding SchemeCSC - Cost-sharing contracts