[en] An important feature in radiological safety studies of sites is the knowledge of water movements in the unsaturated layer surmounting aquifer; this zone of aerated soil can be effective as a protection against aquifer contamination. Utilizing a neutron-moisture meter, a method was developed permitting to build graphically the hydric states of soil and the moistened volume evolution with time in the particular case of a limited feeding surface. It is also possible to measure moisture gradients, drying kinetics, the retention capacity of soil and the gravific water content achieved by a given water head. The initial hydric state has an effect only upon the infiltration rate and neither upon the moistened front position nor upon the volume of moistened soil; consequently, the storable water amount in soil can be calculated. When water feeding has been stopped, the volume of moistened soil increases to an equilibrium state restricted by the moistened front and all the other water movements occur exclusively inside this volume. Consequently in case of radioactive waste disposal, the ionic pollution will be confined inside a measurable volume, the moistened front being the maximum limits of this volume. Part 2. Following up the report on water movements in non-saturated s o i l s after reject on a limited space - CEA R 3635 (1) - the radioactive ions movements in these soils are studied in using an anion and a cation of reference: iodine 131 and strontium 85. The experimental method is founded on the simultaneous measurements of moisture and radioactivity fronts by means of a neutrons moisture meter and an specially conceived radioactivity probe. It has so been possible to measure: the relative velocities of moisture and radioactivity fronts; the contaminated soil volume inside the moistened oil volume; the concentration gradients; the contamination changes upon watering; the effect of chemical composition of water upon this ions movements and the effect of soil moisture upon the counting rate of radioactivity. This method which have allowed to get various results about ¹³¹I and ⁸⁵Sr can be generalized to other radioisotopes and other soils. They are applicable to radiological safety of sites studies : Testing storage plants, estimate of accidents hazards and protection of subterranean waters. (author)

No abstract available

[en] Published in summary form only

No abstract available

[en] The capillary barrier technique, by which one can create dry structures in porous media relying simply on the differences of particle size distribution between two media, has been demonstrated by laboratory experiments on reduced-scale models. In order to test the applicability of this phenomenon to practical waste storage, an experimental trench was excavated in fine soil, filled two-thirds with gravel and then covered with argillaceous sand of fine texture which formed a dome above the soil surface. Moisture transport was observed by measuring the evolution of water profiles with a neutron moisture gauge and by noting the movement of radioactive tracers. Static measurements were also performed with a strainer pipe going down to the bottom of the trench. The influence of atmospheric precipitation was recorded during several seasonal cycles; experiments were also carried out with intensive water spraying on the trench surface. After five years of regular observation, in spite of the intensive irrigation conditions no apreciable moisture transport was observed across the interface of the fine medium towards the coarse medium, which indeed remained a dry structure. Applied with certain precautions, this simple, sturdy and inexpensive method can considerably improve the safety of underground repositories for low- or medium-level wastes. (author)

No abstract available

No abstract available

[en] There is a basic difference between the coefficients of retention according to the texture of the sorbent medium. In the case of transfers in open fissures in compact rocks, use must be made of a surface retention coefficient; if the rock manifests a certain matrical permeability, the impregnation effect should be taken into account. An experimental method is put forward for measuring retention coefficients in the case of surface elements in rock fissures. The experimental rig, which is simple enough to be reproduced fairly frequently, permits comparative measurement of the retention of various isotopes by different rock types, and also makes it possible to measure the reversibility of sorption effects quite easily. (author)

[en] Several methods of investigation of iodine retention and migration in the soil are compared: Laboratory processes (batch and column methods), intermediate processes (lysimetry) and direct field experiments. Iodine is generally used in iodide form, but may be oxidized. It behaves as a water tracer in laboratory experiments because of very low retention by minerals. In natural soils iodine behavior is quite different, as organic material, plant litter or certain oxidation processes can delay migration or leaching. Iodine behavior is then compared in various types of soils, minerals and ores to determine a geochemical barrier liable to be used to trap radioactive iodine in a waste repository. Some twenty typical materials were investigated including aluminosilicates and clays, as well as iron, lead, aluminium and copper ores. Only certain copper ores appear suitable. Among them, chalcopyrite has the best sorption properties. It is examined for use as a geochemical barrier for radioactive iodine by addition in various concentrations in other materials. (orig.)

[en] We have studied the retention of actinide elements (Np, Pu, Am) and of Cs in the sediments of the ocean deeps around Cap-Vert. Plutonium: retention increases with temperatures of 4 to 30⁰C, then stays constant from 30 to 80⁰C. Desorption is slow. Americium: absorption is very strong at any temperature. Measurements of a wide variety of sediments show that retention is not affected by facies (including carbonated sediments). Neptunium: retention is more or less constant between 4 and 15⁰C, and distinctly higher at 30-50⁰C. It is reversible. Caesium: absorption decreases slightly from 4 to 30⁰C, but increases rapidly at 50 to 80⁰C. At the lowest temperatures it is reversible, but it appears to be irreversible at 50⁰. Cs absorption is subject to ponderal concentration. With equal amounts of activity, retention of Cs-135 is weaker than that of Cs-137: likewise the addition of the stable isotope causes in the amounts of Kd in Cs-137. Finally, this paper presents preliminary results showing the natural metallic element content of the sediments