[en] The nine types of geological formations with uranium deposits (superficial, precambrian conglomerates, sandstones...) are reviewed. U ore deposits are generally the product of successive enrichments during the geological cycle. Two main mechanisms control U fractionation during the cycle: partial melting followed or not by fractional crystallization and redox reactions. Most of the U ore deposits were formed in relation with major geodynamic events. The most interesting deposits from an economical point of view are the Proterozoic unconformity related deposits which contain very large reserves at a much higher grade than in other deposits

[en] Uranium has a single civil use, fueling the nuclear power plants; hence its needs and consumption are fully governed by electricity generation nuclear programs which are presently slowed down. Past uranium production is by far not completely burnt. Hence, past stocks are partly a burden for present and future market in the form of excess inventories in the form of a huge potential of fissile materials contained in nuclear weapons and recycled fissile materials from spent fuel reprocessing. These resources combined with newly discovered ore-bodies have developed a long term security of supply feeling on the consumers side, reinforced by depressed prices. However, a fresh uranium production is needed to ensure and secure the nuclear power plants operations, which represents a problem considering the low market prices of uranium. 7 figs., 1 tab., 8 refs

[en] The development of reactors which, at the turn of the century, will replace the present units in France and in Europe, raises new questions in a new international environment. Whether of industrial nature, concerning safety or public acceptance, the questions are now addressed within an european approach, based upon a Franco-German kernel (European Pressurized Reactor), and organized around a ''European Utilities Requirements'' basis. Renewed public acceptance will be set up through enhancement of the safety of future reactor and the understanding of a need for rapid reactors

[en] The caesium 137 isotope is distributed in the atmosphere during nuclear explosions, and is absorbed in the upper horizons of the soil on reaching the ground. When it is incorporated in the fine fraction of the soil, caesium 137 measurement allows movements affecting cultivated lands (mass movements, runoff effects, wind action) and rate of soil degradation over half a century to be evaluated. Vegetal cover and techniques of soil utilization must be considered; this method has been tested on a watershed in the Parisian Basin. 5 figs., 26 refs

[en] Global Change focuses on the understanding and estimation of the environmental changes to be expected in the near future. Geology may be used to understand the future. Quaternary geology possesses a high time resolution that allows the identification and correlation of events on a decadal to century basis, sometimes even on a yearly to seasonal basis. The short-term climatic-eustatic changes seem primarily to be driven by the redistribution of energy and water masses within given budget frames. Present warming is not linked to any significant future change in sea level; at the most, 10-20 cm in a century. The first future Ice Age is to be expected in about 5000 years, with significance for long-term deposition of nuclear wastes. (author). 4 figs., 44 refs

[en] Several examples are presented showing the usefulness of isotope techniques for hydrological surveys: aquifer circulation (²H, ¹⁸0), pluviogenesis and evaporation rate measurements, recent and ancient underground water dating (³H, ¹⁴C and ¹³C, ³⁶Cl)

[en] Nearly two billions years ago, fission chain reactions set up spontaneously in small portions of a uranium deposit in Gabon, and were sustained for sufficiently long periods for the isotopic compositions of many elements to be deeply modified. These natural reactors were found remarkably preserved. Through neutronic analysis, the operating conditions were reconstituted: during reactions, heat release turned out in convection streams, which dissolved quartz and so eliminated large amounts of silica, densifying uranium and deeply modifying geometry and composition of the rocks; reactors were mainly controlled by temperature which modified water density. 3 figs., 1 tab., 5 refs

[en] Some phases of the cycles of certain radioelements the period of which is long enough to interfere with man, are described. The behaviour of radionuclides is closely linked with the concomitant presence of isotopes or stable analogues in secular equilibrium in the medium; sources (nuclear explosions, cosmic radiations, nuclear reactors, ...) and behaviour of carbon-14, technetium-99, iodine-129, neptunium-237 and plutonium-239 are briefly described

[en] Studies about hydrogen and fluorine incorporation in various materials used by the prehistoric man, bring to archaeological stratigraphies important information about chronology. Ion beams methods of analysis (such as AGLAE for the Louvre museum), provide depth resolution together with high detection sensitivity. They allow to pursue researches most often without sampling the artefacts. Some resonance nuclear reactions, such as produced by nitrogen 15 nucleus and protons, allow for measuring the concentration profile of fluorine and hydrogen present in the outer micrometer of the surface. Examples of the obsidian hydration and the fluorine penetration in flint or paleontological remains, show the interest of these methods to complement traditional methods of absolute dating. (author). 3 figs., 2 tabs., 34 refs

[en] An experimental procedure for in situ quantitative analysis of nitrogen in silicates with a nuclear microprobe using nuclear reactions is presented. The procedure uses the simultaneous detection of protons and alphas emitted from N nuclear reactions. A lower detection limit of 10 ppm, with an analyzed depth inferior to 20 micrometers, has been obtained. The nitrogen content measured in feldspar and muscovite crystals by the nuclear microprobe is perfectly consistent with quantitative nitrogen determinations by catharometry and semi-quantitative determinations by FT-IR microspectrometry. 4 figs., 3 tabs., 21 refs