La problématique de la radioactivité dans les objets patrimoniaux: identification, évaluation et gestion

Le présent travail traite de cette problématique délicate et bien souvent ignorée. Ce travail a été réalisé dans le but de fournir aux musées des protocoles de comportement afin de réagir au mieux à la présence de substances radioactives et d'éviter tout incident. Les quatre questions suivantes sont traitées : · Quels sont les objets radioactifs susceptibles d'être trouvés dans un musée et comment les identifier ? · Que dit la loi sur la possession et la gestion de ces objets ? Comment se situe le musée par rapport aux textes de réglementation ? · Comment évaluer la dangerosité de ces objets et comment les gérer ? · Y a-t-il des traitements possibles pour réduire le danger ?The present work deals with this delicate and often ignored problem. This work has been realized with the purpose of giving museums protocols of behaviour allowing for an ideal reaction in the presence of radioactive substances and to avoid any incident. The four following questions are treated: · What radioactive objects are potentially found in a museum and how can one identify them? · What does the law say about the possession and handling of those objects? What is the museum's position with respect to the law texts? · How can one evaluate the danger of these objects and how can one handle it? · Are there any treatments allowing for a reduction of the danger?Die vorliegende Arbeit befasst sich mit diesem sensiblen und oft ignorierten Thema. Diese Arbeit wurde durchgeführt, um den Museen Verhaltensprotokolle zu bieten, um im Vorhandensein von radioaktiven Stoffen am besten zu reagieren und um jene Zwischenfälle zu vermeiden. Die folgenden vier Fragen werden behandelt: · Welche sind die radioaktiven Elemente, die in einem Museum gefunden werden könnten und wie kann man sie identifizieren? · Wie läutet das Recht auf Eigentum und Management dieser Objekte? Wie funktioniert das Museum gegenüber der Gesetzestexten? · Wie kann man die Gefährlichkeit dieser Objekte abschätzen und wie soll man mit ihnen umgehen? · Gibt es Behandlungen zur Verfügung, um die Gefahr zu verringern

Les substances radioactives dans les objets patrimoniaux

Sans odeur, ni bruit, ni forme physique particulière, la présence de substances radioactives dans les objets de collection est difficilement détectable. La gestion de ce patrimoine particulier tant au niveau pratique que juridique est de ce fait délicate. La peur liée à leur nocivité et l’ignorance des solutions de gestion poussent souvent à mettre de côté ces objets alors qu’ils sont emblématiques du début du XXe siècle. Dans le but de mieux appréhender ce patrimoine, l'étude est articulée autour de trois axes principaux : l'identification des objets radioactifs, l'évaluation de leur dangerosité et la gestion de ces collections par des actions préventives ou curatives.Odourless, noiseless and without any specifically perceptible physical form, the presence of radioactive substances in patrimonial objects is not easily detectable. Therefore, the management of this particular patrimony appears problematic, on its practical as well as legal aspects. The fear of their noxiousness and the lack of knowledge about management solutions often leads to the exclusion of these objects, although they are highly emblematic of the 20th century. For a better comprehension of this patrimony, this study is articulated around three main themes: the identification of radioactive objects, the estimation of the hazard and the management of these collections using preventive or curative actions

pH-dependent control of feldspar dissolution rate by altered surface layers

Relevant modeling of mass and energy fluxes involved in pedogenesis, sequestration of atmospheric CO2 or geochemical cycling of elements partly relies on kinetic rate laws of mineral dissolution obtained in the laboratory. Deriving an accurate and unified description of mineral dissolution has therefore become a prerequisite of crucial importance. However, the impact of amorphous silica-rich surface layers on the dissolution kinetics of silicate minerals remains poorly understood, and ignored in most reactive transport codes. In the present study, the dissolution of oriented cleavage surfaces and powders of labradorite feldspar was investigated as a function of pH and time at 80 °C in batch reactors. Electron microscopy observations confirmed the formation of silica-rich surface layers on all samples. At pH = 1.5, the dissolution rate of labradorite remained constant over time. In contrast, at pH = 3, both the dissolution rates at the external layer/solution interface and the internal layer/mineral interface dramatically decreased over time. The dissolution rate at the external interface was hardly measurable after 4 weeks of reaction, and decreased by an order of magnitude at the internal interface. In another set of experiments conducted in aqueous silica-rich solutions, the stabilization of silica-rich surface layers controlled the dissolution rate of labradorite at pH = 3. The reduction of labradorite dissolution rate may result from a gradual modification of the textural properties of the amorphous surface layer at the fluid/mineral interface. The passivation of the main cleavage of labradorite feldspar was consistent with that observed on powders. Overall, our results demonstrate that the nature of the fluid/mineral interface to be considered in the rate limiting step of the process, as well as the properties of the interfacial layer (i.e. its chemical composition, structure and texture) to be taken into account for an accurate determination of the dissolution kinetics may depend on several parameters, such as pH or time. The dramatic impact of the stabilization of surface layers with increasing pH implies that the formation and the role of surface layers on dissolving feldspar minerals should be accounted for in the future

Influence of etch pit development on the surface area and dissolution kinetics of the orthoclase (001) surface

The (001) orthoclase surface was dissolved at 180 °C and at far from equilibrium conditions with an alkaline solution (pH180 °C = 9) in a titanium open flow reactor. Vertical scanning interferometer (VSI) and atomic force microscope (AFM) surface monitoring were periodically used during the reaction process in order to quantify the surface topography evolution. The dissolution of the (001) orthoclase face occurs with the formation of diamond shape etch pits. Diamond pit diagonals are parallel to the [100] and [010] axes, and the pit walls are parallel to (6 5 6), 65¯6, (6¯511) and 6¯5¯11 planes. The etch pit size and global surface retreat of the (001) surface were found to increase linearly with time. Based on statistical treatments of etch pit development monitoring by AFM, we designed a numerical model aimed at reproducing and quantifying the total surface evolution. Numerical results show that the stabilization of etch pits doubles the calculated dissolution rate, partly due to the intrinsically higher reactivity of pit walls, consistent with a dissolution process in line with the periodic bond chain (PBC) theory. In addition, normalizing the dissolution rate by the initial surface area of the (001) orthoclase surface induces a 20% overestimation of the calculated dissolution rate, while the total surface area of the dissolving face reaches a steady state after a few days of reaction. Additional simulations conducted to assess the impact of defect parameters revealed a weak dependence of the dissolution rate on dislocation density, consistent with previous experimental observations. Overall, the combined effect of the various defect parameters does not affect the dissolution rate by more than an order of magnitude, and probably contributes to a moderate extent to the dispersion of mineral dissolution rate data reported in the literature

Does crystallographic anisotropy prevent the conventional treatment of aqueous mineral reactivity? A case study based on K-feldspar dissolution kinetics

International audienceWhich conceptual framework should be preferred to develop mineral dissolution rate laws, and how the aqueous mineral reactivity should be measured? For over 30 years, the classical strategy to model solid dissolution over large space and time scales has relied on so-called kinetic rate laws derived from powder dissolution experiments. In the present study, we provide detailed investigations of the dissolution kinetics of K-feldspar as a function of surface orientation and chemical affinity which question the commonplace belief that elementary mechanisms and resulting rate laws can be retrieved from conventional powder dissolution experiments. Nanometer-scale surface measurements evidenced that K-feldspar dissolution is an anisotropic process, where the face-specific dissolution rate satisfactorily agrees with the periodic bond chain (PBC) theory. The chemical affinity of the reaction was shown to impact differently the various faces of a single crystal, controlling the spontaneous nucleation of etch pits which, in turn, drive the dissolution process. These results were used to develop a simple numerical model which revealed that single crystal dissolution rates vary with reaction progress. Overall, these results cast doubt on the conventional protocol which is used to measure mineral dissolution rates and develop kinetic rate laws, because mineral reactivity is intimately related to the morphology of dissolving crystals, which remains totally uncontrolled in powder dissolution experiments. Beyond offering an interpretive framework to understand the large discrepancies consistently reported between sources and across space scales, the recognition of the anisotropy of crystal reactivity challenges the classical approach for modeling dissolution and weathering, and may be drawn upon to develop alternative treatments of aqueous mineral reactivity

pH-dependent control of feldspar dissolution rate by altered surface layers

Relevant modeling of mass and energy fluxes involved in pedogenesis, sequestration of atmospheric CO2 or geochemical cycling of elements partly relies on kinetic rate laws of mineral dissolution obtained in the laboratory. Deriving an accurate and unified description of mineral dissolution has therefore become a prerequisite of crucial importance. However, the impact of amorphous silica-rich surface layers on the dissolution kinetics of silicate minerals remains poorly understood, and ignored in most reactive transport codes. In the present study, the dissolution of oriented cleavage surfaces and powders of labradorite feldspar was investigated as a function of pH and time at 80 °C in batch reactors. Electron microscopy observations confirmed the formation of silica-rich surface layers on all samples. At pH = 1.5, the dissolution rate of labradorite remained constant over time. In contrast, at pH = 3, both the dissolution rates at the external layer/solution interface and the internal layer/mineral interface dramatically decreased over time. The dissolution rate at the external interface was hardly measurable after 4 weeks of reaction, and decreased by an order of magnitude at the internal interface. In another set of experiments conducted in aqueous silica-rich solutions, the stabilization of silica-rich surface layers controlled the dissolution rate of labradorite at pH = 3. The reduction of labradorite dissolution rate may result from a gradual modification of the textural properties of the amorphous surface layer at the fluid/mineral interface. The passivation of the main cleavage of labradorite feldspar was consistent with that observed on powders. Overall, our results demonstrate that the nature of the fluid/mineral interface to be considered in the rate limiting step of the process, as well as the properties of the interfacial layer (i.e. its chemical composition, structure and texture) to be taken into account for an accurate determination of the dissolution kinetics may depend on several parameters, such as pH or time. The dramatic impact of the stabilization of surface layers with increasing pH implies that the formation and the role of surface layers on dissolving feldspar minerals should be accounted for in the future

Does crystallographic anisotropy prevent the conventional treatment of aqueous mineral reactivity? A case study based on K-feldspar dissolution kinetics

International audienceWhich conceptual framework should be preferred to develop mineral dissolution rate laws, and how the aqueous mineral reactivity should be measured? For over 30 years, the classical strategy to model solid dissolution over large space and time scales has relied on so-called kinetic rate laws derived from powder dissolution experiments. In the present study, we provide detailed investigations of the dissolution kinetics of K-feldspar as a function of surface orientation and chemical affinity which question the commonplace belief that elementary mechanisms and resulting rate laws can be retrieved from conventional powder dissolution experiments. Nanometer-scale surface measurements evidenced that K-feldspar dissolution is an anisotropic process, where the face-specific dissolution rate satisfactorily agrees with the periodic bond chain (PBC) theory. The chemical affinity of the reaction was shown to impact differently the various faces of a single crystal, controlling the spontaneous nucleation of etch pits which, in turn, drive the dissolution process. These results were used to develop a simple numerical model which revealed that single crystal dissolution rates vary with reaction progress. Overall, these results cast doubt on the conventional protocol which is used to measure mineral dissolution rates and develop kinetic rate laws, because mineral reactivity is intimately related to the morphology of dissolving crystals, which remains totally uncontrolled in powder dissolution experiments. Beyond offering an interpretive framework to understand the large discrepancies consistently reported between sources and across space scales, the recognition of the anisotropy of crystal reactivity challenges the classical approach for modeling dissolution and weathering, and may be drawn upon to develop alternative treatments of aqueous mineral reactivity

The mechanism of borosilicate glass corrosion revisited

Currently accepted mechanistic models describing aqueous corrosion of borosilicate glasses are based on diffusion-controlled hydrolysis, hydration, ion exchange reactions, and subsequent re-condensation of the hydrolyzed glass network, leaving behind a residual hydrated glass or gel layer. Here, we report results of novel oxygen and silicon isotope tracer experiments with ternary Na borosilicate glasses that can be better explained by a process that involves the congruent dissolution of the glass, which is spatially and temporally coupled to the precipitation and growth of an amorphous silica layer at an inwardly moving reaction interface. Such a process is thermodynamically driven by the solubility difference between the glass and amorphous silica, and kinetically controlled by glass dissolution reactions at the reaction front, which, in turn, are controlled by the transport of water and solute elements through the growing corrosion zone. Understanding the coupling of these reactions is the key to understand the formation of laminar or more complex structural and chemical patterns observed in natural corrosion zones of ancient glasses. We suggest that these coupled processes also have to be considered to realistically model the long-term performance of silicate glasses in aqueous environments