Callovo-Oxfordian Clay Research Articles

Determination of the in situ hydraulic parameters of the Callovo–Oxfordian clay rock in a long-term hydraulic interference testing at Andra's Underground Research Laboratory (CMHM)

Abstract. Between 2009 and 2015, Andra has conducted a unique long-term hydraulic interference test in two parallel boreholes 1 m apart from each other and air core drilled in the undisturbed Oxfordian Clay rock at Andra's Underground Research Laboratory (CMHM) in Bure, France. The experimental set-up consisted of six test intervals positioned along the parallel boreholes drilled from a drift located within the Callovo–Oxfordian clay at around 500 m b.g.l. (below ground level). The 20 m boreholes were oriented around 30∘ downwards. The pressure sensors linked to six intervals of 1 m length each allowed for continuous pressure measurement over 6 years and a slanted borehole for the observation of rock displacements (see Fig. 1). Additionally, flow rates were measured during water injection tests that lasted weeks or months. This extensive set of hydraulic data allowed, for the first time, a precise determination of the in situ Callovo–Oxfordian clay rock permeability and anisotropy and its specific storage at the metre to decametre scale. It was achieved based on an automated calibration, using a 3D flow model and explicitly considering all the relevant hydraulic elements acting on the flow system (such as rock mass, borehole disturbed zone and sealing elements) and the drift acting as a steady sink due to the underground ventilation (see Fig. 2). The history matching was performed on the transient pressure measurements. The obtained numerical calibration results were in close agreement with the hydraulic parameter values of the Callovo–Oxfordian clay determined at a smaller scale (single borehole tests and rock core samples in the laboratory), therefore demonstrating the reliability of the very low permeability of the Callovo–Oxfordian clay at the metre to decametre scale. Furthermore, the modelling illustrated the impact of the measurement set-up and its details on the observed hydraulic behaviour. The analysis methodology and the main findings will be presented.

U(VI) retention in compact Callovo-Oxfordian clay stone at temperature (20–80 °C); What is the applicability of adsorption models?

In the context of the radioactive waste management in deep geological formations, U(VI) retention by intact Callovo-Oxfordian claystone (COx) was studied by percolation-type experiments at 20 and 80 °C. The experimental results were confronted with modelling prediction based on a published adsorption model developed from dispersed media in the 20–80 °C temperature range. For the experiments at 20 °C, the adsorption model allowed to explain the results for the intact system; the retention was weak (Rd ∼ 10 L•kg−1) and the analysis of the COx phases at the end of the experiment confirmed a retention of U by the clay fraction. The adsorption model in temperature also explained the observed trend of increasing retention with increasing temperature. However, it underestimated the temperature effect on the adsorption of U(VI) by the COx clay fraction, and other phases contributed to the retention. Solid-state analysis of the percolation-doped samples indicated a reactivity in the order pyrite>clay>calcite phases. The transposition of the knowledge at 20 °C from the dispersed system to the intact medium was therefore not possible at 80 °C for the studied U(VI)/COx system.

Temperature effect of U(VI) retention on the Callovo-Oxfordian clay rock

In the context of management of the radioactive waste in deep geological formations, the effect of temperature (20–80 °C) on U(VI) adsorption by Callovo-Oxfordian claystone (COx) was studied. A step-by-step approach was followed, starting with the single mineral, illite, followed by an increase in the complexity of the system, through the analysis of the clay fraction and the natural samples of the Callovo-Oxfordian formation. Depending on the study conditions, and the speciation of U(VI) in solution (hydrolysed species, carbonate species and presence of ternary U(VI)-Ca(Mg)‑carbonate complexes), the temperature effect was either negligible, or positive (where the increase in temperature favours retention). The most important positive effect was observed for the U(VI)/COx system in the presence of ternary complexes. The data were modelled considering an existing sorption model at 20 °C and the thermodynamic data available to describe the evolution of the speciation of U(VI) in solution in function of temperature. The enthalpy values associated with the surface complexes were fitted from the experimental data following a stepwise approach based on the van't Hoff equation.

Boom Clay pore-water geochemistry at the Mol site: Chemical equilibrium constraints on the concentrations of major elements

It is important to understand the mechanisms controlling the chemistry of the pore water in the Boom Clay, which has been studied as a reference host rock for the geological disposal of radioactive waste. The chemistry of the pore water and the related properties of the Boom Clay were investigated experimentally. This paper presents the results of equilibrium calculations and discusses the probable chemical constraints that control the concentrations of major elements in the pore water. The present-day Boom Clay pore water is a dilute NaHCO3 solution of 10–20 mM, and the concentration increases with the depth of the Boom Clay over a thickness of 65 m around the underground laboratory at approximately 200 m below sea level. The present-day NaHCO3 water is likely a result of freshwater infiltration, and the concentration profile observed must have been affected by waters from upper and lower aquifers. Among the minerals found in the Boom Clay, equilibrium calculations indicate that the pore water is in equilibrium with calcite, dolomite, siderite, pyrite, and quartz. Aluminium silicate minerals, kaolinite and chlorite, are also possibly in equilibrium, but their saturation states cannot be fully demonstrated mainly because of uncertainties associated with the pore-water concentration of aluminium. Cation exchange, an important property of clays, seems to be controlling only the pore-water concentration of potassium. Concentrations of other cation exchangeable elements, such as calcium and magnesium, are more likely regulated by the solubility of carbonate minerals. On clay surfaces, however, cation-exchange reactions are evidenced and control occupancies of all exchangeable cations. The cation-exchange pool on clay responds to the increase in NaHCO3 concentration with depth, and the surface occupancies vary according to the selectivity of exchangeable cations. Equilibrium calculations allow us to propose a Boom Clay reference model that is able to explain the observed pore-water chemistry. This model is compared to other models in the literature, such as those for the Opalinus Clay in Switzerland and Callovo-Oxfordian Clay in France, which have also been studied for the purpose of radioactive waste disposal. Future studies to improve our understanding of the Boom Clay pore-water geochemistry include i) accurate determination of the pore-water concentration of aluminium, which is crucial for studying the mineral saturation state of aluminium silicates; ii) improving understanding of the mineralogical composition of dolomite in the Boom Clay and its dissolution mechanisms; iii) reassessment of magnesium cation-exchange occupancy on clay surfaces; and iv) improving pore-water sampling and analysis techniques with respect to pH and pCO2 measurements to avoid perturbations to water samples so that the in situ conditions can be preserved to a maximum extent.

THM Response in the Near Field of an HLW Disposal Tunnel in the Callovo-Oxfordian Clay Host Rock Caused by the Imposed Heat Flux at Different Water Drainage Conditions

Heat load from high-level radioactive waste (HLW) packages will result in elevated temperatures around the disposal tunnel. Differences in thermal expansion between rock and water will induce the redistribution of stresses. The assessment of the thermo-hydromechanical (THM) regime is necessary to evaluate the potential for fracture development. For this purpose, it is important to evaluate the nature and extent of induced strains, and their impact on rock permeability, which, subsequently, is important for radionuclide transport. This paper presents the modeling activities of the Lithuanian Energy Institute performed in the framework of the European joint program EURAD and the analysis of the influence of temperature on clay-based material behavior. Within this study, different stress conditions and material properties (isotropic, anisotropic) were analyzed with a thermo-poroelastic material model for the Callovo-Oxfordian clay host rock in the 100 m × 100 m domain. The heat load on the clay rock comes from a tunnel with a radius of 1.25 m. The overall THM response of the clay host rock system to the heat load is performed with the COMSOL Multiphysics (Burlington, MA, USA) software. The THM response near the HLW disposal tunnel was analyzed in terms of temperature, pore pressure, displacements, and stresses, and the results are presented in this work. Besides the impact of anisotropy, the effect of hydraulic conditions at the tunnel boundary was also analyzed. The modeling results revealed that anisotropy in stress and properties had an impact on the hydro-mechanical response of the material even during excavation and waiting phases. The analysis also showed that the water drainage condition on the tunnel boundary had no effect on the thermal state around the tunnel, but it had a significant impact on the hydro-mechanical response.

The contribution of swelling to self-sealing of claystone studied through x-ray tomography

Many countries, as among others France, Belgium and Switzerland, are facing the issue of finding a proper solution to store radioactive waste coming from nuclear power plants. The possibility to store them in underground tunnels is largely considered and investigated. In France, Andra (Agence Nationale pour la gestion des Déchets RAdioactifs) selected the Callovo-Oxfordian clay rock situated in the Meuse/Haute Marne site between 400 and 600 m depth as possible host rock deposit. The excavation of the storage tunnels is expected to create a fractured zone around galleries. The factures will be then gradually re-saturated by the underground water coming from the surrounding rock and they are expected to self-seal in contact with water, thanks to the swelling potential of COx. The capacity of self-sealing, i.e. closing of fractures after water contact and possibly restoring of permeability, is thus of primary interest for the safety of the storage system with respect to water, gas and solutes transport. The physical mechanisms driving this phenomenon are mainly the swelling and de-structuration of the clay matrix present in the claystone. In this work, the self-sealing response of COx was investigated through x-ray tomography at multi-micrometre and sub-micrometre voxel size. The objective was to study the influence of mineralogy, size of the discontinuity, hydraulic paths, mutual orientation of the bedding plane and fractures. The size of the discontinuity is of primary importance in determining the percentage of closure. Fractures parallel to the bedding plane are more likely to seal as swelling is anisotropic and occurs mainly perpendicular to the bedding plane. The main novelty is represented by the direct and local observation of the physical process of self-sealing down to a scale lower than 1 μm.

Uranium retention in a Callovo-Oxfordian clay rock formation: From laboratory-based models to in natura conditions

For the performance assessment of radioactive waste disposal, it is critical to predict the mobility of radionuclides in the geological barrier that hosts it. A key challenge consists of assessing the transferability of current knowledge on the retention properties deduced from model systems to in natura situations. The case of the redox-sensitive element uranium in the Callovo-Oxfordian clay formation (COx) is presented herein. Extensive experimental work was carried out with respect to parameters affecting uranium speciation (pH, PCO2, [Ca] and redox potential) with illite, COx clay fraction and raw COx claystone. The “bottom-up” approach implemented, with illite and montmorillonite as reactive phases, quantitatively explains the adsorption results of U(VI) and U(IV) on COx. While retention is high for U(IV) (Rd∼104 L kg−1), it remains very low for U(VI) (Rd∼4 L kg−1) due to the formation of soluble ternary Ca(Mg)–U(VI)-carbonate complexes. The applicability of the sorption model was then assessed by comparing predictive analyses with data characterizing the behavior of naturally-occurring U (<3 mg kg−1). The COx clay phase is the largest reservoir of naturally-occurring U (∼65%) but only a small fraction appears to be adsorbed (∼1%). Under representative site conditions (especially with respect to reducing conditions), we have concluded that ternary U(VI) complexes control U speciation in solution while U(IV) surface species dominate U adsorption, with Rd values > 70 L kg−1.

The Callovo-Oxfordian as sand substitution in concrete: Effect on the confinement of the ion exchange resin

The present work aims to investigate the conditions for improving the containment of spent ion exchange resin (IER) as a radioactive waste, using powdered Callovo-Oxfordian clay (COx) as an addition to the cementitious matrix at different rates. The aim of this work was to investigate the influence of COx on the characteristics of cemented packages of spent (REI). In this context, a cemented pack was made using Portland class 45 cement, sand, resin and water. And others are prepared by replacing the sand with COx, in the following proportions: (2%, 4%, 6%, 8% and 10%). The packages obtained with and without COx were measured for their compressive strength and porosity.

Nickel Retention on Callovo-Oxfordian Clay: Applicability of Existing Adsorption Models for Dilute Systems to Real Compact Rock.

In a waste management context, predicting the mobility of contaminants is essential. A key issue entails assessing the applicability of current knowledge on adsorption processes to natural systems. Such is the focus herein for nickel in interaction with Callovo-Oxfordian (COx) clay rock, a formation selected in France for possible radioactive waste disposal. The challenge is to link predictive modeling results with the experimental data characterizing the behavior of the labile and naturally occurring Ni fraction by implementing a new simple method. Retention studies on compact systems serve to complete this work. Combined electron microprobe and laser ablation high-resolution inductively coupled plasma mass spectrometry data show that natural Ni (∼39 mg kg-1) is homogeneously distributed within the clay matrix, which corresponds to the main reservoir (∼70%). Data interpretation of desorption tests yields an in situ Kd value of ∼80 L kg-1 and a labile Ni amount of ∼5 mg kg-1, that is, ∼13% of the Ni inventory. Predictive modeling explains the sorption data in considering that only weak clay fraction sites take part in the adsorption. The role of the clay matrix in Ni retention is confirmed by analyzing the Ni-spiked compact COx samples, whereby an increase of the Ni content in the clay fraction is observed following the retention experiment.

Investigation on anisotropy of mechanical properties of Callovo-Oxfordian claystone

Anisotropic mechanical properties of the sedimentary Callovo-Oxfordian clay rock were investigated with triaxial compression and extension, cyclic compression, and creep tests. The tested cylindrical samples differ in bedding orientation. The compression was accomplished by increasing axial stress at constant radial stress. The extension was carried out vice versa: radial stress was increased while axial stress was kept constant. Moreover, extension was also achieved by simultaneously increasing radial stress and decreasing axial stress under constant mean stress. Five independent elastic parameters were obtained at different deviatoric stresses during cyclic loading-unloading compressions. The deformation and strength were determined in relation to the load direction inclined to bedding and in relation to the load paths. The claystone exhibits elastoplastic stress-strain behaviour with volume compaction until failure. The strength is dependent on both load path and load direction to the bedding. For a given major load direction, the compressive strength is higher than the extensional one and the lowest strength occurs by extension at constant mean stress. In each load path, the maximum strength values are reached parallel and normal to the bedding, while the minimum occurs at the load orientation of about 45° during compression and of about 30° during extension. The elastic stiffness increases with deviatoric loading due to hardening. The deformability is time dependent.

Sealing behaviour of crushed claystone–bentonite mixtures

Crushed claystone mixed with bentonite as a potential material for sealing repositories was extensively investigated. The crushed claystone excavated from the Callovo-Oxfordian clay rock was mixed with bentonite MX80 obtaining a bentonite content of 20% and 40% and compared to pure bentonite and a bentonite–sand (70/30) mixture with respect to relevant sealing properties. These materials were compacted to pre-determined densities and their properties were characterised with respect to compacted density and porosity, mechanical stiffness and stability, water uptake and retention, swelling capacity, water permeability, and gas migration. Main findings include that 1) higher dry densities are achieved with claystone–bentonite mixtures than pure bentonite and bentonite–sand mixture under identical compression loads, which increases mechanical stiffness and stability; 2) the swelling capacity increases with increasing bentonite content and dry density of the mixtures; 3) all the compacted mixtures have low water permeabilities of 10−19 –10−20 m2 being in the same order as intact claystone; and 4) the compacted claystone–bentonite mixtures allow for gas release already at low and moderate pressures, while in contrast high pressures are needed for gas penetrating water-saturated bentonite and bentonite–sand mixtures.

Deformation in cemented mudrock (Callovo–Oxfordian Clay) by microcracking, granular flow and phyllosilicate plasticity: insights from triaxial deformation, broad ion beam polishing and scanning electron microscopy

Abstract. The macroscopic description of deformation and fluid flow in mudrocks can be improved by a better understanding of microphysical deformation mechanisms. Here we use a combination of scanning electron microscopy (SEM) and broad ion beam (BIB) polishing to study the evolution of microstructure in samples of triaxially deformed Callovo–Oxfordian Clay. Digital image correlation (DIC) was used to measure strain field in the samples and as a guide to select regions of interest in the sample for BIB–SEM analysis. Microstructures show evidence for dominantly cataclastic and minor crystal plastic mechanisms (intergranular, transgranular, intragranular cracking, grain rotation, clay particle bending) down to the nanometre scale. At low strain, the dilatant fabric contains individually recognisable open fractures, while at high strain the reworked clay gouge also contains broken non-clay grains and smaller pores than the undeformed material, resealing the initial fracture porosity.

The Dependency of Diffusion Coefficients and Geometric Factor on the Size of the Diffusing Molecule: Observations for Different Clay-Based Materials

In order to investigate in more detail the relation between the size of diffusing molecules and their diffusion coefficients (and geometric factors), diffusion experiments with gases of different size and tritiated water (HTO) have been performed on different clayey samples (Boom Clay, Eigenbilzen Sands, Opalinus Clay, Callovo-Oxfordian Clay, and bentonite with different dry densities). We observed that, for unreactive gases in clayey materials, the effective diffusion coefficient varies with the size of the diffusing molecule and this variation can be described by an exponential or a power law function. The variation of the geometric factor can also be described by an exponential function. The observed experimental relations can be used to estimate diffusion coefficients; by measuring experimentally in clay the effective diffusion coefficient of two unreactive dissolved gases with a different size, the diffusion coefficients of other dissolved gases (with a size in between the two measured gases) can be estimated by using the fitted exponential relationship.

Interaction of Ions with Hydrated Clay Surfaces: Computational Molecular Modeling for Nuclear Waste Disposal Applications

The Callovo-Oxfordian clay formation (COx) is the potential host rock for long term nuclear waste repository in France. The clayey component of COx consists mostly of illite, smectite and interstratified illite/smectite (I/S) clay minerals. We performed a series of molecular dynamics (MD) computer simulations in order to quantify the molecular scale mechanisms responsible for the adsorption and transport of ions at the hydrated surfaces of illite, smectite, and I/S clays. New structural models of illite, smectite, and I/S allowed us to identify several structurally different adsorption sites at the basal surfaces of all three clay substrates. Adsorption free energy profiles above each individual adsorption site on each clay surface for a wide range of metal cations were then calculated and the metal sorption properties for the three clay surfaces are compared in terms of the preferable sorption sites and their surface distributions, most stable adsorption distances, and free energies of adsorption. The resulting equilibrium constants for surface adsorption and ion exchange were calculated and found in general agreement with available literature data. The observed discrepancies between the exchange energies obtained in the current MD simulations and the values obtained through the interpretation of recent X-ray reflectivity measurements can be attributed to the differences in the description of the exchange reaction equilibria between the experimental conditions and the simplified conditions of our simulations.

Competitive Adsorption of Organic Molecules on Clay Rock

The processes governing adsorption of anthropogenic organic molecules on natural systems are complex. The presence of various phases in soils and mudstones may lead to various and simultaneous retention mechanisms. Adsorption experiments were performed on acetic, o-phthalic and citric acids on the Callovo-Oxfordian clay rock. Whereas the retention of inorganic species is dominated by clay minerals, small carboxylic acids were found to sorb on various phases or sites and not necessarily endured competition during co-adsorption. Data will be presented to illustrate the interest of various adsorption protocols to discriminate between mechanisms occurring beside adsorption onto soils and sediments: covalent bounding, chemical perturbation, phase dissolution, bacterial activity, etc..

Measuring diffusion coefficients of dissolved He and Ar in three potential clay host formations: Boom Clay, Callovo-Oxfordian Clay and Opalinus Clay

Abstract For the long-term management of high- and intermediate-level radioactive waste and/or spent fuel, many countries prefer disposal in a geological repository. In Belgium, Switzerland and France, argillaceous formations are being explored as potential host formations for this purpose. In this context, knowledge of the diffusion coefficient of He is relevant within two research areas: first, diffusion coefficients are used in safety calculations to evaluate the balance between gas generation (mainly H 2 ) and gas dissipation; and, second, the diffusion coefficients of He and Ar are needed in the diffusion models of natural tracers. Owing to the lack of data on the diffusion coefficients of He and Ar for the different clay host formations, diffusion experiments with dissolved He and Ar were performed on Boom Clay, Opalinus Clay and Callovo-Oxfordian Clay. Samples were confined in a diffusion cell, and diffusion coefficients were measured by using the double through-diffusion technique. The diffusion coefficients ( D p or D pore ) for He in Boom Clay, Callovo-Oxfordian Clay and Opalinus Clay are 12.6×10 −10 , 4.51×10 −10 and 7.13×10 −10 m 2 s −1 , respectively. The diffusion coefficients for Ar in Boom Clay, Callovo-Oxfordian Clay and Opalinus Clay are 18.6×10 −11 , 4.06×10 −11 and 3.65×10 −11 m 2 s −1 , respectively.

The stress–strain–permeability behaviour of clay rock during damage and recompaction

Characterisation and understanding of the stress–strain–permeability behaviour of a clay host rock during damage and recompaction are essential for prediction of excavation damaged zone and for assessment of its impact on the repository safety. This important issue has been experimentally studied in triaxial compression tests on the Callovo-Oxfordian clay rock in this study. The samples were sequentially loaded by (1) hydrostatic precompaction to close up sampling-induced microcracks, (2) applying deviatoric stresses to determine damage and permeability changes, and (3) recompression along different loading paths to examine reversibility of the damage. The critical stress conditions at the onset of dilatancy, permeability percolation, failure strength, and residual strength are determined. An empirical model is established for fracturing-induced permeability by considering the effects of connectivity and conductivity of microcracks. The cubic law is validated for the variation of permeability of connected fractures with closure. The experiments and results are also presented and discussed.

Thermanaeromonas burensis sp. nov., a thermophilic anaerobe isolated from a subterranean clay environment.

A strictly anaerobic, thermophilic and halotolerant strain, designated IA106T, was isolated from the seepage water collected in a metal biocorrosion test at a depth of 490 m, in a 130-160 m thick, subterranean Callovo-Oxfordian clay formation (158-152 million years old) in northern France. This geological formation has been selected as the potential host rock for the French high-level nuclear waste repository. Cells of strain IA106T stained Gram-positive and were non-motile, spore-forming, straight rods (0.5 × 2-6 μm). The five major fatty acids were C16 : 0 (15.9 %), C18 : 0 (15.4 %), iso-C17 : 1 I and/or anteiso-C17 : 1 B(14.8 %), iso-C17 : 0 (14.7 %) and iso-C15 : 0 (13.0 %). Growth was observed at temperatures ranging from 55 to 70 °C and at pH 5.5-9. The salinity range for growth was 0-20 g NaCl 1- 1. Yeast extract was required for growth. Strain IA106T was able to grow on lactate and various sugars in the presence of thiosulfate as electron acceptor. Sulfate, sulfite, elemental sulfur, fumarate, nitrate and nitrite were not reduced. The DNA G+C content was 60.2 mol%. 16S rRNA gene sequence analysis indicated that strain IA106T belonged to the family Thermoanaerobacteraceae, class Clostridia, phylum Firmicutes, and was most closely related to Thermanaeromonas toyohensis DSM 14490T (95.16 % 16S rRNA gene sequence similarity). On the basis of 16S rRNA gene sequence comparisons and physiological characteristics, strain IA106T represents a novel species of the genus Thermanaeromonas, for which the name Thermanaeromonas burensis sp. nov. is proposed. The type strain is IA106T ( = DSM 26576T = JCM 18718T).

Meuse/Haute-Marne centre: next steps towards a deep disposal facility

This paper presents the main results obtained during a decade of scientific activities in the Meuse/Haute-Marne Underground Research Laboratory (URL) located on the eastern boundary of the Paris Basin, in the Callovo-Oxfordian clay rock formation. The URL was built in the framework of ANDRA’s research program into the feasibility of a reversible deep geological disposal of high-level and intermediate-level long-lived radioactive (HL, ILLL) waste. Its underground drifts have been used to study a 160-million-year old clay layer. The 2006 Planning Act adopted this disposal concept as the reference solution for the long-term management of HL and ILLL radioactive waste. Today, research is continuing into the design and sitting of the disposal facility which could be commissioned by 2025 if its license is granted in 2016. Through these programs, the laboratory will help ANDRA develop a concrete approach with a view to proposing suitable architectures and management methods for a deep disposal facility, to allow by 2016 the decision for the start of the construction of the shafts and drifts of the new disposal facility.

On corrosion of carbon steels in Callovo-Oxfordian clay: complementary EIS, gravimetric and structural study providing insights on long term behaviour in French geological disposal conditions

Dedicated integrated experiments have been used to determine in situ the corrosion rate of carbon steels in geological repository mock-ups (90°C, anaerobic, slow synthetic water flux…). Electrochemical impedance spectroscopy (EIS) measurements were performed, allowing for the extraction of instantaneous corrosion rate. In a separate but comparable set-up, occasional sampling among a batch of fifteen equivalent cells was performed, allowing for both gravimetric measurements and corrosion products characterisation. In both cases, the corrosion rate decreases continuously but the stationary state seems not to be reached within the duration of the EIS experiment. The slow kinetics and pseudo steady state of the corrosion process are confirmed by post-exposure characterisation of the corrosion products by SEM, micro-Raman spectroscopy and micro-XRD, revealing the rapid formation of an iron phyllosilicate layer that may act as a barrier layer for diffusion of the species between the clay environment and the alloy. This analysis provides good confidence on long term (over a millennium) extrapolations made from the experimental data fits, leading to an estimation of reasonable cumulated damages in the [40;120] μm range after 1000 years exposure.