NorCPM1 and its contribution to CMIP6 DCPP

The Norwegian Climate Prediction Model version 1 (NorCPM1) is a new research tool for performing climate reanalyses and seasonal-to-decadal climate predictions. It combines the Norwegian Earth System Model version 1 (NorESM1) – which features interactive aerosol-cloud schemes and an isopycnic-coordinate ocean component with biogeochemistry – with anomaly assimilation of SST and T/S-profile observations using the Ensemble Kalman Filter (EnKF).publishedVersio

A fractured roman glass block altered for 1800 years in seawater: Analogy with nuclear waste glass in a deep geological repository

Fractured archaeological glass blocks altered 1800 years in seawater are investigated because of their morphological analogy with vitrified nuclear waste. They provide an opportunity for understanding glass alteration in variable confined media (cracks), by studying an actual ancient system in a known stable natural environment. Characterization of the crack network from two-dimensional trace maps (length, alteration thickness, orientation) allows us to determine the three-dimensional geometric parameters (crack density, fracture ratio) and the percentage of alteration, using stereological relations. This methodology could be applied to nuclear glass. From a representative archaeological glass block, we showed that the surface developed by the cracks is 86 ± 27 times greater than the geometric surface but the volumetric alteration is 12.2 ± 4.1%, which is only 12 times greater than the volumetric alteration of the block periphery (about 1 vol%). This unexpected low value is explained by the large variation of the alteration thicknesses in the different types of cracks in relation with their location in the block. The alteration thickness is usually smaller in the internal zone than in the border zone. The alteration layers resulted from three main mechanisms (interdiffusion, glass dissolution, and secondary phase precipitation) leading to two different alteration products (a sodium-depleted layer and mainly a Mg-smectite). Geometric parameters such as the glass surface area/solution volume ratio and transport parameters (renewal of the alteration solution) strongly affected the glass dissolution kinetics. The confined conditions and the diffusive transport of reactive species favor low alteration kinetics. The precipitation of secondary phases also results in sealing of the cracks. Consequently, although it is not known if subcritical crack growth occurred, internal cracks account for only a minor contribution to the overall alteration. These results improve our understanding of alteration in cracks for assessing the predominant physical and chemical parameters that must be considered in long-term nuclear glass modeling

Behaviors of sodium and calcium ions at the borosilicate glass–water interface: Gaining new insights through an ab initio molecular dynamics study

International audienceWe study reactivity and leaching at the calcium sodium borosilicate (CNBS)–water interface by means of a Car–Parrinello ab initio molecular dynamics simulation over a simulation time of 100 ps. With an emphasis on the comparison between the behaviors of Ca$^{2+}$ and Na$^+$ cations at the CNBS glass–water interface, different mechanism events during the trajectory are revealed, discussed, and correlated with other density functional theory calculations. We show that Na$^+$ ions can be released in solution, while Ca$^{2+}$ cannot leave the surface of CNBS glass. This release is correlated with the vacancy energy of Ca$^{2+}$ and Na$^+$ cations. Here, we found that the CNBS structure with the Na$^+$ cation vacancy is energetically more favorable than the structure with the Ca$^{2+}$ cation vacancy. The calcium adsorption site has been shown to have a greater affinity for water than can be found in the case of the sodium site, demonstrating that affinity may not be considered a major factor controlling the release of cations from the glass to the solution

Behavior of B in passivating gels formed on International Simple Glass in acid and basic pH

International audienceInternational Simple Glass altered for years in silica saturated conditions develops a passivating gel, which retains some B and Ca in its the inner region. These elements could impact the way the gel limits glass alteration. However, the retention mechanism, speciation, and diffusion properties of these elements are still unknown. First, we found that the presence of B and Ca in solution can dramatically slow down glass alteration. However, splitting the B and Ca into two different solutions with other glass elements did not give similar protection against glass alteration. Further experiments in basic and acid pHs revealed that i) water diffusion is not dramatically affected by the retention of B and Ca in passivating gels, and ii) slow diffusion and high retention of B is observed only in gels formed in basic pH. This mechanism could explain how passivating gels control the residual rate

Radiation effects on the structure and alteration behavior of a SiO2_2 ‐Al2_2 O3_3 ‐B2_2 O3_3 ‐Na2_2 O glass

International audienceAs borosilicate glasses are used in many countries to immobilize fission products and minor actinides after spent fuel reprocessing before storage in a deep geological repository, assessing their chemical durability is of paramount importance. Here pristine and pre-irradiated (952MeV, 136Xe) SiO2-B2O3-Al2O3-Na2O glasses with the same molar ratios as in the French SON68 and ISG glasses have been subjected to aqueous corrosion in deionized water and in silica saturated solution to measure the initial and longer-term alteration rates. Pristine and pre-irradiated glasses corrode following the same mechanisms but the pre-irradiation has a strong impact on the initial dissolution rate (increase by a factor of 5.6), and on the alteration layer depth in silica saturated conditions (by 2–3 folds). The later result is related to the formation of a more porous, less passivating gel on the pre-irradiated glass specimen. Using both experimental spectroscopies (NMR, IR, SFG) and classical molecular dynamics, the radiation effects on the glass structure and water diffusion have been assessed. After pre-irradiation, the density and the polymerization degree of the glass decrease while the topological disorder increases. In consequence, water diffusion accelerates. These observations allow to correlate the radiation impact on the alteration behavior to the structural changes