Modelling of Predictive Hydraulic Impacts of a Potential Radioactive Waste Geological Repository on the Meuse/Haute-Marne Multilayered Aquifer System (France)

The French National Agency for Nuclear Waste Management (Andra) conducted a site investiga- tions program within the project of a deep geological disposal of radioactive waste in the Meuse/ Haute-Marne region. The construction of the tunnel of 5 Km length and the shafts of about 500 m depth to access the repository located in the clay host formation of Callovo-Oxfordian age, will lead to the perturbations of the groundwater flow fields. The prediction of the behaviour of these perturbations is needed to support: 1) the engineering and monitoring operations, and 2) the assessment of the consequences on groundwater resources. A variably-saturated flow model of a local multi-layered aquifer system is developed. It integrates the Oxfordian aquifer (limestone), the Kimmeridgianaquitard (marl) and the Barrois limestone aquifer including the karst conduits network. The variably-saturated flow Richard’s equation is solved with a finite element simulator. Prior to the simulation of the predictive repository impacts, a transient flow model is calibrated with respect to Underground Research Laboratory (URL) construction data. The results are analysed and evaluated by the use of performance measures.

Cartography of Landslide Susceptibility around the Dias Horst and Thies Cliff-Senegal

The aim of this work is to map the susceptibility of sites to landslides. To assess the susceptibility of the zone, GIS techniques were used. Susceptibility factors are selected and split into two groups: active and passive factors. Passive factors regroup all the intrinsic conditions existing on the field at all times. The active factors or triggering factors are present sporadically and are added to the passive factors to trigger a landslide. With the weighted overlay method using ArcGIS?, four scenarios have been developed. A first scenario where only passive factors are combined and three scenarios for which we have for each scenario the passive factors combined with an active factor. With these different scenarios, five levels of susceptibility are obtained in the zone. These levels range from very low to very high susceptibility. For the different scenarios, the results show that the zone consists mainly of very low to low susceptibility with at least 61% of the area, followed by moderate susceptibility (23.54% to 38.24%) and last land with high susceptibility to very high with less than 1% of the surface. Fields with high to very high susceptibility are located on the slopes of the hills. Among the active factors, only the rainfall significantly modifies the percentage of land susceptible to landslide but remains in the field of moderate susceptibility. The predicted susceptibilities are closer to the observed landslides around the Thies Cliff than to the Dias Horst.

On the origin of the high tensile strength and ductility of additively manufactured 316L stainless steel: Multiscale investigation

We report that 316L austenitic stainless steel fabricated by direct laser deposition(DLD),an additive manufacturing(AM)process,have a higher yield strength than that of conventional 316L while keeping high ductility.More interestingly,no clear anisotropy in tensile properties was observed between the building and the scanning direction of the 3D printed steel.Metallographic examination of the as-built parts shows a heterogeneous solidification cellular microstructure.Transmission electron microscopy observations coupled with Energy Dispersive X-ray Spectrometry(EDS)reveal the presence of chemical micro-segregation correlated with high dislocation density at cell boundaries as well as the in-situ formation of well-dispersed oxides and transition-metal-rich precipitates.The hierarchical heterogeneous microstructure in the AM parts induces excellent strength of the 316L stainless steel while the low staking fault energy of the as-built 316L promotes the occurrence of abundant deformation twinning,in the origin of the high ductility of the AM steel.Without additional post-process treatments,the AM 316L proves that it can be used as a structural material or component for repair in mechanical construction.

Influences of graphene nanoplatelet aspect ratio and thermal treatment on dielectric performances of poly(methyl methacrylate)composites

The dielectric property and percolated behaviour of polymer matrix composites largely depend on the morphology of conductive fillers and external stimulations especially when the composites are processed by melting blending and extrusion-injection way.In this study,the poly(methyl methacrylate)(PMMA)matrix composites incorporated by two kinds of graphene nanoplatelets(GNP),G5 and G150 with different aspect ratios(the ratio of diameter and thickness)are prepared to study the influence of GNP morphology on the dielectric performances close to percolation threshold(f_(c)).After annealing at glass transition temperature(T_(g))for 1 h,the dielectric permittivities of PMMA/G5 and PMMA/G150 near fc increase 43 and 38%,respectively,while the dielectric loss change little.This improvement on the dielectric property is possibly attributed to the slight change of the distance between adjacent GNPs after annealing at T_(g)which enables to arouse stronger polarisation by tunnelling effect.

Typical synergistic effect of graphite nanoplatelets and carbon nanotubes and its influence on polymer-based dielectric composites

Graphite nanoplatelets(GNPs)with their intrinsic two-dimensional structure make an excellent compromise of advantages of both graphite and graphene.Due to their outstanding inherent properties,GNPs have been widely used as the functional fillers to improve certain performances of polymer-based composites.However,the multi-layer stacked construction of GNPs could form aggregations easily,which limits their application in polymer-based dielectric composites.Here,the authors exhibit a polydimethylsilicone(PDMS)-based nanocomposite which loading equivalent carbon nanotubes(CNTs)and GNPs as co-loading fillers,whose dielectric properties are improved significantly.The composites were fabricated through a highly-shearing mechanical mixing process.During the mixing process,both intrinsic CNTs entanglements and GNPs stacked aggregation could be ameliorated due to the interaction between these two types of fillers.Compared with the GNPs solely loaded composites,a small quantity of CNTs addition endows GNPs/CNTs/PDMS ternary composites with a significantly decreased percolation threshold(f_(c)∼1.7 vol.%).Both GNPs and CNTs,these two representative conductive carbon constructions with high aspect ratios are able to effectively enhance the establishing efficiency of internal conductive network inner composites.These results indicate that the development of internal conductive network and dielectric performance of nanocomposites are able to be optimised through the strategy of taking advantage of the synergistic effect of multi-type fillers reasonably.