Pratiques paysannes d'exploitation des arbres et paysages forestiers dans le Haut Atlas central

Dans le Haut Atlas marocain, les sociétés rurales berbères ont mis en place des systèmes de gestion endogènes qui ont permis de maintenir la disponibilité des ressources forestières et pastorales sur le temps long, notamment parla pratique de l'agdal. Celle-ci correspond à l'instauration de mises en défens temporaires sur des territoires bien définis et l'élaboration de règles d'usages pour des ayants droit bien identifiés. Les modalités des règles et des pratiques d'usages qui en découlent ont des incidences directes sur les formes des arbres et la structure des peuplements forestiers. On assiste ainsi à un façonnage de paysages diversifiés au sein d'une forêt rurale qui répond à des modes de vie et des besoins qui intègrent production,conservation et gestion des aléas d'un milieu montagnard contraignant au sein de dimensions sociales, politiques et spirituelles propres aux sociétés locales qui les ont pensées

OSCAR-Na: A New Code for Simulating Corrosion Product Contamination in SFR

International audienceA code named OSCAR-Na has been developed to calculate the mass transfer of corrosion products in the primary circuit of sodium fast reactors (SFR). It is based on a solution/precipitation model, including diffusion in the steel (enhanced under irradiation), diffusion through the sodium boundary layer, equilibrium concentration of each element and velocity of the interface (bulk corrosion or deposition). The code uses a numerical method for solving the diffusion equation in the steel and the complete mass balance in sodium for all elements. Corrosion and deposition rates are mainly determined by the iron equilibrium concentration in sodium and its oxygen enhanced dissolution rate. All parameters of the model have been assessed from a literature review, but iron solubility had to be adjusted. A simplified primary system description of PHENIX French SFR was able to assess the correct amounts and profiles of contamination on heat exchanger surfaces for the main radionuclides

Experimental study of particle deposition kinetics in the primary circuit of the CIRENE loop and comparison with OSCAR V1.2 code simulations

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The OSCAR code package : A unique tool for simulating PWR contamination

International audienceUnderstanding the PWR primary circuit contamination by corrosion products, fission productsand actinides is a crucial issue for reactor operation and design. The main challenges aredecreasing the impact on personnel exposure to radiation, optimizing the plant operation,limiting the activity of the wastes produced during the reactor lifetime and preparingdecommissioning.In cooperation with EDF and AREVA NP, CEA has developed the OSCAR code package, aunique tool for simulating PWR contamination. The OSCAR package results from the mergingof two codes, which simulate PWR contamination by fission products and actinides (PROFIPcode) and by activated corrosion products (PACTOLE code).These two codes have been validated separately against an extensive set of data obtained over 40years from in-situ gamma spectrometry measurements, sampling and analysing campaigns ofprimary coolant, as well as experiments in test loops or experimental reactors, which arerepresentative of PWR conditions.In this paper, a new step is presented with the OSCAR code package, combining the features ofthe two codes and motivated by the fact that, wherever they originate from, the contaminationproducts are subject to the same severe conditions (300 °C, 150 bar, neutron flux, water velocityup to 15 m.s-1) and follow the same transport mechanisms in the primary circuit. The main processes involved are erosion/deposition, dissolution/precipitation, adsorption/desorption,convection, purification, neutron activation, radioactive decrease.The V1.1 version of the OSCAR package is qualified for fission products (Xe, Kr, I, Sr),actinides (U, Np, Pu, Am, Cm) and corrosion products (Ni, Fe, Co, Cr).This paper presents the different release modes (defective fuel rod release, fissile materialdissemination, material corrosion and release), then the processes which govern contaminationtransfer, and finally, we give examples of the comparison of the OSCAR package results withmeasurements in French PWR primary circuit obtained for representative radioisotopes : $^{133}$Xe,$^{90}$Sr, $^{58}$Co, $^{60}$Co. In particular, we focus on the main upgrades in the OSCAR simulations compared to thePROFIP and PACTOLE codes : adaptation of the MARGARET module to assess fission productrelease out of fuel pellets in a defective rod, adsorption/desorption model development forstrontium behaviour, multi-criteria calibration of input data which are not well known forcorrosion product simulation