Evaluation of the chemical compatibility of SiC/SiC composite materials in nuclear environments

International audienc

Thermomechanical compatibility of SiC/SiC composites as structural materials for Sodium-cooled Fast Reactors

International audienc

Determination of mass transfer coefficient in flow assisted corrosion of steel in liquid Pb Bi. Rotating cylinder geometry

International audienceThe aim of this experimental and numerical work is to determine the mass transfer at the wall of a steel cylinder rotating within liquid Lead-Bismuth blend. This is a crucial parameter for the analysis of corrosion tests performed in the CICLAD experimental setup for the investigation of flow assisted corrosion of steel by liquid metals. As a reliable numerical modelling must rely on experimental validation, and since no direct wall mass transfer measurement is possible in CICLAD, a scaled electrochemical model has been achieved. Modelling the turbulence in this rotating configuration is shown to require the use of a Reynolds-Stress Model. A sensitivity to the Schmidt number is observed in the numerical simulations representing the measured mass transfer in the electrochemical model. Simulations dedicated to liquid Pb-Bi are thus presented in addition to those dedicated to the aqueous solution used in the electrochemical model. Following correlations are proposed for the prediction of Fe mass transfer at the wall of a steel rotating cylinder in liquid Pb-Bi: Sh=1.9x10-1 (Re 2 Sc) 0.31 for 2x10 9 <Re 2 Sc<5.3x10 10 ; Sh=1.4x10-3 (Re 2 Sc) 0.51 for 5.3x10 10 <Re 2 Sc<8.5x10 11

Corrosion of T91 and pure iron in flowing and static Pb-Bi alloy between 450&#8239;°C and 540&#8239;°C: experiments, modelling and mechanism

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Corrosion of Fe-9Cr Steels in Sodium Fast Reactors Environments

The sodium cooled fast reactor is selected by France as the most mature GEN IV concept to be industrially developed by the year 2040. A collaborative research program has been established together with EDF and Areva NP. In this program, different innovations are being considered in the design of the reactor leading to the use of various environments apart from liquid sodium and water vapor encountered in the “classical” sodium fast reactors. As a matter of fact, considerations on the suppression of the water-sodium reaction risk led to the proposal of the use of alternative coolants such as Pb-Bi involving an intermediate circuit between the primary sodium and the steam generator. Other concepts involve the use of supercritical CO2 instead of water vapor in the energy conversion system. In all cases, structural materials encounter severe conditions regarding corrosion concerns: high temperatures and possibly aggressive chemical environments. In this paper, status of the research performed in CEA on the corrosion behavior of the structural material and especially Fe-9Cr steels is presented in the various environments: sodium (see paper by JL Courouau), Pb-Bi, water vapor and CO2. The materials studied are metallic materials: austenitic and ferrito-martensitic steels as well as ODS steels as an option for the cladding material. In the different environments studied, the scientific approach is identical, the objective being in all cases the understanding of the corrosion processes to establish recommendations on the chemistry control of the coolant and to predict the long term behavior of the materials by the development of corrosion models. First, the corrosion mechanisms are analyzed using dedicated experimental devices. As a matter of fact, the complex environments require also controlled, safe and precise experimental systems to perform long duration corrosion tests (several thousands of hours). Therefore, specific experiments, adapted to each corrosive medium, are carried out in the laboratory. For example: - laboratory scale loops are used for liquid metals corrosion studies (use of rotating cylinders to simulate high turbulent conditions), - thermogravimetric analyses are also used to perform gas corrosion studies in representative temperature and environmental conditions,… Then, multi-scale characterization of the materials studied is performed (FEG-SEM, EDX, XRD, GD-OES…), together with precise analyses of the environments tested (in situ measurements with specific probes, gas chromatography…). Corrosion mechanisms are then proposed and models developed, depending on the advancement and the maturity of the program

Investigation of tailored SiC/SiC composites for Sodium-cooled Fast Reactors

International audienceIncreasing the sustainability and the safety ofnuclear reactors require the development of new types ofreactors (GEN-IV systems) which can work as breeder(producing more fuel that it consumes) and can offer thepossibility of burning minor actinides to reduce the waste,such as the Sodium- (SFR) or the Gas-cooled (GFR) FastReactors. Therefore, there is a need to assess materialswhich can withstand these very harsh core conditions. Inthis aim, SiC/SiC composites are promising candidatesthanks to their high decomposition temperature(> 2000°C), low swelling and creep under irradiation andgood neutron transparency. A recent CEA patent hashighlighted that SiC/SiC-based hexagonal tubes wouldincrease the resistance to melting and, as a consequence,the safety of the SFR core. In this way, techniques havebeen developed to manufacture a SiC/SiC hexagonal tubewith given dimensions, which has a relatively low level ofporosities and a pseudo-ductile mechanical behavior(tolerance to deformation). Besides, the chemicalcompatibility between SiC and SiC/SiC compositestowards liquid sodium and its impurities (in particularoxygen) was investigated. For this purpose, two sets ofexperiments were conducted in the CORRON$^2$facility(CEA). On the one hand, immersions up to 2000h in anoxygen-purified ([O]<10ppm) liquid sodium heated up tothe nominal temperature of a SFR (550°C) were carriedout. On the other hand, oxygen was inserted in the liquidsodium to reach important oxygen quantities($[O]$ = $1000\ ppm$), well above the reference consideredfor incidental and transient states, to investigate theinfluence of this element on the SiC/SiC composites.Indeed, the SiC/SiC composites and their pyrocarboninterphase (employed to have a good linkage between thefiber and the matrix) can encounter active or passiveoxidation at high temperatures. Mass assessments, SEM,XPS, X-ray tomography and tensile tests were conductedto characterize the sample properties before and afterimmersion. As a result, it was observed that there is nosignificant degradation of the material after exposure toeither the oxygen–poor or –rich environments. Moreover,in some cases, an increase of the mechanical properties ofSiC/SiC composites was observed

Modeling the environmental susceptibility of landfill sites in California

​​The proper management of solid waste (SW) is a global environmental challenge. A major issue is the proper disposal of SW while balancing a wide range of criteria and working with different spatial data. In this study, we used geographic information system as a tool to perform multi-criteria decision analysis with an analytical hierarchy process to develop an environmental impact susceptibility model (EISM) for landfills. The model was applied to the state of California, USA and results are presented herein. In particular, the EISM considers factors such as geology, pedology, geomorphology, water resources, and climate as represented by 13 associated environmental indicators. The results of the EISM indicate that more than 75% of California’s territory is situated in areas with very low, low, and medium environmental impact susceptibility categories. However, in the remaining 25% of the state’s land, 61 landfills are located in the high and very high categories. These results are alarming because during the period from 2000 to 2015, these 61 landfills received approximately 308 million tons of SW, which corresponds to more than 57% of all SW disposed in California. The model results can be used toward mitigating the environmental impacts of these facilities