Browsing by Author "Insausti, Mikel"
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Item Corrosion behaviour of container candidate materials for HLW disposal in granite-bentonite media(2005-09) Madina, Virginia; Insausti, Mikel; Azkarate, Iñaki; Garmendia, Iñaki; Cuñado, Miguel A.; MATERIALES PARA CONDICIONES EXTREMAS; Tecnalia Research & InnovationAn extensive laboratory program is being carried out in order to evaluate the corrosion behavior of candidate container materials for the deep geological disposal of High Level Waste (HLW)(1-5). According to the Spanish multi-barrier concept for granite site, in which canisters are surrounded by compacted bentonite blocks, the corrosion behavior of various proposed container materials in saturated bentonite with granite water has been assessed. The studied materials have been S355 carbon steel, AISI 316L stainless steel, electrolytic copper and Cu30Ni alloy. Specimens from these alloys have been placed in saturated bentonite and tested at different temperatures and times. General corrosion rates and penetration data based on metallographic examinations have been obtained together with the analysis of the corrosion products generated during the test. S355 carbon steel shows the higher general corrosion attack, with average corrosion rates of 10 μm per year when tested at 100 °C. The main corrosion product for carbon steel has been siderite, FeCO3. At 25 and 50 °C, corrosion products with a high sulfur content are observed, thus indicating a microbiologically corrosion phenomena due to bacteria present in the bentonite. No corrosion attack has been observed in AISI 316L stainless steel samples. Good corrosion resistance have been shown by cooper and Cu30Ni, with general corrosion rates below 1 μm/year after being tested at 100 °C for 18 months.Item Corrosion of several components of the "in-situ" test performed in a deep geological granite disposal site(2004) Madina, Virginia; Azkarate, Iñaki; Insausti, Mikel; MATERIALES PARA CONDICIONES EXTREMAS; Tecnalia Research & InnovationThe corrosion damage experienced by different components in a deep geological disposal in a granite formation has been analysed. This "in-situ" test is part of the Full-scale Engineered Barriers EXperiment project (FEBEX) carried out in Grimsel (Switzerland). Two heaters, simulating the canister and the heat generated, were installed horizontally inside the guide tubes or liners and surrounded by highly compacted bentonite blocks. Coupons of several candidate metals for manufacturing HLW containers were introduced in these bentonite blocks, as well as sensors in order to monitor different physicochemical parameters during the test. The "in- situ" test began in July 1996 and in June 2002 one of the heaters, a section of the liner, several corrosion coupons and four sensors were extracted. The studied heater is a carbon steel cylinder with welded lids, with a wall thickness of 100 mm and 4.54 m long. The liner consists of a perforated carbon steel tube, 970 mm in diameter and 15 mm thick. Corrosion coupons were made of carbon steel, stainless steel, titanium, copper and cupro-nickel alloys. Two extensometer type sensors with an outer protection tube made of austenitic stainless steel were also analysed. Visual inspection of the above mentioned components, optical and scanning electron microscope study, together with EDS and XRD analyses of corrosion products, have been performed in order to analyse the corrosion suffered by these components. This has been complemented with the chemical and microbiological characterisation of bentonite samples. Results obtained in the study indicate a slight generalised corrosion for the heater, liner and corrosion coupons. The low humidity content of the bentonite surrounding the liner and the corrosion coupons, is the responsible of this practical absence of corrosion. The sensors studied show, however, an important corrosion damage. The sulphur rich corrosion products, the presence of Sulphate Reducing Bacteria (SRB) in the bentonite covering the sensors, as well as the morphology of the damage, indicate a corrosion phenomena induced by bacteria. This factor, together with the high humidity of the bentonite blocks housing the sensors, are responsible for the significant corrosion damage observed in these components.