[en] A number of creep tests both in vacuum and in dynamic sodium were made which allowed the determination of the influence of a well qualified sodium on secondary creep rate, time-to-rupture and fracture mechanism. Results are correlated to chemical and metallurgical changes appearing in the steel during sodium exposure. Conclusions are formulated and the composition of surface layer as a function of exposure time in sodium is shown in a table for elements Fe, Ni, Cr, Mn, Mo, and Si

No abstract available

[en] The chemistry of carbon in sodium is described by its chemical activity measurements using alloy monitor foils, by its behaviour in the heat exchanger of the Na 2 sodium loop after 60,000 hours of operation, and by measurements with on-line meters. Efforts toward the identification of the carbon chemical states present in dynamic sodium, and responsible for the carbon chemical activity, are described. (author)

[en] A study of dissolved non-metals such as carbon, nitrogen, oxygen and hydrogen in liquid alkali metals is presented. Activity-concentration relationships are deduced from ''terminal'' solubility equations for N, C, O and N in liquid lithium and sodium. Related thermodynamic quantities such as partial molar entropies and enthalpies are deduced and indicate a similar solvation pattern for these non-metals in lithium as compared to sodium, although considerable differences in bond energy exist for C, H, O and N in liquid Na as compared to Li

[en] Uniaxial creep tests on X8CrNiMo V Nb 1613 (DIN 1.4988) and X10NiCrMoTiB 1515 (DIN 1.4970) tubes have been carried out at 700⁰C both in dynamic sodium and in vacuum at different stress levels in order to establish the influence of a well-defined sodium quality on the secondary creep rate, the onset of tertiary creep, the time-to-rupture, and the fracture mechanism for these stabilized austenitic steels. Mechanisms which can be responsible for changes of creep properties are diffusion-controlled processes such as preferential leaching of substitutional elements and loss or pick-up of interstitial elements; furthermore, physico-chemical processes such as general corrosion, grain boundary grooving, surface pitting and crack promoting processes. The observed structural and chemical changes have been evaluated and cannot be responsible for variations of the creep parameters. The dynamic sodium environment promotes intergranular cracking in the DIN 1.4988 steel, whereas in the DIN 1.4970 steel rapid local corrosion in deformation bands causes the growth of an irregular branched fracture path from the sodium exposed surface. However, the main creep parameters of both steels are not significantly influenced by the presence of flowing sodium

[en] The analysis of the corrosive products present in an air stream passing over clay revealed that at higher temperatures S and S-compounds are the main products governing the corrosiveness of the atmosphere in holes of a geological clay formation. The presence of SO₂ in the moisture and gases escaping from the clay is mainly due to the presence of pyrite in the clay and the chemical reaction induced in the clay with pyrite and humidity. Exposure of aluminum and its alloys to the acid environment results in rapid uniform attack and pit formation induced by S^- and Cl^- compounds. The corrosion resistance of steels in the acid S and Cl^- containing environment is in accordance with literature data. Carbon steel had large corrosion rates in acid environments; the quality of a Cr coating is insufficient to protect the non-noble underlying carbon steel. The results obtained for the austenitic grades are in agreement with published corrosion data in acid SO₂, Cl^- and H₂SO₄ containing environments. Higher molybdenum contents and lower interstitial contents result in enhanced corrosion resistance. Sulphur, and to a lesser extent Cl^-, determine the corrosion mechanism of the austenitic and ferritic grades. The result obtained for nickel and superalloys can be explained by the positive influence of higher Cr and Mo contents on general and localized attack by S compounds in the presence of Cl^- ions. The results obtained for Ti and its alloys are in agreement with the excellent behavior observed in different chemical environments. Salts and salt deposits played a dominant role in the corrosion mechanism of all tested material, since the hygroscopy of the salts keeps the aggressive environment in contact with the tested alloys even during the heating period of the corrosion chamber

[en] The corrosion rate and mechanism of construction materials of galleries and casings for boreholes (possibly to be used as consumable overpack of HLW canisters) have been evaluated after a first campaign of corrosion experiments in direct contact with clay, in a humid clay atmosphere and in a gas corrosion chamber. The envisaged construction matrial is ductile iron (grade 60) and has been tested with and without metallic and organic coatings. The corrosion mechanism is governed by the formation of a rust scale composed of Fe³O⁴ and C. Preferential attack underneath the surface reaction layer is associated with the progress of a reaction front at the interface between the graphic nodules or flakes and the ferritic or pearlitic structure. Post-corrosion analyses of old gray iron coal mine shafts exposed for 60 and 90 years in well defined conditions are included to validate the use of the results of the short-time tests for very long exposure times. 3 figures, 10 tables

No abstract available

[en] Detailed post-corrosion analyses of an AISI 316L sodium-sodium heat exchanger after 60,000 hours of operation between 680⁰C and 240⁰C have been performed. Temperature regions characterized by selective corrosion and by deposition phenomena both in up- and downstream positions have been delineated. Interaction between deposits and substrate takes place by a grain boundary mechanism. The distribution of carbon and nitrogen in the deposits and their subsequent penetration in the base material have been determined and compared with theoretical models

[en] Thin foils of Fe 8 wt.% Ni, Fe 20 wt.% Ni, Fe 30 wt.% Ni, Fe 12 wt.% Mn, Fe 20 wt.% Mn and AISI 304 (DEW 202 and DEW 201) were exposed to sodium in the temperature range between 730/degree/C and 550/degree/C. Carbon activity is influenced by the temperature of the cold trap. The nitrogen activity is one order of magnitude smaller. Austenitic and ferritic steels react in different ways during exposure. 20 refs