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The prediction of long-term behaviour of reinforced concrete structures involved in the nuclear industry requires a phenomenological modelling of the rebars corrosion processes. Previous analytical characterisation of archaeological artefacts allowed to identify a typical layout constituted of four layers (the metal, the dense product layer, the transformed medium and the binder). Additional experiments leaded to identify the long-term corrosion mechanisms. Following these results, this paper proposes an analytical model of long-term corrosion of rebars embedded in concrete. This modelling is considering the kinetic of oxygen diffusion through the system and its consumption at the metal/dense product layer interface as a function of concrete water saturation degree. Corrosion products thicknesses estimated with the model are then compared to corrosion product thicknesses measured on archaeological artefacts. A parametric study is performed and demonstrates that the oxygen diffusivity and the kinetic constant of the cathodic reaction affect in a wide range the model results.

The prediction of long-term behaviour of reinforced concrete structures involved in the nuclear industry requires the comprehension of the mechanism involved in long-term corrosion. Yet, studies on archeological artefacts allowed to identify a typical layout constituted of four layers: the metal, the dense product layer (DPL), the transformed medium (TM) and the binder. Oxygen reaction sites were labelled using oxygen 18 ( 18 O) and it was evidenced that the cathodic sites are located at the metal/dense product layer interface. So, oxygen has to crossed the DPL to react at the M/DPL interface or inside the marblings, and measurements of the effective tritiated water (2.6 ± 0.1 × 10 −11 m 2 /s) and iodide (1.0 ± 0.3 × 10 −11 m 2 /s) diffusivity of this layer saturated with water were made. Indeed, these two molecules have a diffusivity in water very closed to oxygen diffusivity.

Because “safety” is still the key point in the Nuclear industry, more than in any others, the use of new materials or new manufacturing methods is really challenging. Among many characterizations required for a new steel grade or a new manufacturing process to be accepted and then introduced in a Nuclear design code, the fatigue properties must be determined with great care. Nowadays, the consideration of the Pressurized Water Reactor (PWR) primary water environment effect on the Low Cycle Fatigue (LCF) behavior of Austenitic Stainless Steels (ASS’s) is an important issue for both Nuclear Power Plants (NPP) lifetime extensions and new builds as described in the NUREG/CR-6909 [1], [2]. This paper aims to present the LCF behaviors in air and in PWR water at 300°C of type 304L and 316L ASS’s manufactured by Powder Metallurgy coupled with Hot Isostatic Pressing process (PM/HIP) and to compare them with those observed on usual ASS nuclear grade products [3]-[6]. As already introduced in our previous paper [7] dedicated only to the PM/HIP 304L steel fatigue behavior, it appears that the microstructures, mechanical properties and LCF behaviors in air and in PWR water of both type 304L and 316L steels manufactured by PM/HIP process are better or at least similar to those observed on wrought ASS’s.

Because “safety” is still the key point in the Nuclear industry, more than in any others, the use of new materials or new manufacturing methods is really challenging. Among many characterizations required for a new steel grade or a new manufacturing process to be accepted and then introduced in a Nuclear design code, the fatigue properties must be determined with great care.Nowadays, the consideration of the Pressurized Water Reactor (PWR) primary water environment effect on the Low Cycle Fatigue (LCF) behavior of Austenitic Stainless Steels (ASS’s) is an important issue for both Nuclear Power Plants (NPP) lifetime extensions and new builds as described in the NUREG/CR-6909 [1], [2].This paper aims to present the LCF behaviors in air and in PWR water at 300°C of type 304L and 316L ASS’s manufactured by Powder Metallurgy coupled with Hot Isostatic Pressing process (PM/HIP) and to compare them with those observed on usual ASS nuclear grade products [3]-[6].As already introduced in our previous paper [7] dedicated only to the PM/HIP 304L steel fatigue behavior, it appears that the microstructures, mechanical properties and LCF behaviors in air and in PWR water of both type 304L and 316L steels manufactured by PM/HIP process are better or at least similar to those observed on wrought ASS’s.Copyright © 2015 by ASME

In a pressurized water reactor components are affected by relative motions. Typically, components and associated supports are excited by a range of configurations such as sliding, fretting and impact. Thus wear of components can occur. Most of the materials are passivating alloys working in a relatively aggressive environment: high temperatures, pressure, boric acid and lithium hydroxide. This peculiar environment and the motions highlighted previously are favorable to tribocorrosion mechanisms. AREVANP studies such mechanisms because wear phenomena that affect nuclear components threaten efficiency and service lives and could raise nuclear safety issues. The methodology and specific tribometers developed in order to understand the influence of mechanical parameters and of this specific environment are described.

The study of archaeological analogues is necessary to improve the knowledge on the long-term corrosion of low carbon steels that could be used in concrete to build the structures of nuclear waste storage facilities. The long-term corrosion system was previously described as a multi-layer pattern made of the Metal, the Dense Product Layer (constituted of goethite with magnetite and/or maghemite marblings -DPL), the Transformed Medium (TM) which is an interphase between the Dense Product Layer, and the last layer, the Binder. As mainly constituted of goethite, a non-conductive phase, and assuming that the DPL pores are saturated with water, corrosion kinetic could be limited by oxygen diffusion in the water of the pores. Moreover, anodic and cathodic reactions should occur at the Metal/DPL interface. This last hypothesis was verified labelling oxygen precipitation sites with an oxygen isotope ( 18 O) and observing an increase of oxygen isotopic ratio at the M/DPL interface. Then, to validate the hypothesis of a diffusion control of corrosion kinetic, some investigations were performed on diffusion properties of oxygen in the DPL. For this purpose, the oxygen apparent diffusion coefficient was evaluated using diffusion cells made with DPL sampled on archaeological analogues. Then, thanks to Faraday law, it was possible to evaluate instantaneous corrosion rates (less than 0.1 μm/year). The compatibility of these rates with those obtained considering the quantity of 18 O precipitated in corrosion products was discussed. Nevertheless, even if oxygen diffusion is probably the limiting factor on iron corrosion in the very specific case of water saturated media, the hydrometry of the DPL during the life time of the object and the influence of this hydrometry on corrosion mechanisms have to be verified. Moreover, several questions were raised by TM formation and growth. Was this layer formed dissolving/precipitating corrosion products from the DPL? Unfortunately, thermodynamical data and results from our experimentation show that iron quantity obtained by this mean is not sufficient to explain TM thicknesses observed and, so far, TM formation mechanisms are still to be identified.

The tribocorrosion of a Stellite 21 type alloy sliding against alumina in sulfuric acid was investigated in order to identify relevant degradation mechanisms. Tribocorrosion tests were performed using a reciprocating motion pin-on-plate system operating under potentiostatic conditions as well as open circuit potential under different loadings. Scanning electron microscopy, optical microscopy, laser profilometry and focus ion beam (FIB) were used for characterizing wear pattern and subsurface deformation. Results show that the prevailing electrochemical conditions, and in particular the presence or not of a passive film, crucially affect the tribocorrosion behavior of this alloy. The passive film was found to significantly enhance tribocorrosion damage and this for two reasons: (i) abrasion of the passive film induces wear accelerated corrosion, (ii) the presence of the passive film significantly increases subsurface deformation in the metal and thus mechanical wear. The effect of electrode potential and normal load on the overall degradation by tribocorrosion could be accurately described by the Archard's wear law (taking into consideration the effect of the passive film) and existing models for wear accelerated corrosion. (C) 2013 Elsevier B.V. All rights reserved

Existing sliding tribocorrosion models have been developed for homogeneous passive metals such as stainless steel and pure metals. Many technical alloys contains however second phases, usually much harder than the metallic matrix, intended to provide better mechanical properties. The tribocorrosion models are based on the assumption of nearly perfect plastic behavior that is not necessarily representative of the tribological response of inhomogeneous metals. This work was initiated with the aim of evaluating the applicability to inhomogeneous alloys of a recently developed tribocorrosion model that includes mechanical, chemical and lubrication phenomena. For this the tribocorrosion of three different CoCr alloys was investigated using a reciprocating ball (alumina)-on-plate tribometer in a 0.5 M sulfuric acid solution. The alloys studied were a Stellite 6 (S6) with 22% of carbides, a Stellite 21 (S21) with 6% of carbides and a Stellite 21 (LCS21) without carbides. Tribocorrosion tests were carried out under potentiostatic conditions under different loads. Scanning electron microscopy, laser profilometry and focused ion beam were used for surface and sub-surface characterization of the wear tracks. The results obtained with the S21 and LCS21 alloys are consistent with the model while in the case of alloy S6, exhibiting interconnected carbide phases, the model correctly describes the corrosion response but only approximately the mechanical release of wear particles. (C) 2017 Elsevier B.V. All rights reserved.

The tribocorrosion behaviour of a 304L stainless steel/alumina contact was investigated in sulphuric acid at two imposed potentials (cathodic and passive) The metal deformation below the surface was investigated by analyzing cross sections using secondary electron microscopy (SEM) and electron back scatter diffraction (EBSD) Cross sections were also prepared using focussed ion beam (FIB) and analyzed by in situ SEM. AES depth profiling was used to analyze surface composition Metal subsurface deformation resulted in the build up of a deformed layer of approximately 20 mu m thickness in the near surface zone within the wear track This layer exhibited a deformation gradient with high deformation close to the surface resulting in grain refinement down to 10 nm The applied potential influenced the deformation at passive applied potential more strain was accumulated below the surface resulting in more pronounced grain refinement and higher density of defects. Using AES analysis no alumina transfer from the counter body or any significant burying of oxide below the surface could be detected (C) 2010 Elsevier B.V All rights reserved.