[en] Austenitic stainless steels can suffer intergranular corrosion (IGC) in nitric acid even though they have a low carbon content and they are not sensitized (by welding, for example). Under high oxidizing conditions (high temperature, high nitric acid concentration and with the presence of other oxidizing species) the corrosion potential of stainless steels is increased to the trans-passive zone. In this domain the grain boundaries are preferentially attacked. Grooves are formed between the grain and their progression leads to grains drops. Because IGC is of heterogeneous nature the calculation of the steel degradation kinetics is not easy. For this particular form of IGC a model is proposed to estimate the life duration of these materials. The IGC is described with two different corrosion rates: Vj, the local corrosion rate at the grain boundaries, and Vs, the corrosion rate on the grain surface. Vs and Vj are bounded with the morphology of the grooves (angle and deepness). Supposing that Vj and Vs are not time-dependent the model reproduces the evolution of the IGC morphology and of some parameters such as the thickness affected by the IGC, the mass loss (expressed in terms of equivalent homogeneous thickness loss) and the relative surface in contact with the corrosive medium. The methodology is as follows. The corrosion rates Vj and Vs are estimated with a short corrosion test by characterizing the groove morphology. Then the model can extrapolate the long-term behavior of the IGC. The calculations of the model were successfully compared to some long-term corrosion experiments. (authors)

[en] Within the context of long-lived intermediate level radioactive waste geological disposal, reinforced concrete would be used. In service life conditions, the concrete structures would be subjected to drying and carbonation. Carbonation relates to the reaction between carbon dioxide (CO₂) and the main hydrates of the cement paste (portlandite and C-S-H). Beyond the fall of the pore solution pH, indicative of steel depassivation, carbonation induces mineralogical and microstructural changes (due to portlandite and C-S-H dissolution and calcium carbonate precipitation). This results in the modification of the transport properties, which can impact the structure durability. Because concrete durability depends on water transport, this study focuses on the influence of carbonation on water transport properties. In fact, the transport properties of sound materials are known but they still remain to be assessed for carbonated ones. An experimental program has been designed to investigate the transport properties in carbonated materials. Four hardened cement pastes, differing in mineralogy, are carbonated in an accelerated carbonation device (in controlled environmental conditions) at CO₂ partial pressure of about 3%. Once fully carbonated, all the data needed to describe water transport, using a simplified approach, will be evaluated. (authors)

[en] Some ferritic/martensitic oxide dispersed strengthened (F/M ODS) steels are presently developed at CEA for the fuel cladding of the next generation of sodium fast nuclear reactors. The objective of this work is to study if this change of cladding could have any consequences on the spent fuel reprocessing PUREX process. During the fuel dissolution stage the cladding can actually be corroded by nitric acid. But some process specifications impose not to exceed a limit concentration of the corrosion products such as iron and chromium in the dissolution medium. For that purpose the corrosion behavior of these F/M ODS steels is studied in hot and concentrated nitric acid. The influence of some metallurgical parameters such as the chromium content, the elaboration process and the presence of the yttrium oxides is first discussed. The influence of environmental parameters such as the nitric acid concentration, the temperature and the presence of oxidizing species coming from the fuel is then analyzed. The corrosion rate is characterized by mass loss measurements and electrochemical tests. Analyses of the corroded surface are carried out by X-ray photoelectron spectroscopy.

[en] This paper studies the corrosion behaviour of non-sensitized stainless steels in oxidizing environments, where they can suffer intergranular corrosion. In this case, corrosion rate estimated by gravimetric measurement is not constant as a function of time. This paper proposes a quantitative modelling of the IGC kinetics. Two models were developed: the first one is based on the geometrical simulation of the groove penetration; the second one uses a semi-empirical approach based on the typical shape of the corrosion kinetics. Both models reproduce successfully the experimental corrosion kinetics observed for a AISI 310L stainless steel corroded in nitric acid containing oxidizing ions. (authors)

[en] Cement-based materials would be commonly used for nuclear waste management and, particularly for geological disposal vaults as well as containers in France. Under service conditions, the structures would be subjected to simultaneous drying and carbonation. Carbonation relates to the reaction between CO₂ and the hydrated cement phases (mainly portlandite and C-S-H). It induces mineralogical and microstructural changes (due to hydrates dissolution and calcium carbonate precipitation). It results in transport properties modifications, which can have important consequences on the durability of reinforced concrete structures. Concrete durability is greatly influenced by water: water is necessary for chemical reactions to occur and significantly impacts transport. The evaluation of the unsaturated water transport properties in carbonated materials is then an important issue. That is the aim of this study. A program has been established to assess the water transport properties in carbonated materials. In this context, four mature hardened cement pastes (CEM I, CEM III/A, CEM V/A according to European standards and a Low-pH blend) are carbonated. Accelerated carbonation tests are performed in a specific device, controlling environmental conditions: (i) CO₂ content of 3%, to ensure representativeness of the mineralogical evolution compared to natural carbonation and (ii) 25 C. degrees and 55% RH, to optimize carbonation rate. After carbonation, the data needed to describe water transport are evaluated in the framework of simplified approach. Three physical parameters are required: (1) the concrete porosity, (2) the water retention curve and, (3) the effective permeability. The obtained results allow creating link between water transport properties of non-carbonated materials to carbonated ones. They also provide a better understanding of the effect of carbonation on water transport in cementitious materials and thus, complement literature data. (authors)