[en] Gaseous nitrogen oxides (NO and NO₂) involved as oxidizing agents in nuclear fuel reprocessing can be produced by electrochemical reduction of nitric acid. This is an interesting alternative to the existing process because no wastes are generated. voltammetric studies on a platinum electrode show that two reduction potential regions are observed in concentrated nitric acid solutions, between 0,05 V_SHE and between 0,5 V_SHE and 1 V_SHE. The highest potential region reduction mechanism was studied by: classical micro-electrolysis methods, macro-electrolysis methods, infrared spectroscopy coupled to electrochemistry. It was determined that the origin of nitric acid reduction is the electrochemical reduction of nitrous acid in nitric oxide which chemically reduces nitric acid. This reaction produces nitrous acid back which indicate an auto-catalytic behaviour of nitric acid reduction mechanism. Nitrogen dioxide evolution during nitric reduction can also explained by an other chemical reaction. If the potential value of platinum electrode is above 0,8 V_SHE, products of the indirect nitric acid reduction are nitrous acid, nitrogen oxide and nitrogen dioxide. Below this value nitric oxide can be reduced in nitrous oxide. Thus the potential value is the most important parameter for the nitrogen oxides production selectivity. However, owing to the auto-catalytic character of the reduction mechanism, potential value can be controlled during intentiostatic industrial electrolysis. (author)

[en] The specific features displayed by data on heavy ion elastic and inelastic angular distributions are discussed, and their physical origin is pointed out from semi-classical calculations in counterpart ambiguities in the phenomenological description of the optical potential appear. Two nucleon transfer reactions induced by heavy ions successfully point out important contributions of a two-step process where the transfer is proceeding via target and residual nucleus inelastic excitation. At incident energies not too high above the Coulomb barrier, such process produces clear shape changes between different final state angular distributions. At higher incident energy, the angular distributions are forward peaked and display oscillations for both mechanisms. As for four-nucleon transfer reactions, the existing data suggest that the nucleons are well transferred into a Os relative

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[en] Safety factors are widely used in structural design. For composite material structures, however, the lack of experimental feed-back does not allow the use of safety factors optimized from cost and reliability point of view. Reliability methods are one way to achieve the calibration of partial safety factors using a more rational method than judgement alone. First we present the calibration process. The reliability methods FORM, SORM, simulation, are initially applied to a laminate plate under uniform pressure. In this example, we compare three design criteria; the different reliability methods agree with the reference method for all criteria used. We chose the Tsai-Hill criteria and the FORM method to calculate safety factors. Then, a calibration process is undertaken on a composite pipe and this serves to illustrate the different steps in the calculation. Finally, we present a calibration of a general plate structure. The partial safety factors and their sensitivities to the different parameters of the stochastic variables are given according to load type

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[en] In this paper, a formulation to compute the reliability of reinforced concrete structures, in which physical and geometrical non-linearities are taken into account, is described. The adopted non-linear model allows the representation of the mechanical behaviour of concrete structures at the failure stage, which is governed by possible large displacement effects, softening behaviour of concrete and tension stiffening effects. On the other hand, the reliability model is based on adaptive failure surfaces representing the mechanical model responses. The failure surface is obtained by fitting the internal force ultimate state of the structure using a quadratic polynomial. The structural reliability index is estimated by the Rackwitz and Fiessler algorithm, which has shown to converge after a reduced amount of iterations. A parametric numerical analysis of columns and frames is presented for practical applications, where the partial safety factors proposed by international codes of practice are associated with reliability indexes

[en] Time-variant reliability problems appear in the engineering practice when (a) the material properties of the structure deteriorate in time or (b) random loading modelled as random processes is involved. This paper presents a method called PHI2 which is based on the outcrossing approach and allows to solve such problems using classical time-invariant reliability tools such as FORM/SORM methods. The PHI2 method is first presented. Then it is benchmarked with the well-established 'asymptotic methods' [Stochast. Process. Appl. 13 (1988) 195; J. Offshore Mech. Arctic Engng 113 (1991) 241; Probab. Engng Mech. 10 (1995) 53; J. Struct. Engng 25 (1998) 1] on three examples dealing with scalar or vector processes and linear or non-linear limit state functions. The PHI2 method appears more accurate in all cases. As an application example, the method is finally applied on a case representing a mechanical system (a beam) placed in an environment that can have exceptional configuration

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[en] This paper presents a probabilistic methodology for nonlinear fracture analysis in order to get decisive help for the reparation and functioning optimization of general cracked structures. It involves nonlinear finite element analysis. Two methods are studied for the coupling of finite element with reliability software: the direct method and the quadratic response surface method. To ensure the response surface efficiency, we introduce new quality measures in the convergence scheme. An example of a cracked pipe is presented to illustrate the proposed methodology. The results show that the methodology is able to give accurate probabilistic characterization of the J-integral in elastic-plastic fracture mechanics without obvious time consumption. By introducing an 'analysis re-using' technique, we show how the response surface method becomes cost attractive in case of incremental finite element analysis

No abstract available