Determination des parametres d'irradiation de materiaux de structure en piles

Problems of neutronic parameters for radiation damage experiments are briefly reviewed. These are the problems of fluence, flux level (or irradiation time) and temperature. In particular the GAMIN graphite detector, which measures ‘graphite flux’ and $\text{r}$ spectrum indices (graphite/nickel), is described. The results of an international set of $\text{r}$ indices are summarized.     

Etude des transformations de phase dans les alliages uranium-vanadium. Influence de la teneur en carbone

This work completes the study of the refinement of the U-V alloys with a low V content (from 0.1 to 1%). The kinetics of the U_β → U_α transformation which determines the size of the α grains are in particular most sensitive to the carbon content. Microdiffraction analysis of the precipitates formed upon cooling these alloys gives evidence of a V-C type of interaction in the solid phase, the characteristics of which are given. The transformation curves, which were obtained for different V and C contents, show that the latter element cannot only deflate the β matrix in V through the formation of carbides of composition V₂C or with an intermediate formula between V₂C and VC but can also act on the intrinsic stability of the (U, V)_β solution.     

Production de defauts dans des films de fer; etude en fonction de la densite d'energie deposee dans les cascades

Oxidation of SUS-316 stainless steel for a fast breeder reactor fuel cladding was examined in the temperature range of 843–1010 K under the oxygen pressure of 1017 t – 10 t-13 Pa hy use of an experimental technique of a Ni/NiO oxygen buffer. The formation of the duplex oxide layer, i.e. an outer Fe₃O₄ layer and an inner (Fe, Cr, Ni)-spinel layer, was observed and the oxidation kinetics was found to obey the parabolic rate law. The oxygen pressure and temperature dependence of the parabolic rate constant k_p(P_O2,T) was determined as follows: k_p(P_O2,T)/kg² · m^?1 · s^?1 = 0.170(P_O2/Pa)^0.141exp[?114 × 10³/(RT/J)]. On the basis of the oxidation kinetics and the metallographic information, the outward diffusion of Fe in the outer oxide layer was assigned to be the rate-determining process.     

Etude de l'alliage mulberry [U-7,5 Nb-2,5 Zr (% ponderaux)]. diagramme de transformation en refroidissement continu-structures et proprietes mecaniques

We have studied by dilatometry, microscopy, X-ray and electron diffraction, the phase transformations generated by controlled cooling from 900° C of the “Mulberry” alloy (U-7.5 wt%Zr). For slow cooling rates, three types of decomposition of the 7 phase appear successively: (i) Between 600°C and 550°C, grain boundaries and inclusion serve as nucleation sites for a cellular reaction, $\text{γ→α+γ}$; (ii) between 550°C and 400°C, a continuous transformation of the matrix generates an a phase in the form of Widmanstätten plates, and (iii) below 400°C, the γ phase gives rise to an α″ phase which has an ultrafine structure only imperfectly resolved by TEM. On rapid cooling, a tetragonal phase, γ₀, appears. Quenching generates the γ_S phase derived from γ, with a structure crystallizing in 143m which has been described by YakeL The various methods of investigation used have allowed us to obtain heating and cooling curves of the alloy and thus to determine phase fields. In general terms, the structures formed are similar to those obtained by isothermal annealing below 600° C. Only the γ_S phase has useful mechanical properties, notably good ductibility. The other phases are characterised by extreme brittleness.     

Considerations sur la relation entre le fluage sous irradiation et les dommages crees par l'irradiation en l'absence de contrainte

The migration to dislocations of vacancies or interstitials created during neutron-irradiation brings about supplementary creep when one type of point defect is segregated in loops or voids. A balance-sheet of defects arriving at dislocations is set up, not by solving the diffusion equations but rather by taking account of the experimentally observed growth of interstitial loops and of voids in irradiated samples.     

Les travaux du sous-groupe ‘dommages d'irradiation’ du groupe de travail d'EURATOM sur la dosimétrie en réacteur de recherche

The EURATOM Working Group on Reactor Dosimetry is investigating the problems of the dosimetry of radiation damage experiments. Papers have been published on the dosimetry of graphite and irradiation of metals: the model chosen, the quantities employed to express the fluences, numerical values, measurements and measurement techniques. The ensuing work of the EURATOM Working Group on Reactor Dosimetry in these areas will deal with the measurement methods required for the dosimetry of radiation damage.     

Elaboration de monocristaux de zirconium α et etude de leur perfection cristalline

The methods depending on critical straining followed by α-phase annealing, or on thermal cycling across the allotropie transformation temperature, do not enable the production of large zirconium crystals of predetermined orientation. A method based on localised phase transformation in a controlled thermal gradient has been successfully developed: it permits the preparation of crystals up to 100 mm long in favourable cases. A study of the mechanism of formation of an α monocrystal from a β monocrystal has led to a recognition of the parameters which determine the growth of the desired monocrystals. An analysis of the crystal orientations obtained has established the optimal conditions for obtaining orientations close to a desired one. X-ray methods have been used to examine the perfection of the crystals: some were strongly polygonised but others had overall misorientations of less than 10^?2 degree.     

Dilatation thermique d'oxydes mixtes (UPu)O2−x en fonction de l'ecart a la stoechiometrie

The thermal expansion of mixed oxides (UPu)O_2?x has been measured between 25 and 1300°C using differential dilatometer. It is concluded that expansion coefficient increases with the deviation from stoichiometry.