Influence de l'ecrouissage sur la formation des cavites d'irradiation dans l'aluminium

Aluminium samples, either annealed or in the asdeformed condition, were subjected to irradiation doses ranging from 8 × 10¹⁹ to 3.1 × 10²¹ n/cm². Initial deformation raises the degree of swelling associated with voids in aluminium irradiated at 55 °C, but reduces it at 220 °C. In annealed aluminium the loops are sometimes interstitial-type, sometimes vacancy-type; the appearance of voids is linked to an increase in the density of dislocations. Examination of samples stretched by different amounts shows that at a fixed temperature swelling is a function of the dislocation density introduced initially.     

Etude de la formation des cavites d'irradiation dans le cuivre II-irradiation aux ions cuivre de 500 keV — effet de la dose

The development of microstructure as a function of the irradiation dose has been studied for thick foils of copper irradiated by 500 keV copper ions. A comparison between the results obtained with degassed samples and those for non-degas-sed samples has allowed us to show that the gases dissolved in the metal aided the nucleation of interstitial loops. The relationships between the interstitial loops and voids were studied, and some conclusions drawn concerning the growth of voids and the effect of free surfaces.     

Etude de la formation des cavites d'irradiation dans le cuivre I-irradiation aux electrons de 1 MeV

We have studied the lormation of voids and interstitial loops in thin copper foils irradiated by 1 MeV electrons as a function of temperature and of gas content. We have observed a close relationship between voids and the dislocation network. By irradiating specimens degassed by annealing, we were able to show that for irradiation temperatures ? 100°C, it is the gas dissolved in the matrix which is responsible for nucleating both loops and voids. It follows that the upper temperature limit and the temperature of maximum swelling are displaced to higher temperatures when the gas content of the material increases. The temperature range of swelling and the position of peak swelling are therefore linked above all to the nucleation conditions of the defect accumulations.     

Etude de la formation des cavites dtrradiation dans le cuivre IV-etude des mecanismes

The analysis of experimental results concerning the formation of irradiation-voids in copper bombarded by electrons, by copper ions and by neutrons has been performed by means of a computer simulation model by the Monte Carlo method. The computations show that the nucleation of voids results from competition between the growth of vacancy aggregates formed in displacement spikes, the formation of vacancy aggregates by precipitation of mobile vacancies and the diffusion of gas towards vacancy aggregates already formed or in course of formation. Moreover, the theoretical curves representing the variation of swelling with temperature, for irradiation with electrons, ions and neutrons, are in excellent agreement with experimental results.     

Amelioration de la precision du dosage de l'oxygene dans le sodium par la methode d'amalgamation

The difficulties in analyzing oxygen present in trace amounts in liquid sodium by the amalgamation method stem from the possibility of contamination of sodium during the manipulations and transfers. The precision has been improved by developing a method of working which made it possible to estimate the contamination during each analysis. The results obtained are compared to the values obtained by the classical amalgamation method and also to those quoted by Noden, obtained by vacuum distillation or by use of the vanadium-wire and the electrolytic oxygen meter.     

Contribution a l'etude des cinetiques de l'oxydation a l'air du hafnium

The oxidation kinetics in air of Van Arkel hafnium were studied between 750 and 950°C. Comparison of the results obtained by thermogravimetry and microhardness measurements has allowed us to characterise the overall oxidation kinetics which are of parabolic type and also the two separate kinetics, likewise parabolic, of growth of the oxide film and of dissolution of oxygen in the metal underlying the oxide. For each of these three kinetics the rate constants are respectively given by the following relations: $\text{K}{}_{\mathrm{p}}\text{= 3.1 × 10}{}^8\text{exp (?46 000/RT)}$, $\text{K}{}_1\text{= 1.4 × 10}{}^6\text{exp (?36 000/RT)}$, $\text{K}{}_2\text{= 3.4 × 10}{}^{10}\text{exp (?59 000/RT)}$.These results are in agreement with a classical diffusion model of oxygen, both in the oxide and in the metal, set up on the basis of Wagner's general theory. The activation energy of diffusion of oxygen in hafnium is $\text{53.0 ± 2}$ kcal/mole.     

Influence des conditions de trempe sur le gonflement par irradiation aux neutrons d'un acier austenitique au niobium

Steels of type AISI 316 and 318 which had been subjected to different heat-treatments were neutron-irradiated at 450 °C to a fluence of 5 × 10²¹ n/cm². Density measurements after irradiation reveal a swelling of 0.15% for AISI 316 and 318 steels quenched from 1050 °C and tempered at 700 °C. A homogeneous dispersion of niobium carbide does not appear to influence the amount of swelling. On the other hand, the AISI 318 steel hyperquenched from 1270 °C and tempered at 700 °C swells to an extent of only 0.025%. Examination by electron microscopy showed that this reduction in swelling is associated with the dispersion of the fine niobium carbide precipitates on extrinsic stacking faults, as a consequence of the heat-treatment. It was noted that voids were absent in the neighbourhood of these stacking faults with their associated precipitates.     

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.     

Role de l'iode sur le developpement de la reaction entre le combustible et sa gaine in acier inoxydable (type 316) dans les reacteurs

During the operation of a reactor, the fuel $\text{(U, Pu}{}_{\mathrm{2-x}}\text{)}$ reacts with its cladding (stainless steel). The role of iodine, a fission product, in this reaction has been examined. Out-of-pile experiments have been done to study the compatibility of stainless steel with iodine, in open or closed systems, isothennally or in a temperature gradient, with or without the presence of fuel, using metallography, X-ray diffraction and X-ray microprobe analysis. Under isothermal conditions, iodine reacts directly with 316 stainless steel. Taking into account its composition and thermodynamie variables, iodides form in the following order:$\text{Mnl}{}_2\text{, Mnl}{}_2\text{+ Crl}{}_2\text{, Mnl}{}_2\text{+ Crl}{}_2\text{+ Fel}{}_2\text{, Mnl}{}_2\text{+ Crl}{}_2\text{+ Fel}{}_2\text{+ Nil}{}_2$In a thermal gradient, spectacular corrosion of the steel at low temperature is accompanied by substantial loss of chromium. In the hot zones, iron and chrome precipitate in equivalent amounts. The presence of $\text{(U, Pu)O}{}_{\mathrm{-x}}$in no way alters these observed phenomena. Thus the corrosive action of iodine on steel does not require the presence of oxygen. In irradiated fuel, free iodine (or iodine liberated by the decomposition of caesium iodide, a compound of fission products) can take part in the development of the reaction between fuel and cladding by demanding the latter of chromium, which reduces its resistance to oxidation by $\text{(U, Pu)O}{}_{\mathrm{2-x}}$.     

Evolution de la perméabilité des revêtements de pyrocarbone isotrope avec l'irradiation

The change in the gas permeability of isotiopic pyrocarbon during irradiation by fast neutrons was followed by gaseous flow measurements performed with ¹⁴C labelled carbon dioxide. After exposure of pyrocarbon to fluences of about 7 × 10²¹ n/cm², the almost complete disappearance of the permeability is observed, a phenomenon probably related to the contraction of a part of the microporosity (pores of radii which are smaller than 10 nm).     

Heterodiffusion de l'or,de l'argent et du cuivre dans les phases cubiques δ et ε du plutonium

The solute diffusion at infinite dilution of ¹⁹⁸Au and ^110mAg in cubic phases of Pu has been studied using the serial sectroning method. The solute diffusion coefficients in the b.c.c. ? phase can be expressed by: $\text{D}{}^{\mathrm{Au}}{}_{\mathrm{?Pu}}\text{= 5,7 × 10}{}^{\mathrm{?5}}$ exp(?10300/RT) cm²/s and $\text{D}{}^{\mathrm{Ag}}{}_{\mathrm{?Pu}}\text{= 4,9 × 10}{}^{\mathrm{?5}}\text{exp(?9600/RT) cm}{}^2\text{/s}$. The solute diffusion mechanism is interstitial of the dissociative type in both cases. These experiments confirm the activated interstitial model which has been proposed for self diffusion of ?Pu. Indeed the solute diffusion coefficients of Au and Ag are near of the self diffusion coefficients of Pu. The mechanisms are therefore interstitial in both cases. In the f.c.c. δ phase of Pu where self diffusion takes place by a vacancy mechanism, the solute diffusion coefficients of Au and Ag are near of the self diffusion coefficients of δ Pu. Solute diffusion takes place also by a vacancy mechanism. On the other hand, the extrapolation at infinite dilution of experiments of solute diffusion of Cu in ?Pu (Matano-Wagner coupling) gives the following results: $\text{D}{}^{\mathrm{Cu}}{}_{\mathrm{?Pu}}\text{= 1 × 10}{}^{\mathrm{?3}}\text{exp(?12300/RT)}$ cm²/s. The solute diffusion mechanism is interstitial of the dissociative type. In the ? phase the smaller the atomic radius the faster the migration: r_Co < r_Cu < r_?Pu < r_Ag = r_Au, and D^Co_?Pu > D^Cu_?Pu >D^Pu_?PU > D^Ag_?Pu ≈ D^Au_?Pu.     

Etude de la reaction du magnesium massif avec l'air

The reaction of magnesium with air follows very irregular kinetics; periods of slow and rapid growth alternate in random fashion. We show that initially the metal reacts simultaneously with nitrogen and oxygen. A nitride layer is formed next to the metal and an oxide layer next to the gas. This double layer becomes temporarily protective, which leads to a substantial slowing down of the rate of weight increase. Sudden cracking entails a rapid acceleration of both oxydation and nitridation, giving rise to two surface layers. An irregular sequence of several fast and slow stages leads to the development of a sharply layered film. The cracks formed when the oxide layer is thicker are gradually sealed by the products of vapour-phase reactions. The total layer then acquires a distinct protective power, and the gases can no longer reach the metal surface. The reaction then starts again by the oxidation of the strata of nitride formed earlier and proceeds at a slow but regular pace.     

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.