[en] The behaviour of silicon carbide under irradiation has been studied using classical and ab initio simulations, focusing on the nano scale elementary processes. First, we have been interested in the calculation of threshold displacement energies, which are difficult to determine both experimentally and theoretically, and also the associated Frenkel pairs. In the framework of this thesis, we have carried out simulations in classical and ab initio molecular dynamics. For the classical approach, two types of potentials have been used: the Tersoff potential, which led to non satisfactory results, and a new one which has been developed during this thesis. This potential allows a better modelling of SiC under irradiation than most of the empirical potentials available for SiC. It is based on the EDIP potential, initially developed to describe defects in silicon, that we have generalized to SiC. For the ab initio approach, the feasibility of the calculations has been validated and average energies of 19 eV for the C and 38 eV for the Si sublattices have been determined, close to the values empirically used in the fusion community. The results obtained with the new potential EDIP are globally in agreement with those values. Finally, the elementary processes involved in the crystal recovery have been studied by calculating the stability of the created Frenkel pairs and determining possible recombination mechanisms with the nudged elastic band method. (author)

[en] An experimental program investigated the effects of texture anisotropy and irradiation on the mechanical behavior of Zircaloy-2. Short time and time dependent mechanical behavior were considered. Irradiation effects were simulated through the use of 4.75 MeV protons. The temperature ranges investigated were 298⁰K and 573 to 673⁰K. Both cold worked-stress relieved and annealed material were used in this experimental program. Short time yield behavior of different crystallographic textures was determined by uniaxial and plane strain tests in the temperature range 298⁰K and 573 to 673⁰K. Monotonic flow loci were constructed for each texture. Yield behavior is a strong function of the crystallographic texture number f at all temperatures investigated. The rotation of texture with increasing plastic strain was investigated as a function of initial texture at 298⁰K and 623⁰K. The rate of texture rotation df/epsilon/sub p/ was found to be a unique function of the initial texture for plastic strains less than 0.08. Time dependent mechanical behavior was investigated in the range 573 to 673⁰K using constant load creep and stress relaxation tests. The tensile creep strength is proportional to the resolved fraction of basal poles in the test direction. In variable stress and temperature tests, the time-hardening rule was found to be inapplicable. The strain-hardening rule was applied with success to data obtained at temperatures less than or equal to 648⁰K. Irradiation creep tests were conducted in vacuum at 598⁰K and 102 to 241 MPa on 80μm thick Zircaloy-2 foil specimens in both the recrystallized and cold worked-stress relieved condition. In the irradiation creep tests irradiation hardening and enhanced irradiation creep were observed. Radiation hardening effects were significant in annealed material but were attenuated in cold worked-stress relieved material

[en] The spectra of gamma radiation produced by the interaction of 1 MeV to 10 MeV neutrons on aluminum, iron and bismuth, for a diffusion angle of 90 deg., are presented. The 18 MeV electron linear accelerator delivers pulses of 3.5 ns. At each neutron energy interval determined by flight time, the corresponding gamma spectrum is recorded. The bi-parametric acquisition (En x E γ) is realized in 'line' with a C.I.I. 10020 calculator. The production cross sections of the gamma lines present in the return spectra are evaluated. Results are compared with previous results and commented

[en] This paper reports on a simulator which is a device which simulates a physical object for training purposes. Although effective tools, Simulators posses two primary limitations. First, due to the dynamic nature of the simulated object, the Simulator may require frequent modification to remain an accurate representation. When Simulators are upgraded, modifications often turn out to be expensive. Increasingly, Simulator upgrades are required by regulations, no matter how costly. The second limitation is the number of personnel that can utilize a Simulator simultaneously. Engineers, Instructors, and Students are frequently forced work second and third shifts to obtain Simulator time. A study of existing Simulators by the Power Plant Simulation Division of Link-Miles Corporation spawned a software development project. The purpose of this project was to minimize the limitations of existing Simulators by designing a system to enhance Simulator modifications and usage

[en] Abstract only

[en] The use of nuclear spectrometry technics with a precise measurement of monochromatic X rays fluxes allows a sensitive study of specific gravity variations. This method is perfectly applying to agregated, porous and composite materials. Measurement sensitivity is better than 2 per mille in relative value

[en] The development and verification of fracture criteria - including catastrophic failure and lead-before-break phenomena - are important to the assessment of fusion reactor structural integrity. Reliable assessments require appropriate measures to characterize the initiation, stable growth, and instability of part-through surface cracks in thin-walled structures. Consequently, we are developing electropotential drop techniques for monitoring the evolution of part-through cracks. Electropotential drop techniques are based on the proportionality between the potential required to drive a fixed current through a flaw. While the technique is well established for monitoring crack length in through-crack specimens, there has been less experience in using it to monitor part-through surface cracks where both crack size and shape must be monitored during loading. We have developed a technique to accomplish this using multiple probes across the crack mouth

[en] Leaching, the movement of water and chemicals into deeper soil layers and groundwater is a subject of worldwide interest because a high percentage of drinking water is extracted from groundwater. The objective of this study was to evaluate the potential leaching and persistence of sixteen pesticides (one fungicide, three nematicides/insecticides, and twelve herbicides) for three Mediterranean agricultural soils with similar texture (clay loam) but different organic matter content (1.2-3.1%). Adsorption was studied in batch experiments and leaching was tested using disturbed soil columns (40 cm length × 4 cm i.d.). Degradation studies were carried out during 120 days under laboratory conditions. Mobility experiments showed that pesticides can be grouped according to their potential leaching. Thus, pesticides showing medium leachability were included in group 1 (referred as G1) while those with high leachability were termed as G2. The differences observed in the leachability can be attributed to the different organic carbon (OC) content in the soils (0.7-1.8%). Values of log KOC were higher in the order: soil C > soil B > soil A, which agrees with the OC content in each soil. The calculated half-lives ranged from 4.2 days for carbofuran in soil A to 330 days for prometon in soil C. As a general rule, when higher OC content in the soil the greater persistence of the pesticide was observed as a consequence of the increased adsorption. The first order kinetics model satisfactorily explains the disappearance of the studied pesticides in the soil. (Author)

[en] The dose absorbed by the material is estimated from penetration curves (electrons) or isodose curve networks (photons). The characteristics of the linear accelerator used are given, different dosimetric techniques are described and the advantages of computer-assisted dosimetry are mentioned. The use of computing programmes to evaluate dose rate leads to greater precision and appreciable time-saving. It gives excellent results in cobalt therapy and is starting to be used in the field of industrial gamma irradiations for the calculation of isodose curves. The work in progress and the first results obtained are reported

[en] While the effects of irradiation on the mechanical properties of stainless steels have been extensively investigated, most data have been obtained from relatively large specimens. However, fusion reactor materials development will require the extensive use of miniaturized specimens. Yet the synergisms between the influence of specimen size and irradiation are not well understood. Consequently, the objectives of this study were to identify and clarify the potential roles of irradiation and specimen size in tensile and creep properties of austenitic stainless steels; this is an initial step in developing a complete understanding of irradiation effects in small specimens. (author)