[en] If fatigue crack initiation is currently quite well understood for pure single crystals, its comprehension and prediction in cases of polycrystal alloys such as AISI 316LN stainless steel remain complicated. Experimentally our study focuses on the characterisation of the mechanical behaviour and on the study at different scales of the phenomenon leading to low cycle fatigue crack initiation in 316LN stainless steel. For straining amplitudes of?e/2 = 0,3 and 0,5%, the cyclic softening observed during testing has been related to the organisation of dislocations in band structures. These bands, formed due to the activation of slip systems having the greatest Schmid's factor, carry the most part of the deformation. Their emergence at free surfaces leads to the formation of intrusions and extrusions which help cracks initiate and spread. Numerically we worked on the mesoscopic scale, proposing a new model of crystalline plasticity. This model integrates geometrically necessary dislocations (GND) directly computed from the lattice curvature. Implemented in the finite element code Abaqus^TM and Cast3m^TM, it is based on single crystal finite deformations laws proposed by Peirce et al. (1983) and Teodosiu et al. (1993). Extended for polycrystals by Hoc (2001) and Erieau (2003), it has been improved by the introduction of GND (Acharya and Bassani, 2000). The simulations performed on different types of aggregates (2D/3D) have shown that taking GND into account enables:- the prediction of the grain size effect on a macroscopic and on a local scale,- a finer computation of local stress field.The influence of the elasticity and interaction matrices on the values and the evolution of the isotropic and kinematic mean stresses has been shown. The importance of boundary conditions on computed mechanical fields could also be pointed out. (author)

[en] In order to test the feasibility of Coulomb excitation of radioactive projectiles with low beam energies and intensities, they have produced a secondary radioactive beam of ⁷⁸Rb and Coulomb re-excited it. The beam was produced in the fusion evaporation reaction ²⁴Mg(⁵⁸Ni,3pn)⁷⁸Rb at a beam energy of 260 MeV, using the Argonne National Laboratory ATLAS accelerator. The residues of interest were separated from other reaction products and non-interacting beam using the Fragment Mass Analyzer (FMA). The beam leaving the FMA was ⁷⁸Kr and ⁷⁸Rb^gs,m1,m2, which was refocused onto a ⁵⁸Ni secondary target. They have extracted a spectrum of γ-rays associated with re-excitation of A = 78 isobars. The re-excitation of stable ⁷⁸Kr was observed, which serves as a reference. Gamma-rays associated with excitation of ⁷⁸Rb^gs,m1,m2 were also seen. The measured yields indicate that all the ⁷⁸Rb states are highly deformed

[en] High field superconducting magnets using high temperature superconductors are being developed for high energy physics, nuclear magnetic resonance and energy storage applications. Although the conductor technology has progressed to the point where such large magnets can be readily envisioned, quench protection remains a key challenge. It is well-established that quench propagation in HTS magnets is very slow and this brings new challenges that must be addressed. In this paper, these challenges are discussed and potential solutions, driven by new technologies such as optical fiber based sensors and thermally conducting electrical insulators, are reviewed. (author)

[en] Superconducting (Hg,Re)Ba₂CaCu₂O_y ((Hg,Re)-1212) thin films have been prepared on single crystal substrates of LaAlO₃ by reacting laser deposited ReBaCaCuO precursor films with CaHgO₂ in sealed quartz tubes. The effects of the deposition parameters such as laser fluence and substrate temperature, on surface morphology and microstructure were examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM observations revealed that a granular structure was seen in the precursor films deposited at lower energy (less than 200 mJ) and disappeared at higher energy (250 mJ). SEM investigation on final reacted films showed that the precursor films deposited at 250 deg. C resulted in a well-connected and uniformly dense microstructure, whereas the films deposited at lower or higher temperatures were porous and non-uniform

[en] That channel box is characterized in that it is constituted by several similar modules of prismatic shape, inside each of which are vertically mounted one or several fuel element bundles which are not integral with said module, the walls of said channel box being provided with means for guiding control rods, means adapted to provide emergency coolant and means for positioning measuring devices. This can be applied to light water reactors

[en] Fluorination of Pb-doped HgBa(sub 2)Ca(sub 2)Cu(sub 3)O(sub y) (Hg-1223) system was investigated. Structural and magnetic measurements reveal that fluorine addition promotes the phase formation, optimize the charge carrier concentration, and enhance flux pinning. We report an increase in both the transition temperature and the critical current density through controlled fluorine incorporation. Even a possible change in the pinning mechanism in this technologically important system is suggested

[en] Steady state engineering test reactors with high field, low current operation are investigated and compared to high current, lower field concepts. Illustrative high field ETR parameters are R = 3 m, α ∼ 0.5 m, B ∼ 10 T, β = 2.2% and I = 4 MA. For similar wall loading the fusion power of an illustrative high field, low current concept could be about 50% that of a lower field device like TIBER II. This reduction could lead to a 50% decrease in tritium consumption, resulting in a substantial decrease in operating cost. Furthermore, high field operation could lead to substantially reduced current drive requirements and cost. A reduction in current drive source power on the order of 40 to 50 MW may be attainable relative to a lower field, high current design like TIBER II implying a possible cost savings on the order of $200 M. If current drive is less efficient than assumed, the savings could be even greater. Through larger β/sub p/ and aspect ratio, greater prospects for bootstrap current operation also exist. Further savings would be obtained from the reduced size of the first wall/blanket/shield system. The effects of high fields on magnet costs are very dependent on technological assumptions. Further improvements in the future may lie with advances in superconducting and structural materials

No abstract available

[en] As Congress continues its debate on the Clean air Act, concern over air pollution, aesthetic deterioration, and encroaching development in national parks is being expressed by many factions. Park superintendants themselves cite increasing threats of irreversible damage. A case study is presented of the Golden Circle of southwestern national parks, current attempts to regulate oil, gas and uranium exploration there, and the consequences of various proposals to protect these public lands

[en] One of the consequences of the Chernobyl accident, and the break-up of the Soviet Union a few years later, was the establishment of a programme of co-operation and assistance between the East and the West on matters of nuclear safety. It was understood, however, that unless and until the countries of the East established a proper legal framework within which those co-operation activities could be carried out, progress on improving the safety of many of their existing nuclear power plants would be difficult. (author)