[en] Employing the realistic matrix elements calculated by Kuo and Brown for the Hamada-Johnston nucleon-nucleon potential, a number of nuclei in the 0f-1p shell are studied within the framework of shell-model and quasiparticle methods. Specifically, shell-model calculations are performed for ⁵¹Ti and ⁵²V, which have neutrons and protons in well separated shells outside the closed ⁴⁸Ca core. In studying ⁵¹Ti, in addition to the three-nucleon configurations, some four-particle-one-hole configurations due to the excitation of the core are also included. With ⁴⁰Ca as a core, shell-model calculations are carried out for ⁴³Sc and ⁴³Ca, and a comparative study of the level structure, transition rates, and spectroscopic strengths of ⁴⁴Ca is performed, employing the conventional shell model and Kuo-Brown and Clement matrix elements for the Hamada-Johnston and Tabakin interactions, respectively. For the heavier even isotopes of Ca, quasiparticle calculations are performed and the results are compared with the available data. Calculations on the energy levels and transition rates of ⁵²Cr, ⁵⁴Fe, and ⁵⁶Ni employing the quasiparticle method, with a ⁴⁸Ca core, are also carried out. (U.S.)

No abstract available

[en] A method for simulating the pulse height responses of passive gamma ray spectroscopy logging tools is described and its application to measurements of radioactive tracer spectra is demonstrated. Comparison of simulated and measured calibration spectra for several tracers illustrates the accuracy and utility of the method which is now being used to extend the applications to additional tracer isotopes and other wellbore geometries

[en] The main function of the post-tensioning system is to provide the primary concrete containment with the capability to resist the tension forces caused by internal accident pressure. This function is accomplished by introducing permanent, counteracting compression forces. The post-tensioning system consists of high strength wire or strand tendons placed inside ducts formed within the containment walls and dome. Each tendon end is attached to an anchorhead which transfers the highly stressed tendon tension load to steel bearing plates embedded in concrete. The exposed ends of of the tendons are sealed with steel caps and the entire system is protected against corrosion by filling the void area in the ducts and caps with a specially formulated petroleum grease. (orig.)

No abstract available

[en] Nuclear well logging tools produce data which are inherently statistical in nature. A number of algorithms have been used to smooth such data to enhance visual clarity and to improve robustness for subsequent log analysis. Techniques have recently been developed to display better vertical resolution on processed nuclear log measurements and thus provide better evaluation of thinner beds in earth formations. In this paper a theoretical justification for such procedures is developed which emphasizes the need to keep in mind the physics of the measurement process. A fast and simple filtering algorithm is then described which combines smoothing and partial deconvolution. The mathematical details are sketched for this procedure. The utility of the technique is illustrated using the system response function for a gamma ray tool and corresponding log data from an actual well

[en] Full text of publication follows: Helium is produced in neutron-irradiated metals by (n,a) transmutation reactions and because of its very low solubility in metals it plays a very important and specific role in microstructural evolution and mechanical properties degradation. Helium is initially interstitial, and recent first principles Density Functional Theory (DFT) calculations performed in iron and tungsten predict that it has a tetrahedral rather than octahedral configuration at variance with what is expected from empirical potentials. DFT calculations of the solution energies of helium in substitutional, tetrahedral and octahedral sites have been performed for all BCC transition metals: V, Nb, Ta, Cr, Mo, W and Fe. The effects of exchange correlation functional and of pseudopotential have been investigated in Fe; they are relatively small. The solution energies are found to be weakly dependent on the element for the substitutional site whereas for the interstitial sites they are much smaller in group V than in group VI and they decrease from 3d to 4d and 5d metals. As a result an inversion is observed from V, Nb and Ta - which tend to favor the interstitial site - to Mo and W, which favor the substitutional one, with an intermediate behavior for Cr and Fe. The tetrahedral site is always energetically more favorable than the octahedral one by 0.2 to 0.3 eV. Finally, the He-vacancy dissociation energies deduced from these calculations are found to range from 0.7 eV in V to 4.5 eV in W, with a systematic increase as a function of group and within a group. These energies are in excellent agreement with THDS experimental data available in Mo and W. (authors)

[en] Full text of publication follows: In fusion reactors, helium is one of the main gaseous by-products produced as a result of high energy neutron irradiation. In the case of ferritic steels to be used in future fusion and fission reactors, the formation of helium bubbles at grain boundaries (GBs) leads to drastic modification of the material's mechanical properties such as high temperature embrittlement. A quantitative description of the interaction of He atoms with grain boundaries is therefore essential. First principles calculations provide such information at an atomic scale which is not directly accessible through experiments. In this work, a 'dynamic coupling' of ab initio and MD simulations has been performed to study the properties of representative symmetric tilt grain boundaries in Fe. More specifically, density functional theory within the Generalised Gradient Approximation code is used to calculate the structural, energetic and magnetic properties of certain GBs in bicrystals which contain a few hundred atoms. The lowest energy binding sites of He atoms at these GBs are also investigated. These results are compared to empirical potential calculations of similar and much larger systems. Such a coupling enables an in-depth study of GBs by incorporating predictive ab initio calculations which are essential for the validation of the existing empirical potential or the fitting of new ones, while the empirical simulations are necessary to study the finite temperature effects on these properties as well as providing an understanding of simulation cell size effects. The present study is the first step towards a predictive description of the segregation of He at GBs and their embrittling effects in the steels. (authors)

[en] Fe and Cr have a complex magnetic behavior. This complexity is already present in some bulk phases like spin spirals of face centered Fe or spin density wave (SDW) of Cr. SDW can be described qualitatively by density functional theory (DFT) or tight binding (TB) calculations, which predict its shape and polarization in agreement with experimental findings. The energy of defects as surfaces or vacancies, and also FeCr alloy energetics are influenced by magnetism. At the same time, defects can modify local magnetic structure and create complex non collinear magnetic patterns. (authors)

[en] Full text of publication follows: The diffusion of He in a-Fe in the presence of defects produced by irradiation (vacancies and self-interstitials) is studied using both rate theory and kinetic Monte Carlo models with input from ab initio calculations. Comparison between the model based on He in pure Fe and experimental data of He desorption from Fe under different conditions shows discrepancies. Increasing the vacancy migration energy and decreasing the binding energy of a vacancy to a He substitutional and a vacancy to a He interstitial provides good agreement with experimental measurements at all temperatures and conditions studied. This difference in energies from the original ab initio data for pure Fe is attributed to the presence of impurities in the experimental samples, with carbon being the most likely candidate. In order to check the validity of this assumption, ab initio calculations were performed to study the energetics of He-V-C complexes in α-Fe. These data have been included in a full model of He migration in α-Fe in the presence of carbon. Calculations are presented on the effect of carbon on He migration for different conditions, in particular different He-to-vacancy ratios, temperatures and carbon concentrations. Finally the effect of carbon on He desorption in α-Fe is evaluated. This work was performed in the framework of the European Fusion Materials Modelling programme. (authors)