[en] Evaluation of material buckling for heterogenous nulcear reactors is a key-problem for reactor people. In this direction several methods have been elaborated: bi-group method, heterogenous method and perturbation methods. Out of them, mostly employed is the perturbation method which is also presented in this paper and is applied in some parameter calculations of a new cell type for which fuel is positioned in the marginal area and the moderator is in the centre. It is based on the technique of progressive substitution. Advantages of the method: buckling comes out clearly, high level defects due to differences between O perturbated fluxes and the unperturbated flux Osub(o) can be corrected by an iterative procedure; using a modified bi-group theory, one can clearly describe effects of other parameters

[en] Composite construction materials with a layered structure may have various imperfections in the interlayer adhesion due to the technology used for their manufacture or their service conditions. In particular, this may involve defects of the crack type. Upon compression along such defects, the classical criteria for fracture (Griffith-Irwin or its generalization) cannot be used, since in this situation all the stress intensity factors and the openings of the sides of the crack are equal to zero, the onset of the process of fracture of the composite upon compression along cracks was hypothesized to be connected with loss of stability (buckling) in the vicinity of the crack. In investigation of the stability of a composite with cracks, different applied calculation schemes have been used by different authors: rod, shell, etc., and also approximate theories such as (for example) continuum theory. And within the framework of the latter, we cannot distinguish between interlayer and intralayer cracks. In this paper, within an exact formulation we consider the stability of a composite in compression along two parallel structural cracks located at the layer interfaces

[en] Since the new millennium, truss PCMs(Periodic Cellular Metals) have drawn attention because of their superior specific stiffness, strength and multi-functionality. Prior studies have focused on the structural design and optimization. Kagome truss PCM has been proved to have the higher resistance to plastic buckling, more plastic deformation energy and lower anisotropy than other truss PCMs. In this study, we introduce a new idea to fabricate multi-layered Kagome truss PCM from continuous wires which can gain high strength as in piano wires and can be controlled to be defect free owing to drawing process. The relative density, the stiffness and the strength under bending and compressive load are estimated through elementary mechanics and compared with the results from experiments and FEA. The failure mechanisms are analyzed, and also mechanical performance and production are discussed

[en] In introductory reactor physics courses the four-factor-formula and two-group theory is normally used to demonstrate to students in a quantitative way the physics of nuclear reactors. However, the agreement obtained between lattice calculations with such simple recipes and measurements is not very good. This is in particular the case for light water reactors. To improve this situation it has been investigated whether it is possible by relative simple modifications of such a recipe to obtain better agreement between theory and measurements. The results obtained from this investigation are presented in this paper. It is seen from the results that significant improvements in the agreement between measurements and theory have been obtained. This report was presented to the meeting on Reactor Physics Calculations in the Nordic Countries, Helsinki, May 8-9, 1995. (au)

[en] The stability and post-buckling response of simple perfect and imperfect systems made of non-linear elastic material are thoroughly discussed. The perfect systems correspond to the three types of bifurcation points, i.e. stable symmetric, unstable symmetric and asymmetric. Material-dependent stability conditions are properly established. It is found that the mechanisms of buckling of perfect systems associated with a stable symmetric bifurcation point may become unstable depending on the value of the material nonlinearity parameter. Moreover, it is established that the effect of compressibility on the buckling load may be considerable in case of imperfect systems which in their ideal state are associated with anasymmetric bifurcation point. (orig.)

[en] Flexure of cylinders and slightly curved pressurized tubes is investigated for given conditions on the edges, in particular for end flanges. The large precritical deformation is determined with the help of the Flexible-Shell-Theory. The stability analysis of the deformed shell is carried out with the aid of the hypothesis of local buckling. The critical bending moments which determine the collapse load are presented for various tube lengths, initial curvatures and external-pressure values by graphs. (orig.)

[en] The purpose of this study is to investigate the dynamic interaction between a reactor vessel and equipment in elastic and inelastic domains when subjected to earthquakes. Two types of coupled two degrees of freedom systems were considered. One represents coaxial cylindrical vessels, such as a reactor vessel and a thermal shield. A narrow gap between them is filled with liquid, and the interaction between the structures occurs due to the liquid. Another type represents a reactor vessel and self standing core components supported by the vessel. It is also the purpose to evaluate the seismic safety margin of reactor vessels against buckling including postbuckling behavior. The evaluation is based on the nonlinear seismic response of a single degree of freedom system with nonlinear restoring force. The models of a coaxial cylindrical vessel and a reactor vessel with self standing core components are explained. The results of the elastic response analysis, the nonlinear response analysis and so on are reported. The seismic force applied to the vessel can be reduced by the liquid-coupled effect and the modal contribution effect. The vessel can withstand larger seismic excitation. (K.I.)

No abstract available

[en] In this work is being analysed the possibility for preserving the flat flux in the central zone of the two-zone reactor. Interdependence of the radius of the flat central zone and radial buckling in the outer zone for an adopted form factor is obtained. The numerical procedure for solving a system of two non-linear equations which is the mathematical model is analysed. There is a preposition procedure for removing and exchange of fuel in both zones of a heavy water reactor, with the intention to maintain the flat zone of reactor operation. (author)

[en] Stability is dealt with, in accordance with the regulations and specifications, as the deformation of a cylinder under external hydrostatic pressure. The inner rings/tubes can, in fact, become instable. However, the load capacity depends on the size of the disturbance which in real components always exists between inner and outer walls. With real disturbances, the limit load is most always determined by yielding point and stress at failure; it is within the stable range of equilibrium. With loads in the plastic range of the material, the critical load can be determined taking into account a plastic joint, and subsequently compared with the load resulting from the stress computational method developed by Cozzone. In this calculation, a non-linear stress distribution accross the cross section is assumed. (orig./HP)