Buckling of Imperfect Thin Cylindrical Shell under Lateral Pressure

The strength of thin shells, under external pressure, is highly dependent by the nature of imperfection. This paper investigates buckling behaviour of imperfect thin cylindrical shells with analytical, numerical, and experimental methods in conditions for which, at present, a complete theoretical analysis was not found in literature. In general, collapse is initiated by yielding, but interaction with geometrical instabilities is meaningful, in that imperfections reduce the load bearing capacity by an amount of engineering significance also when thickness is considerable. The aim of this study was to conduct experiments that are representative of buckling, in the context of NPP applications as, for instance, the IRIS (international reactor innovative and secure) and LWR steam generator (SG) tubes. At Pisa University, a research activity is being carried out on the buckling of thin walled metal specimen, with a test equipment (and the necessary data acquisition facility) as well as numerical models were set up by means FEM code. The experiments were conducted on A-316 test specimens, tubes with and without longitudinal welding. The numerical and experimental results comparison highlighted the influence of different types of imperfections on the buckling loads with a good agreement between the finite-element predictions and the experimental data

Performance of a type IP-2 packaging system in accident conditions of transport

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.A package to be used for the transport of hazardous /radioactive materials must demonstrate to fulfil the International standards requirements in order to provide protection to the human being and environment even under accident conditions, such as rigorous fire events. In these conditions, the system (package or cask), constituted, in general, by a massive sealed steel vessel, must thus demonstrate to be robust, safe and reliable so to guarantee both structural strength and radiation shielding. The present study deals with the evaluation of the thermostructural response and performance of an Italian design type IP-2 packaging system, provided by Sogin, that should be adopted for the transportation of low and intermediate level radioactive solid/solidified wastes. To evaluate its performance, a FEM model has been set up and implemented in a rather refined way taking into account all the packaging system components. Numerical simulations addressed fire scenarios as specified in the IAEA regulations: packaging subjected to an engulfing fire of 800 °C for 30 minutes. All the heat transfer mechanisms, inside the system and between the system itself and the environment, have been considered in the thermal analyses performed. The results of the thermal analyses are presented and discussed. Analysing the results obtained it is possible to conclude that although any potential damage the integrity of IP2 packaging system is assured.cf201

Numerical evaluation of sloshing effects in ELSY innovative nuclear reactor pressure vessels seismic response

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.In Europe a great effort has been made in the Lead-Bismuth Eutectic (LBE) technology, for use in the sub-critical reactors, and its natural development is represented by the use of pure lead that is less corrosive, chemically inert and in the foreseen environment has good neutronic and thermal-hydraulic characteristics, therefore it appears to be a suitable coolant for a fast reactor. The main purpose of this study deals with the evaluation of the sloshing dynamic effects of lead coolant during a safety shut down earthquake applied to a conceptual Lead-cooled Fast Reactor (LFR) Generation IV (GEN IV) Nuclear Power Plant design, with reference to the ELSY project system configuration that is under development within the ongoing European 7FW ELSY Program. ELSY is an innovative small size pool-type reactor (600 MWe) cooled by pure lead, characterized by a compact and simple integrated primary circuit; by the way this configuration is favourable from the point of view of the reduction of the seismic loads and of the negative effect of the high lead density. Therefore, the fluid-structure interaction problems and the free oscillations of the heavy metal primary coolant attracted the attention because during a strong motion earthquake the lead surrounding the internals may be accelerated and the so-called hydrodynamic interaction, due to the coolant sloshing, may significantly influence the stress level in the reactor pressure vessel (RPV). To the purpose, the effect of the rigidity of adjacent internals walls and coupling between coolant and vessel are considered An adequate numerical modelling, by means a 3-D finite element model, was set up and used for the foreseen structures dynamic analysis, due to the inability of linear theory to describe accurately the wave’s motion accounting for the complex considered RPV geometrical aspect as well as the material nonlinearities. Numerical results are presented and discussed highlighting the importance of the fluid-structure interaction effects in terms of stress intensity as well as the capacity of internals and vessel walls to withstand wave’s impact and prevent instabilities.vk201

Performance of a type IP-2 packaging system in accident conditions of transport

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.A package to be used for the transport of hazardous /radioactive materials must demonstrate to fulfil the International standards requirements in order to provide protection to the human being and environment even under accident conditions, such as rigorous fire events. In these conditions, the system (package or cask), constituted, in general, by a massive sealed steel vessel, must thus demonstrate to be robust, safe and reliable so to guarantee both structural strength and radiation shielding. The present study deals with the evaluation of the thermostructural response and performance of an Italian design type IP-2 packaging system, provided by Sogin, that should be adopted for the transportation of low and intermediate level radioactive solid/solidified wastes. To evaluate its performance, a FEM model has been set up and implemented in a rather refined way taking into account all the packaging system components. Numerical simulations addressed fire scenarios as specified in the IAEA regulations: packaging subjected to an engulfing fire of 800 °C for 30 minutes. All the heat transfer mechanisms, inside the system and between the system itself and the environment, have been considered in the thermal analyses performed. The results of the thermal analyses are presented and discussed. Analysing the results obtained it is possible to conclude that although any potential damage the integrity of IP2 packaging system is assured.cf201

Sloshing effects in innovative nuclear reactor pressure vessels

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The reactor pressure vessel is a cylindrical shell structure which contains a rather large amount of liquid and many structures. Therefore, the fluid-structure interaction problems and the free oscillation of an incompressible liquid have attracted the attention because during a postulated earthquake (e.g. Design Basis Earthquake) the primary coolant surrounding the internals is accelerated and a significant fluid-structure hydrodynamic interaction is induced: in particular, the so called coolant “sloshing” influence on the stress level in the RPV. This effect is mainly important in the case of liquid metal primary coolant case and its coupling with the reactor vessel and its internals are considered. Numerical modelling proved to be very useful for the foreseen structures analysis because neither linear nor second-order potential theory is directly applicable when steep waves are present and high-order effects are significant. In what follow numerical results are presented and discussed highlighting the importance of the fluid-structure interaction effects in terms of stress intensity and were also used in order to obtain a preliminary validation of the numerical approach/models in comparison with experimental data.cs201