1,721,056 research outputs found
Design and development of a package prototype for intermediate level solid waste (ILW)
No full textThe principal objective of the job will concern the planning and the qualification of packages for intermediate level solid waste ILW (according to the new classification of the Ministerial Decree of August 7th 2015, ILW according to GSG-01 IAEA). The radioactive waste is the material containing radionuclide to superior levels to the so-called levels of leaving and for which their re-use is not foreseen. This category includes, for instance, part of the metals activated coming from the dismantlement of the primary circuits, as well as the graphite used as moderators/reflectors and other components from nuclear power plants (NPPs) under decommissioning, the radioactive waste from industrial activity, health and medical research. The project has the intention to develop a new concept - at national level - for the disposal of the intermediate level solid waste (ILW). The product is a dual-purpose package, that is qualified both for the transport and for the storage. The waste packages integrity is a crucial point for the safe disposal, storage and transport of radioactive waste. For qualification purposes, the manufacturers need to demonstrate that the waste packages can withstand loads that could occur during operation and accident conditions. The work will be divided into three phases:
PHASE I: definition of the constructive characteristics of the package;
PHASE II: realization of the packages prototypes;
PHASE III: qualification tests B(U) type.
The requirements must meet the needs for the Italian nuclear activities, currently based on the decommissioning of NPPs, the research activities and residual industrial activities. There is also a need to maintain a very high level of safety during the life of the packages. All over the world, in analogous way to what happens in our Country, the management of the radioactive waste is increasingly a remarkable practice. All States have radioactive residues that are produced by various activities, as the production of electricity in electric nuclear powers, the management of fittings of the nuclear fuel’s cycle, a series of applications of the radioisotopes in medical, industrial, agricultural, research and education field. It is of utmost importance for the aforesaid category of waste, to study and to plan some packages, that maintain very elevated level of safety during their useful life, that is expected around 100 years
An OpenFOAM multi-region solver for tritium transport modeling in fusion systems
Full text linkThe transport, permeation and retention of tritium inside nuclear fusion reactors is a topic of great interest due to the scarcity of the isotope, its ease of diffusion through materials and its radioactivity. An accurate balance of tritium is needed in all the fuel cycle, and each loss term needs to be evaluated in detail. In this context, reliable and flexible tools to evaluate tritium permeation and retention are a necessity for the development of fusion technologies. This work presents the OpenFOAM PermeAtion Solver for Tritium Analysis Foam (pastaFoam) solver and two custom boundary conditions, along with a series of verification and validation cases. The solver inherits all capabilities of the base solver, chtMultiRegionFoam, and is capable to simulate hydrogen transport in coupled fluid-solid systems in the presence of hydrogen traps, under diffusion limited regime or accounting for surface effects. All features are tested against analytical solutions and results are compared with other tritium transport codes. Agreement with experimental data is aligned with results of numerical benchmarks from literature
Modeling of a confinement bypass accident with CONSEN, a fast-running code for safety analyses in fusion reactors
No full textThe CONSEN (CONServation of ENergy) code is a fast running code to simulate thermal hydraulics transients, specifically developed for fusion reactors. In order to demonstrate CONSEN capabilities, the paper deals with the accident analysis of the magnet induced confinement bypass for ITER design 1996. During a plasma pulse, a poloidal field magnet experiences an over-voltage condition or an electrical insulation fault that results in two intense electrical arcs. It is assumed that this event produces two one square meters ruptures, resulting in a pathway that connects the interior of the vacuum vessel to the cryostat air space room. The rupture results also in a break of a single cooling channel within the wall of the vacuum vessel and a breach of the magnet cooling line, causing the blow down of a steam/water mixture in the vacuum vessel and in the cryostat and the release of 4 K helium into the cryostat. In the meantime, all the magnet coils are discharged through the magnet protection system actuation. This postulated event creates the simultaneous failure of two radioactive confinement barrier and it envelopes all type of smaller LOCAs into the cryostat. Ice formation on the cryogenic walls is also involved. The accident has been simulated with the CONSEN code up to 32 hours. The accident evolution and the phenomena involved are discussed in the paper and the results are compared with available results obtained using the MELCOR code
Design and analysis of the improved configuration of the secondary circuit for the EU-DEMO power plant
No full textDEMO is planned to be a prototype fusion power plant capable of demonstrating production of electricity at the level of a few hundred MW. DEMO is considered to be an intermediate step between the ITER experimental reactor and a commercial power plant. Design and assessment studies on the European (EU) DEMO are carried out by the EUROfusion consortium. The Primary Heat Transfer System (PHTS) transfers heat from the breeding blanket (BB) and other reactor heat sources (divertor and vacuum vessel) to the secondary circuit. Two main BB concepts, and the respective PHTSs, for EU-DEMO are considered: the Helium Cooled Pebble Bed (HCPB) BB and the Water Cooled Lithium Lead (WCLL) BB. Two variants for each concept are possible: with or without the Intermediate Heat Transfer System (IHTS), including the Energy Storage System (ESS), between the PHTS and the Power Conversion System (PCS), which generates electricity. The role of IHTS and ESS is to prevent energy pulses obtained by BB PHTS during the plasma burns to be directly transferred to PCS. In 2017 we proposed the first concept of the PCS configuration for the option WCLL BB with the ESS, which enabled almost constant generation of electricity during both plasma pulse and dwell phases. However, we observed some disadvantages of this concept, which had to be cured, i.e., excessive temperature differences between the pulse and dwell phases in several heat exchangers. In the present paper, we describe the GateCycle model of the improved PCS configuration for the WCLL BB with the ESS option, which ensures not only almost constant electricity production during both plasma pulse and dwell phases, but also acceptably small temperature fluctuations |T pulse -T dwell | in all the circuit components, which should prevent their failure due to excessive thermal stress
Metodologia per l’analisi delle quantità integrali misurate nell’esperienza benchmark e loro correlazione con quelle relative al reattore di riferimento
No full textAn experimental study on the air-side heat transfer coefficient and the thermal contact conductance in finned tubes
No full textThe objective of the present experimental study is to evaluate the heat transfer coefficient outside a tube with annular transverse fins, derived from strips of copper mechanically bounded and coupled outside. Water was used as heating medium, in turbulent conditions and flowing at different temperatures inside the tube. Petukhov’s correlation has been selected to calculate water heat transfer coefficient in the tube. The experimental data obtained have been compared with a correlation from literature, and a similar trend has been observed. A fitting of the data provided a correlation for the three tubes of different external diameter (30 mm, 22 mm and 15.6 mm) which agree very well with the experimental values. The thermal contact conductance has been identified as the main reason for the difference between data and original Briggs and Young’s correlation. An estimation of the contact conductance between fins and tubes provided values between 3500 and 11000 W/m2K, slightly increasing with the air Reynolds number (based on the external diameter of the tube), whose range is 2000 to 8000. The thermal contact resistance has been estimated and its importance has been confirmed, contributing for 30 to 50% to the total air-side thermal resistance in the tubes used in the experiments
Determinazione dei parametri di sicurezza del core e dell’andamento del burnup di un reattore veloce refrigerato a metallo liquido
No full textIn questo rapporto vengono documentate le attività svolte per lo sviluppo e la validazione di un modello Monte Carlo basato sul codice MCNPX v.2.7 per la
simulazione neutronica di un reattore veloce raffreddato a sodio. Tale modello è stato sviluppato seguendo le specifiche dell’OECD/NEA Sodium Task Force. I principali parametri nucleari del core (coefficienti di reattività, parametri nucleari, distribuzione tridimensionale della potenza e concentrazione degli attinidi) sono stati calcolati per un nocciolo all’equilibrio, ad inizio ed alla fine del ciclo. I risultati ottenuti sono stati sottomessi all’OECD/NEA ed il confronto preliminare con altre soluzioni indipendenti dimostra il buon accordo dei dati calcolati. I risultati di questo lavoro verranno utilizzati per lo sviluppo di un modello termoidraulico di un SFR utilizzando il codice RELAP5-3D©
A Preliminary Exergy Analysis of the EU DEMO Fusion Reactor
Full text linkPurpose of the present study is the exergy analysis of EU DEMO pulsed fusion power plant considering the Primary Heat Transfer Systems, the Intermediate Heat Transfer System (IHTS) including the Energy Storage System (ESS) as a first option to ensure the continuity of electric power released to the grid. A second option here considered is a methane fired auxiliary boiler replacing the ESS. The Power Conversion System (PCS) performance is evaluated as well in the overall balance. The performance analysis is based on the exergy method to specifically assess the amount of exergy destruction determined by irreversible phenomena along the whole cyclic process. The pulse and dwell phases of the reactor operation are evaluated considering the state of the art of the ESS adopting molten salts alternate heating and storage in a hot tank followed by a cooling and recovery of molten salt in a cold tank to ensure the continuity of power release to the electrical grid. The second option of the plant configuration is evaluated on the basis of an auxiliary boiler replacing the ESS with a 10% of the power produced by the reactor during both pulse and dwell modes
Experimental investigation on pure steam and steam-air mixture condensation inside Tubes
Full text linkExperiments on steam condensation inside inclined tubes were carried out with the following aims: a) to investigate the physical phenomena involved in condensation of steam within tubes; b) to study the influence of the geometry (namely, tube inclination) on the heat transfer rate, also in presence of high concentration of non-condensables; c) to develop models and heat transfer correlations for these conditions; d) to produce a database for modeling in-tube condensation with high percentage of non-condensable gases. Steam and steam-air condensation experiments were carried out in gravity controlled stratified flow regime inside a horizontal and inclined tube (22 mm inside diameter) and the average heat transfer coefficient has been evaluated. For pure steam condensation, the experimental data were compared with literature correlations and their agreement has been verified, suggesting some minor modifications. A limited influence of tube inclination on heat transfer has been observed: condensation in the presence of non-condensable gases is not sensibly affected by inclination, especially at high gas concentrations. Two empirical correlation are proposed to be used in the preliminary design of a condenser in a passive containment cooling system, as in thermal-hydraulic simulation, especially in transient conditions, when a high gas concentration is present
Attività propedeutiche per la messa in funzione di un impianto termoidraulico ad alta pressione per pretest su simulacri di componenti
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