Pre-test analysis of protected loss of primary pump transients in CIRCE-HERO facility

In the frame of LEADER project (Lead-cooled European Advanced Demonstration Reactor), a new configuration of the steam generator for ALFRED (Advanced Lead Fast Reactor European Demonstrator) was proposed. The new concept is a super-heated steam generator, double wall bayonet tube type with leakage monitoring [1]. In order to support the new steam generator concept, in the framework of Horizon 2020 SESAME project (thermal hydraulics Simulations and Experiments for the Safety Assessment of MEtal cooled reactors), the ENEA CIRCE pool facility will be refurbished to host the HERO (Heavy liquid mEtal pRessurized water cOoled tubes) test section to investigate a bundle of seven full scale bayonet tubes in ALFRED-like thermal hydraulics conditions. The aim of this work is to verify thermofluid dynamic performance of HERO during the transition from nominal to natural circulation condition. The simulations have been performed with RELAP5-3D© by using the validated geometrical model of the previous CIRCE-ICE test section [2], in which the preceding heat exchanger has been replaced by the new bayonet bundle model. Several calculations have been carried out to identify thermal hydraulics performance in different steady state conditions. The previous calculations represent the starting points of transient tests aimed at investigating the operation in natural circulation. The transient tests consist of the protected loss of primary pump, obtained by reducing feed-water mass flow to simulate the activation of DHR (Decay Heat Removal) system, and of the loss of DHR function in hot conditions, where feed-water mass flow rate is absent. According to simulations, in nominal conditions, HERO bayonet bundle offers excellent thermal hydraulic behavior and, moreover, it allows the operation in natural circulation

Post-test simulation of a PLOFA transient test in the CIRCE-HERO facility

CIRCE is a lead–bismuth eutectic alloy (LBE) pool facility aimed to simulate the primary system of a heavy liquid metal (HLM) cooled pool-type fast reactor. The experimental facility was implemented with a new test section, called HERO (Heavy liquid mEtal pRessurized water cOoled tubes), which consists of a steam generator composed of seven double-wall bayonet tubes (DWBT) with an active length of six meters. The experimental campaign aims to investigate HERO behavior, which is representative of the tubes that will compose ALFRED SG. In the framework of the Horizon 2020 SESAME project, a transient test was selected for the realization of a validation benchmark. The test consists of a protected loss of flow accident (PLOFA) simulating the shutdown of primary pumps, the reactor scram and the activation of the DHR system. A RELAP5-3D© nodalization scheme was developed in the pre-test phase at DIAEE of “Sapienza” University of Rome, providing useful information to the experimentalists. The model consisted to a mono-dimensional scheme of the primary flow path and the SG secondary side, and a multi-dimensional component simulating the large LBE pool. The analysis of experimental data, provided by ENEA, has suggested to improve the thermal–hydraulic model with a more detailed nodalization scheme of the secondary loop, looking to reproduce the asymmetries observed on the DWBTs operation. The paper summarizes the post-test activity performed in the frame of the H2020 SESAME project as a contribution of the benchmark activity, highlighting a global agreement between simulations and experiment for all the primary circuit physical quantities monitored. Then, the attention is focused on the secondary system operation, where uncertainties related to the boundary conditions affect the computational results

Il fenomeno del food waste: gli sprechi alimentari da problema a risorse

Il tema degli sprechi alimentari rappresenta un problema globale nonché una preoccupazione centrale del nostro secolo. Negli ultimi anni, il fenomeno ha assunto un’importanza crescente all’interno del dibattito scientifico e delle iniziative della società civile, fino ad essere richiamato nei documenti programmatici dell’UE e delle principali organizzazioni internazionali (FAO, UNEP, USDA, G20). Tuttavia, non esiste ancora una definizione univoca di “spreco alimentare”, così come non esistono metodologie uniformi per calcolarlo; ma, gli studi concordano che il cibo è sprecato ad ogni stadio della filiera alimentare. Si stima che annualmente nel mondo gli sprechi alimentari ammontano a circa 1.3 miliardi di tonnellate (un terzo della produzione totale di cibo destinato al consumo umano). Le cause sono molteplici e si differenziano in base al livello di sviluppo economico raggiunto (Paesi industrializzati o in via di sviluppo) e in base alla particolare struttura della filiera agroalimentare (es. standard dimensionali ed estetici, norme sulla qualità dei prodotti, surplus produttivi o fattori economici). Nel panorama europeo, i Paesi che hanno già avviato azioni e programmi volti a comprendere e contrastare il fenomeno sono molti; ma solo Francia e Italia, nel 2016, hanno adottato una legislazione nazionale in materia. Gli sprechi alimentari generano impatti negativi ambientali ed economici, ma a rendere ancora più allarmante il fenomeno è la questione sociale. Infatti, a fronte di un miliardo circa di persone nel mondo che, allo stato attuale sono sottoalimentate, gli sprechi alimentari appaiono quanto mai inaccettabili. Per stimare l’impatto ambientale di un alimento sprecato è necessario considerare il suo intero ciclo di vita utilizzando indicatori specifici quali il carbon footprint, l’ecological footprint o il water footprint; mentre per quanto riguarda l’impatto economico degli sprechi, esso include la quantificazione delle esternalità negative oltre il costo o il prezzo dei prodotti gettati via. Viste le dimensioni assunte dal fenomeno e soprattutto dalla portata dei suoi impatti, gli sprechi alimentari si allontanano di molto da quelli che sono gli obiettivi di sostenibilità da intraprendere a livello mondiale. Pertanto, la promozione di iniziative di sensibilizzazione e di recupero degli sprechi (es. attraverso il recupero delle eccedenze produttive a fini solidali o per la produzione di bioenergie), oltre all’applicazione di un quadro legislativo, dovrebbe far crescere la consapevolezza di consumatori, produttori, istituzioni e politica che in un mondo in crisi economica, ambientale e sociale, lo spreco è un fenomeno totalmente insostenibile, e non è più consentito. La sostenibilità non può più essere considerata un mero concetto teorico, ma è necessario ripensare i modelli di produzione e di consumo, rivedere comportamenti e stili di vita, per intraprendere un percorso mirato verso una società compatibile con i bisogni delle attuali e delle future generazioni. In tale contesto, la Commissione europea ha presentato un pacchetto per sostenere la transizione dell’UE verso un’economia circolare, nel quale la prevenzione e la minimizzazione degli sprechi alimentari sono parte integrante.Food waste is a global issue and a central concern of our century, it is a significant phenomenon that is currently at the heart of academic debates, civil society initiatives, and political agendas (FAO, UNEP, USDA, G20). However, there is not any standardized definition of “food waste” or any homogeneous and comparable data, but all studies agree that food is wasted at every stage of the food supply chain. Annual global food waste is estimated to be about 1.3 billion tons (a third of the total food production intended for human consumption). There are many causes of waste, differentiated according to the State (industrialized or developing countries) and the various stages of the food supply chain (e.g. due to sizing and esthetic standards, product quality regulations, production surplus or economic factors). Many EU Member States have already launched actions and programmers to promote waste reduction; but only France and Italy, in 2016, have adopted a national regulation to minimize the phenomenon. Food waste have negative environmental and economic impacts and their existence raises serious questions from a social point of view. In fact, given the problem of malnutrition that is afflicting around one billion people worldwide, the food waste appears extremely unacceptable. In order to estimate the environmental impact of a wasted food, it is necessary to consider its entire life cycle using the indicators, such as carbon footprint, ecological footprint, water footprint. The economic impact of wasted food includes calculating the negative externalities, besides the cost or the price of the products thrown away. Given the scale reached by the food waste phenomenon, and above all the scope of its impacts, the food waste deviate very far from those that are the sustainability goals to be taken globally. Therefore, the promotion of awareness initiatives and waste recovery (e.g. by distribution of the productive surplus to solidarity aims or to produce bioenergy), the application of a regulatory framework, should raise consumer, producer, institution and policy awareness in a world in economic, environmental and social crisis where the waste is no longer allowed. Sustainability can no longer be considered a theoretical concept, but is necessary a rethinking of the conventional models of production and consumption, the behaviors and lifestyles, to undertake a focused path towards a society compatible with the needs of the present and the future generations. In this context, European Commission put forward to support the EU’s transition to a circular economy, where food waste prevention and minimization are an integral part

Investigation on RELAP5-3D© capability to predict thermal stratification in liquid metal pool-type system and comparison with experimental data

A numerical activity, aimed to evaluate the capability of RELAP5-3D© to reproduce the main thermal-hydraulic phenomena in an HLM pool-type facility, in different operative conditions, is presented. For this purpose, the experimental campaign performed in CIRCE-ICE test facility has been selected for the code assessment. Two experimental tests have been analyzed: TEST A consisting in a transition from no-power to a full power steady state conditions, and TEST I, consisting in a transition from gas-enhanced circulation to natural circulation, simulating a protected loss of heat sink plus a loss of flow accident. Three different pool modelling approaches are presented, consisting in a single vertical pipe, parallel pipes with cross junctions and multi-dimensional component. The comparison with experimental data has highlighted the need to divide the large pool in several sections to reproduce the natural convection, strictly correlated with the thermal stratification. The multi-dimensional component seems to be the best practice for the evaluation of this phenomenon even if the lack of specific correlation for heat transfer coefficient in quasi-stagnant conditions in large tanks is a limit for the accuracy of the results. In addition, the paper presents a detailed nodalization of the fuel pin bundle, highlighting quite good capabilities of RELAP5-3D as a subchannel analysis code

Novel Approach to Rainfall Rate Estimation based on Fusing Measurements from Terrestrial Microwave and Satellite Links

Reliable, cheap and accurate measurements of rainfall rate are growing to be more and more important in many sectors as: meteorology, agriculture, flood warning, and weather forecasting. Recently, indeed, the development of novel competitive techniques has been pushed in order to improve accuracy and reliability performance, such as commercial microwave links and broadcast satellite links. The aim of the current paper is to extend previous works of the literature based on land wireless links only. The basic idea consists in synergically employing both land and satellite based approaches together, by collecting and properly fusing the corresponding measurements. To this end, an iterative optimization procedure has been developed. As shown by numerical results, the proposed procedure gives the estimated rainfall map with a considerable accuracy and improved performance respect to the conventional algorithm based on terrestrial link only

Boundary-layer Flows Past an Hemispherical Roughness Element: DNS, Global Stability and Sensitivity Analysis

We investigate the full three-dimensional instability mechanism arising in the wake of an hemispherical roughness element immersed in a laminar Blasius boundary layer. The inherent three-dimensional flow pattern beyond the critical Reynolds number is characterized by coherent vortical structures called hairpin vortices. Direct numerical simulation is used to analyze the formation and the shedding of hairpin packets inside the shear layer. The first bifurcation characteristics are investigated by global stability tools. We show the spatial structure of the linear direct and adjoint global eigenmodes of the linearized Navier-Stokes operator and use structural sensitivity analysis to locate the region where the instability mechanism acts. Results show that the “wavemaker” driving the self-sustained instability is located in the region immediately past the roughness element, in the shear layer separating the outer flow from the wake region

Second-order perturbation of global modes and implications for spanwise wavy actuation

AbstractSensitivity analysis has successfully located the most efficient regions in which to apply passive control in many globally unstable flows. As is shown here and in previous studies, the standard sensitivity analysis, which is linear (first order) with respect to the actuation amplitude, predicts that steady spanwise wavy alternating actuation/modification has no effect on the stability of planar flows, because the eigenvalue change integrates to zero in the spanwise direction. In experiments, however, spanwise wavy modification has been shown to stabilize the flow behind a cylinder quite efficiently. In this paper, we generalize sensitivity analysis by examining the eigenvalue drift (including stabilization/destabilization) up to second order in the perturbation, and show how the second-order eigenvalue changes can be computed numerically by overlapping the adjoint eigenfunction with the first-order global eigenmode correction, shown here for the first time. We confirm the prediction against a direct computation, showing that the eigenvalue drift due to a spanwise wavy base flow modification is of second order. Further analysis reveals that the second-order change in the eigenvalue arises through a resonance of the original (2-D) eigenmode with other unperturbed eigenmodes that have the same spanwise wavelength as the base flow modification. The eigenvalue drift due to each mode interaction is inversely proportional to the distance between the eigenvalues of the modes (which is similar to resonance), but also depends on mutual overlap of direct and adjoint eigenfunctions (which is similar to pseudoresonance). By this argument, and by calculating the most sensitive regions identified by our analysis, we explain why an in-phase actuation/modification is better than an out-of-phase actuation for control of wake flows by spanwise wavy suction and blowing. We also explain why wavelengths several times longer than the wake thickness are more efficient than short wavelengths.This work was supported by the European Research Council through Project ALORS 2590620.This is the accepted manuscript. The final version is available from CUP at http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9326225&fileId=S002211201400415

Level-3 Calorimetric Resolution available for the Level-1 and Level-2 CDF Triggers

As the Tevatron luminosity increases sophisticated selections are required to be efficient in selecting rare events among a very huge background. To cope with this problem, CDF has pushed the offline calorimeter algorithm reconstruction resolution up to Level 2 and, when possible, even up to Level 1, increasing efficiency and, at the same time, keeping under control the rates. The CDF Run II Level 2 calorimeter trigger is implemented in hardware and is based on a simple algorithm that was used in Run I. This system has worked well for Run II at low luminosity. As the Tevatron instantaneous luminosity increases, the limitation due to this simple algorithm starts to become clear: some of the most important jet and MET (Missing ET) related triggers have large growth terms in cross section at higher luminosity. In this paper, we present an upgrade of the Level 2 Calorimeter system which makes the calorimeter trigger tower information available directly to a CPU allowing more sophisticated algorithms to be implemented in software. Both Level 2 jets and MET can be made nearly equivalent to offline quality, thus significantly improving the performance and flexibility of the jet and MET related triggers. However in order to fully take advantage of the new L2 triggering capabilities having at Level 1 the same L2 MET resolution is necessary. The new Level-1 MET resolution is calculated by dedicated hardware. This paper describes the design, the hardware and software implementation and the performance of the upgraded calorimeter trigger system both at Level 2 and Level 1.Comment: 5 pages, 5 figures,34th International Conference on High Energy Physics, Philadelphia, 200

Three-dimensional flow instability in a lid-driven isosceles triangular cavity

Linear three-dimensional modal instability of steady laminar two-dimensional states developing in a lid-driven cavity of isosceles triangular cross-section is investigated theoretically and experimentally for the case in which the equal sides form a rectangular corner. An asymmetric steady two-dimensional motion is driven by the steady motion of one of the equal sides. If the side moves away from the rectangular corner, a stationary three-dimensional instability is found. If the motion is directed towards the corner, the instability is oscillatory. The respective critical Reynolds numbers are identified both theoretically and experimentally. The neutral curves pertinent to the two configurations and the properties of the respective leading eigenmodes are documented and analogies to instabilities in rectangular lid-driven cavities are discussed