Integrated multi-physics design tool for fusion breeding blanket systems - development and validation

Das Brut-Blanket (BB) des DEMO-Reaktors ist ein anspruchsvolles System in gefährlicher Umgebung. Es unterliegt nukleartechnischen, thermisch-strukturellen sowie material- und sicherheitsrelevanten Anforderungen und Voraussetzungen, und seine komplexe Auslegung bedingt den Einsatz hochentwickelter multiphysikalischer Simulationstools. Diese Tools müssen die gleichzeitige Durchführung verschiedener Analysen erlauben. Drei dieser Analyseverfahren, nämlich das nukleare, das thermofluiddynamische und das thermomechanische Verfahren, können priorisiert und als vorbereitend für die Untersuchung aller weiteren Fragen im Zusammenhang mit dem Brut-Blanket betrachtet werden. Diese Dissertation schlägt einen die drei Säulen der Brut-Blanket-Auslegung (Neutronik, Thermohydraulik und Thermomechanik) umfassenden multiphysikalischen Ansatz vor. Zur Gewährleistung einer gesamtheitlichen Beurteilung der volumetrischen Wärmelasten, der thermischen Leistungen von Kühlmittel und Strukturmaterial sowie der Spannungs- und Verformungszustände müssen die entsprechenden Analysen im Verbund durchgeführt werden. Die Strategie zur Bewältigung dieser Herausforderung besteht in der Entwicklung eines CAD-zentrierten und lose gekoppelten Verfahrens für die Auslegung des Brut-Blankets mit Hilfe der Teilmodellierungstechnik MAIA (Multi-physics Approach for Integrated Analysis). Die Architektur von MAIA basiert auf der Verwendung validierter Codes und der Minimierung der Anzahl dieser Codes. Das Verfahren gliedert sich in zehn Hauptschritte, angefangen mit der Umwandlung des generischen CAD-Modells in ein für die Neutronen-/Photonentransportanalyse geeignetes Format, der kerntechnischen Analyse zur Beurteilung der volumetrischen Erwärmung und der Beurteilung der Temperatur- und Geschwindigkeitsfelder innerhalb von Kühlmittel und Strukturmaterial über die Bewertung der Verschiebungs-, Verformungs- und Spannungsfelder, die quantitative Bewertung der Erzeugung von Stickstoffisotopen durch Sauerstoffaktivierung des Wasser bis hin zur Berechnung der Konzentrationsverteilung unter Berücksichtigung der Auswirkungen des passiven konvektiven Transports. Allen Schritten gemeinsam sind die geometrischen Details und die Übereinstimmung zwischen Input- und Output-Parametern. Das neue MAIA-Verfahren unterscheidet sich vom konventionellen Kopplungsansatz in drei wesentlichen Aspekten: 1. Modelle und Lasten werden nicht homogenisiert. 2. Lastgradienten können mit hoher Auflösung in drei Richtungen für alle relevanten Analysen ohne übermäßigen Rechenaufwand erfasst werden. 3. Die Übereinstimmung zwischen den drei Analyseverfahren und die Kongruenz zwischen Inputs und Outputs wird gewährleistet. Der durch die CAD-zentrierte Funktion des MAIA-Verfahrens erforderliche Rechenaufwand bedingt allerdings die Darstellung von Teilen des Brut-Blankets und damit die Definition und Validierung von Randbedingungen für jede durchgeführte Berechnung. In Bezug auf die kerntechnische Analyse hat sich gezeigt, dass die relevanten Reflexions- und Weißzustände in poloidaler bzw. toroidaler Richtung zusammen mit dem Vorhandensein des Vakuumbehälters und der Definition lokaler Neutronen- und Photonenquellen zu einer Diskrepanz von -0,48 % in Bezug auf die aufgenommene Leistung zwischen DEMO-Reaktor und lokalen (z.B. Scheiben-)Modellen führen. Die neutronenphysikalischen Symmetriebedingungen gelten für das gesamte Modul einschließlich der Scheiben in der Nähe der Caps. Es wurde eine Sensitivitätsanalyse im Hinblick auf die Winkelverteilung der lokalen Neutronen- und Photonenquelle durchgeführt, die in 10 Cosinus-Bins die optimale Diskretisierung in Bezug auf den Kompromiss zwischen der Genauigkeit der erhaltenen Ergebnisse und den Ergebnissen des Referenzmodells und dem entsprechenden Rechenaufwand angibt. Bei der Analyse der thermohydraulischen Randbedingungen wurde festgestellt, dass die Beeinflussung der Temperaturverteilung durch die Abweichung der Massenströme (zwischen ~-1,3 % und ~0,6 %) und die Leistungsdichteschwankungen (bis zu ~6 % in den benachbarten Bereichen) weniger als ±2,4 % beträgt. Dies belegt die Anwendbarkeit der poloidalen Symmetriebedingungen. Im Verlauf der thermomechanischen Analysen wurden die Randbedingungen (d.h. radiale und toroidale Verschiebungen, die an den Knoten auf der Rückseite der hinteren Stützstruktur in toroidaler und poloidaler Richtung verhindert werden, Symmetrie an der unteren sowie generalisierter ebener Verformungszustand an der oberen Schnittfläche) bestimmt, die zu einer Diskrepanz in Bezug auf die Verschiebung im Teilmodell zwischen -6 % und 4 % und einer konservativen Bewertung der primären und sekundären Membran- und Biegespannungen führen. Darüber hinaus wurden die Auswirkungen der Temperaturschwankungen untersucht.Dabei zeigten sich Schwankungen der Gesamtverformung zwischen -0,3 % und 1,7 %, Schwankungen der äquivalenten Membranspannung von bis zu 15 % und Schwankungen der äquivalenten Biegespannung zwischen -7 % und 5 %. Das MAIA-Verfahren wurde anschließend zur Bewertung diverser Auswirkungen auf die Auslegung des Brut-Blankets herangezogen. Dabei wurden einige Kritikpunkte offenbar. Insbesondere zeigen die strömungsdynamischen Ergebnisse Überschreitungen der Grenztemperatur. Hierfür konnten keine geeigneten Konstruktionslösungen gefunden werden. Diese Nichteinhaltung der thermohydraulischen Anforderungen führt darüber hinaus zu sehr hohen, die Segmentstabilität möglicherweise gefährdenden Werten der von-Mises-Vergleichsspannungen. Im Hinblick auf das oben Gesagte kann das MAIA-Verfahren als Referenztool für die Auslegung des Brut-Blankets verwendet werden. Darüber hinaus hat das Verfahren die Möglichkeit aufgezeigt, sowohl wichtige zur Bestimmung der zulässigen Spannung und zur Erfüllung der Auslegungskriterien erforderliche Variablen wie den Neutronenfluss und die Temperatur als auch Primär- und Sekundärspannungen lokal abzubilden. Zur weiteren Veranschaulichung der Vielseitigkeit und Anpassungsfähigkeit des MAIA-Verfahrens wurde das Problem der Wasseraktivierung innerhalb des Blanket Primary Heat Transfer Systems (PHTS) untersucht. Mit MAIA konnten die Auswirkungen der Strömung auf die Stickstoffkonzentration berücksichtigt und nützliche Informationen für die Entwicklung der Brut-Blanket-Auslegung und des PHTS geliefert werden

INTEGRATED MULTI-PHYSICS DESIGN TOOL FOR FUSION BREEDING BLANKET SYSTEMS - DEVELOPMENT AND VALIDATION

Il Breeding Blanket (BB) del reattore DEMO rappresenta un sistema complesso in un ambiente pericoloso. Infatti, esso deve soddisfare diversi requisiti e vincoli ingegneristici sia di tipo nucleare, termo-strutturale che di sicurezza. Per questi motivi, è necessaria una progettazione omnicomprensiva che preveda l'applicazione di strumenti avanzati di simulazione basati su approcci multi-fisici. Questi strumenti devono eseguire simultaneamente diversi tipi di analisi. Tre di esse possono essere considerate prioritarie e propedeutiche per lo studio di tutti gli altri fenomeni riguardanti il BB, vale a dire l´analisi nucleare, termo-fluidodinamica e strutturale. In questa tesi, è proposto un innovativo approccio multi-fisico che copre i tre pilastri principali su cui è basato il progetto del BB (la neutronica, la termoidraulica e la termo-meccanica). Queste analisi devono essere condotte in maniera integrata, consentendo una valutazione olistica dei carichi volumetrici di potenza, delle prestazioni termiche sia del fluido di raffreddamento che delle strutture, nonché dei campi di tensione e deformazione. La strategia seguita per il conseguimento di questa sfida consiste nella creazione di una procedura “CAD-centric” e “loosely-coupled” (debolmente accoppiata) per la progettazione dei concetti di BB utilizzando una tecnica di analisi basata su sotto-modelli. Questa procedura prende il nome di Multi-physics Approach for Integrated Analysis (MAIA). Essa basa la sua architettura sull'uso di codici validati e sulla minimizzazione del loro numero. In particolare, MAIA è articolata in 10 fasi principali che vanno dalla creazione di un modello per le analisi nucleari generato dalla decomposizione in geometrie semplici di un generico CAD alla valutazione della potenza volumetrica, dal calcolo dei campi di temperatura e velocità nella struttura e nel refrigerante alla valutazione dei campi di spostamento, deformazione e stress, dalla stima dei tassi di produzione degli isotopi dell´azoto prodotti dall'attivazione dell'ossigeno presente nell'acqua al calcolo della loro distribuzione spaziale di concentrazione tenendo conto degli effetti del trasporto convettivo. Tutti i vari passaggi condividono gli stessi dettagli geometrici. In particolare, MAIA differisce dagli approcci convenzionali usati nell´accoppiamento multi-fisico su tre aspetti chiave. Innanzitutto, non introduce omogeneizzazioni dei modelli e dei carichi. In secondo luogo, MAIA permette di determinare, con un’alta risoluzione spaziale, i gradienti dei carichi per tutte le analisi coinvolte senza richiedere sforzi computazionali proibitivi. In terzo luogo, MAIA permette di mantenere la coerenza tra le tre analisi garantendo la congruenza tra gli input e gli output. Tuttavia, l´onere computazionale richiesto dall´approccio CAD-centric, su cui si basa la procedura MAIA, non permette di rappresentare il BB nel suo complesso ma solo alcune sue porzioni (una slice, per esempio). Ciò impone la definizione e, conseguentemente, la validazione di opportune condizioni al contorno per ogni sotto-modello utilizzato e per ogni analisi eseguita. A tal proposito, per quanto riguarda le analisi nucleari, le condizioni al contorno utilizzate nel modello locale della slice sono: definizione di una sorgente locale neutronica/fotonica per tener in conto l´effetto albedo dell´intero reattore, rappresentazione del Vacuum Vessel (VV) per simulare il back scattering verso il BB, e l´applicazione di condizioni di riflessione (“mirror”, specchio/simmetria, nella direzione poloidale e “white”, riflessione isotropica, in quella toroidale) per simulare la presenza delle slice adiacenti a quella analizzata. I risultati ottenuti mostrano una variazione della potenza depositata del -0.48 % tra il modello di riferimento DEMO e quello locale (slice). Inoltre, è stata eseguita un'analisi di sensibilità sulla distribuzione angolare della sorgente neutronica/fotonica locale determinando una discretizzazione ottimale in 10 suddivisioni poloidali. Questa suddivisione rappresenta un buon compromesso sia in termini di fedeltà dei risultati ottenuti, rispetto a quelli del modello di riferimento (DEMO), che di minimizzazione dell´onere computazionale. Per quanto riguarda l'analisi delle condizioni al contorno termo-idrauliche usate nel modello locale della slice, è stata applicata una condizione di simmetria termica poloidale. Assumendo una variazione delle portate comprese tra ~ -1.3% e ~ 0.6% e una fluttuazione della densità di potenza fino a ~ 6% tra slice vicine, è stata ottenuta una variazione della distribuzione delle temperature del ± 2.4% dimostrando, quindi, l'applicabilità di tali condizioni. Per quanto riguarda le analisi termo-meccaniche, le condizioni al contorno identificate per il modello locale della slice sono: simmetria sul piano inferiore della slice, Generalised Plane Strain su quello superiore e spostamenti radiali e toroidali impediti ai nodi che giacciono nella parte posteriore della back supporting structure lungo la direzione toroidale e poloidale. Queste condizioni, applicate al sotto-modello, producono una variazione compresa tra il -6% e il 4% tra gli spostamenti calcolati nella slice e quelli nel modello di riferimento DEMO, nonché una stima conservativa delle tensioni primarie e secondarie sia di membrana che di flessione. Inoltre, è stato anche studiato l'impatto della variazione (± 2.4%) di temperatura dimostrando che le fluttuazioni sulle deformazioni totale sono comprese tra il -0.3% e l’1.7%, fino a un massimo del 15% sulle tensioni equivalenti di membrana e tra il -7% e il 5% su quelle di flessione. Infine, la procedura MAIA è stata utilizzata per valutare l'impatto sul design del BB. La sua applicazione ha dimostrato la presenza di alcune criticità nel progetto. In particolare, i risultati fluidodinamici mostrano una violazione dei limiti di temperatura che non sono stati risolti introducendo soluzioni progettuali adeguate. Inoltre, queste violazioni producono, a loro volta, valori molto intensi delle tensioni equivalenti di Von Mises che potrebbero indicare un pericolo per l'integrità strutturale del BB. L´applicazione di MAIA al design del BB a permesso di dimostrare il valore aggiunto di questa procedura la quale potrebbe diventare uno strumento fondamentale e di riferimento per la progettazione del BB. Inoltre, la procedura MAIA ha permesso di mappare localmente variabili importanti come flussi neutronici e temperature, nonché le tensioni primarie e secondarie che sono utilizzate per la determinazione delle tensioni ammissibili applicate per la verifica dei criteri di progettazione. Al fine di dimostrare ulteriormente la versatilità e l'adattabilità della procedura MAIA, è stato studiato il problema di attivazione dell'acqua del sistema di trasferimento di calore primario (Primary Heat Transfer System, PHTS). Utilizzando la procedura MAIA, è stato possibile prendere in considerazione gli effetti dell´efflusso sulla concentrazione degli isotopi dell´azoto e fornire informazioni utili per lo sviluppo sia del design del BB che del suo PHTS.The Breeding Blanket (BB) of the DEMO reactor represents a harsh system in a dangerous environment. It has to satisfy engineering requirements and constraints that are of nuclear, thermo-structural, material and safety kind. For these reasons, the application of advanced simulation tools, based on a multi-physics approach, is required for its comprehensive design. These tools have to simultaneously perform different kind of analyses among which three, and namely nuclear, thermofluid-dynamic and thermo-mechanical, can be prioritized and considered as propaedeutic for the investigation of all the other issues related to the BB. In this dissertation, a multi-physic approach, covering the three pillars of the BB design (the neutronics, thermal-hydraulics and thermo-mechanics), is proposed. These analyses have to be conducted in a strongly integrated way, allowing a holistic assessment of volumetric heat loads, thermal performances of coolant and structures as well as their stress and deformation states. The strategy, followed for the achievement of this challenge, consists of creating a CAD-centric and loosely-coupled procedure for the BB concepts design adopting a sub-modelling technique, named Multi-physics Approach for Integrated Analysis (MAIA). The MAIA procedure bases its architecture on the use of validated codes and on the minimisation of their number. It is articulated in 10 main steps that go from the decomposition of generic CAD in a format suitable for neutron/photon transport analysis to the nuclear analysis for the assessment of volumetric heating, from the assessment of temperature and velocity fields within coolant and structure to the evaluation of their displacement, deformation and stress fields, from the evaluation of nitrogen isotopes production rates from water oxygen activation to the calculation of their concentration spatial distribution taking into account the effects of passive convective transport. All the steps share the same geometry details and the consistency between input and output parameters. The new MAIA procedure differs from the conventional coupling approach with respect to three key aspects. First, it does not introduce homogenisations of models and loads. Second, MAIA can capture load gradients at high resolution in the three directions for all the analysis involved without requiring prohibitive computational efforts. And third, MAIA keeps the consistency between the three analyses maintaining the congruence between inputs and outputs. However, the computational effort required by the CAD-centric feature of MAIA procedure imposes the representation of BB portions and, therefore, the definition and validation of boundary conditions for each performed calculation. Regarding the nuclear analysis, it has been found that the set of reflecting and white conditions in the poloidal and toroidal directions, respectively, together with the presence of Vacuum Vessel (VV) and the definition of local neutron and photon source, produces a mismatch of -0.48 % in terms of power deposition between the DEMO and the local (e.g. slice) models. It has been demonstrated that the neutronic symmetry conditions are valid in the entire module up to the last slices nearby the caps. Furthermore, a sensitivity analysis on the angular distribution of local neutron and photon source has been performed indicating in 10 cosine bins the optimal discretisation choice in terms of compromise between the fidelity of the results obtained respect to those of the reference model and the relevant computational effort. Concerning the analysis of thermal-hydraulic boundary conditions, it has been found that the variation on mass flow rates (comprised between the ~-1.3 % and the ~0.6 %) as well as power density fluctuation (up to the ~6 % in the neighbouring domains) affect the temperature distribution for less than ±2.4 % demonstrating the applicability of poloidal symmetry conditions. As far as the thermo-mechanical analyses are concerned, it has been identified the set of boundary conditions (radial and toroidal displacements prevented to the nodes lying in the rear of the back supporting structure along the toroidal and poloidal direction, symmetry at the lower cut surface and Generalised Plane Strain to the top one) that produce a discrepancy in terms of displacement in the sub-model comprised between the -6 % and the 4 % as well as a conservative assessment of membrane and bending stresses both for primary and secondary stresses. The impact of the temperature variation has also been investigated showing that the fluctuations on total deformation are comprised between -0.3 % and the 1.7 %, on equivalent membrane stress up to 15 % while on equivalent bending stress between the -7 % and the 5 %. As a proof-of-concept, the MAIA procedure has been then used to evaluate the impact on the BB design, demonstrating that some criticalities are present in the design. In particular, the fluid-dynamic results show a violation of the temperature requirement limits that have not been solved introducing proper design solutions. Furthermore, these violations of thermal-hydraulic requirements produce very intense values of Von Mises equivalent stresses that could jeopardize the structural integrity of the segment box. This demonstrates that MAIA procedure can become the reference tool for the design of the BB. Moreover, the MAIA procedure has proven the possibility to locally map important variables such as the neutron flux and the temperature as well as the primary and secondary stress that are used for the determination of the allowable stress and applied for compering with design criteria. In order to further demonstrate the versatility and adaptability of the MAIA procedure, the water activation issue occurring within the blanket Primary Heat Transfer System (PHTS) has been studied. Using MAIA procedure, it has been possible to take into account the effects of the flow on the nitrogen concentration and to provide useful information for the development of both BB design and its PHTS

Pre-commercial procurement and the marketing of innovation: a new innovation policy instrument or “old wine in new bottles”?

We analyse the peculiarities of pre-commercial procurement (PCP) within the EU innovation policy kit, interpreting it as a risk-shifting mechanism. While most studies assume the point of view of the public procurer, we take the suppliers’ one, with a focus on SMEs. We conclude that PCP, operating in the phase of the specification of technical requirements, has the peculiar role of favouring a better match between supply and demand as for innovative goods and can allow exploiting the competitive advantages that SMEs display in the early phases of the technological process, if interpreted as an innovation-leaking process

Tax policy response to market changes: the case of the gaming services sector

Beginning with the 1990’s, the gaming services sector has undergone several changes that have induced governments to review gambling taxes. We examine the economic rationale behind actual and prospected reforms, analysing the effects of gambling taxes on profits and extending existing industrial organisation results on the effects of cost changes in oligopolistic industries to different types of taxation instrument

Game of skill or game of luck? Motivations for gambling

The paper analyses the differences in gambling motivations of skill and luck gamblers based on the answers to a questionnaire distributed to students from the University of Pisa (Italy). We find that the probability of playing skill rather than luck games is positively correlated to being a male, to the socialization motive and to having a planning attitude and an interest in socializing. Instead, findings show that it is negatively correlated to the money motive, the perceived risk of losing social esteem, and age. Results are then applied to marketing strategies and public policies, with particular attention to the online environment

A comparative study of student reading and book buying habits

The objective of this study is to analyze the main aspects of reading habits and book purchasing behavior of university students in Zadar, Croatia, Pisa, Italy and Nanking, China. The authors will present a theorethical framework and the outcomes of a pilot study conducted comparatively in Pisa, Italy, Zadar, Croatia, and Nankig, China. The first part of the paper will discuss the theorethical framework based on the literature review of research papers published mainly in 2013 and 2014. The second part will present the results of a comparative study of university students' habits in book buying and reading in Pisa, Italy (the total of 55.000 students, a sample of 561 students, Zadar, Croatia (the total 5.500 students, a sample of 193 students) and Nanking, China (the total 30.000 students, a sample of 350 students). The main research questions are: - What are the books’ main rivals in occupying the leisure time of university students? - Who influenced the development of the students’ reading habits? - How much time do students spend reading online and on what devices? - What influences the students’ selection and the ultimate decision to purchase a book? - How do students acquire books for leisure reading? - How do student reading and book buying habits differ between the three universities in Italy, Croatia and China

Le banche di fronte alla sfida del Social Banking

Social Media represent a current and relevant trend for the banking sector: their use in support of or in substitution of traditional channels influences the way the offer of financial services is communicated and the management of stakeholder and client relationships. Therefore, it is increasingly important for financial institutions to understand and track Social Media interactions, especially during a time where banks are trying to gain more trust and achieve a closer social intimacy with clients after recent known events. This study has two aims: the first one is to analyse the content that banks and users share on two of the most popular social media platforms, and finally evaluate the role of digital channels in new business models of financial institutions. To reach these objectives, the study researched the interactions on Facebook and Twitter of 4 major banks, totalling 11.500 posts during 18 moths. The data, analysed through content analysis, highlights similarities and differences in the use of social media and illustrates how these new digital channels can contribute towards the development of client-bank relationships and, more broadly, to creating value

Communicating CSR: A selective empirical review of theories and methods. Work in progress

In this paper we provide an empirical analysis of the literature about Corporate Social Responsibility Communication (CSRC). Given the increasing amount of research related to this topic, a diverse set of theories, methods, and empirical findings coexist in the literature. Therefore, we have collected and analyzed CSRC papers in order to highlight which theoretical and methodological approaches have been used by scholars in the field, when dealing with empirical research. We believe that it is necessary to sum up this amount of research with the purpose of deriving insights about the current status of research and its possible future developments