A particular case of study in the field of nuclear fusion is the breeding blanket, a key component of the reactor responsible for the production of the required amount of tritium to fuel the fusion reaction. In the development of this technology, materials are proving to be one of the major bottlenecks, considering that the issues preventing its realization are the tritium permeation through steel structures and the corrosion promoted by the breeding materials. Ceramic coatings are proving to be highly efficient in countering these issues, and this thesis focuses on the characterization of two of the most promising candidates selected in the framework of the EUROfusion consortium: the deposition of an alumina (Al2O3) coating by means of Pulsed Laser Deposition (PLD), and the deposition of an Al2O3 coating by means of Atomic Layer Deposition (ALD). The final aim of this work is first of all to demonstrate the feasibility of the Al2O3-PLD coating as a barrier in fusion technology, showing its peculiar characteristics and unique protective properties. Given that the basic features of this material were already well-investigated before the beginning of this thesis, advanced experiments are designed in the framework of the EUROfusion consortium in order to test the coating in fusion relevant conditions. Several of these experiments are performed by third parties, given their degree of complexity (such as the test in the experimental nuclear reactor), while the outcomes are furtherly analysed and discussed by the author. In addition, it is demonstrated that the optimization of the deposited material is highly beneficial, thus a two-steps optimization is designed by the author. This resulted in drastic improvements in the protective performances of the coating, emphasising the importance of the quality of the material. The optimized coatings showed state-of-the-art permeation resistance to deuterium, even when irradiated, and optimal corrosion resistance to the breeding materials. In addition, Al2O3-PLD proves to have an excellent stability at high temperature and under thermal cycling, preserving also good tribo/mechanical properties, characteristics that are of critical importance when designing a protective barrier. Therefore, these tests show that the development of Al2O3-PLD III can give a substantial aid in enabling the breeding blanket technology. However, this deep study highlights also the limits of the PLD, such as the fact that it is a line-of-sight method. This is the reason why ALD is selected as an additional technique: to be used in a complementary fashion to PLD. The development of this technique is still at the early stages, thus the focus is the optimization of the coating, implementing innovative solutions to decrease the production of defects. Differently from PLD, this preliminary characterization is conducted mainly by the author, selecting methods available in the laboratory for fusion relevant investigations and designing quality check procedures. It is shown that ALD coatings possess promising features to be exploited as protective barrier, which will be improved with further optimization.
Un caso di studio nel campo della fusione nucleare è il breeding blanket, un componente chiave del reattore responsabile della produzione del trizio necessario per alimentare la reazione di fusione. Nello sviluppo di questa tecnologia, i materiali si stanno rivelando uno dei maggiori colli di bottiglia, considerando che i problemi che ne impediscono la realizzazione sono la permeazione del trizio attraverso le strutture in acciaio e la corrosione promossa dai materiali di breeding. I rivestimenti ceramici si stanno dimostrando efficaci nel contrastare questi problemi e questo lavoro di tesi si concentra sulla caratterizzazione di due dei candidati più promettenti selezionati nell'ambito del consorzio EUROfusion: la deposizione di un rivestimento di allumina (Al2O3) mediante Pulsed Laser Deposition (PLD), e la deposizione di un rivestimento di Al2O3 mediante Atomic Layer Deposition (ALD). Lo scopo finale di questo lavoro è innanzitutto dimostrare la fattibilità del rivestimento Al2O3-PLD come barriera nella tecnologia dei reattori a fusione, mostrandone le caratteristiche peculiari e le proprietà protettive uniche. Dato che le caratteristiche di base di questo materiale erano già ben studiate prima dell'inizio di questa tesi, sono stati progettati esperimenti avanzati nell'ambito del consorzio EUROfusion per testare il rivestimento in condizioni rilevanti per la fusione. Molti di questi esperimenti sono eseguiti da terze parti, dato il loro grado di complessità (come il test nel reattore nucleare sperimentale), mentre i risultati sono ulteriormente analizzati e discussi dall'autore. Inoltre, è stato dimostrato che l'ottimizzazione del materiale depositato è altamente vantaggiosa, pertanto l'autore ha progettato un processo di ottimizzazione in due fasi. Ciò ha comportato un drastico miglioramento delle prestazioni protettive del rivestimento, sottolineando l'importanza della qualità del materiale. I rivestimenti ottimizzati hanno mostrato una eccellente resistenza alla permeazione al deuterio, anche se irradiato, e un'ottima resistenza alla corrosione dei materiali di breeding. Inoltre, un rivestimento di Al2O3-PLD dimostra di possedere un'ottima stabilità alle alte temperature e ai ciclaggi termici, conservando anche buone proprietà tribo/meccaniche, caratteristiche che sono di fondamentale importanza nella progettazione di una barriera protettiva. Pertanto, questi test mostrano che lo sviluppo delle barriere di Al2O3-PLD di ultima generazione può fornire un aiuto sostanziale nello sviluppo della tecnologia del breeding blanket. Tuttavia, questo studio approfondito mette in luce anche i limiti della tecnologia PLD, come il fatto che sia un metodo “line of sight”. Questo è il motivo per cui la tecnologia ALD viene scelta come tecnica aggiuntiva, da utilizzare in modo complementare al PLD. Lo sviluppo di questa tecnica è ancora alle prime fasi, quindi il focus è l'ottimizzazione del rivestimento, implementando soluzioni innovative per diminuire la produzione di difetti. A differenza del PLD, questa caratterizzazione preliminare è condotta principalmente dall'autore, selezionando i metodi disponibili in laboratorio per le indagini rilevanti alla fusione e progettando procedure di controllo della qualità. È stato dimostrato che i rivestimenti ALD possiedono caratteristiche promettenti da sfruttare come barriera protettiva, che verranno migliorate con un'ulteriore ottimizzazione.
Amorphous alumina coatings for next generation nuclear systems
PALADINO, BORIS
2021/2022
Abstract
A particular case of study in the field of nuclear fusion is the breeding blanket, a key component of the reactor responsible for the production of the required amount of tritium to fuel the fusion reaction. In the development of this technology, materials are proving to be one of the major bottlenecks, considering that the issues preventing its realization are the tritium permeation through steel structures and the corrosion promoted by the breeding materials. Ceramic coatings are proving to be highly efficient in countering these issues, and this thesis focuses on the characterization of two of the most promising candidates selected in the framework of the EUROfusion consortium: the deposition of an alumina (Al2O3) coating by means of Pulsed Laser Deposition (PLD), and the deposition of an Al2O3 coating by means of Atomic Layer Deposition (ALD). The final aim of this work is first of all to demonstrate the feasibility of the Al2O3-PLD coating as a barrier in fusion technology, showing its peculiar characteristics and unique protective properties. Given that the basic features of this material were already well-investigated before the beginning of this thesis, advanced experiments are designed in the framework of the EUROfusion consortium in order to test the coating in fusion relevant conditions. Several of these experiments are performed by third parties, given their degree of complexity (such as the test in the experimental nuclear reactor), while the outcomes are furtherly analysed and discussed by the author. In addition, it is demonstrated that the optimization of the deposited material is highly beneficial, thus a two-steps optimization is designed by the author. This resulted in drastic improvements in the protective performances of the coating, emphasising the importance of the quality of the material. The optimized coatings showed state-of-the-art permeation resistance to deuterium, even when irradiated, and optimal corrosion resistance to the breeding materials. In addition, Al2O3-PLD proves to have an excellent stability at high temperature and under thermal cycling, preserving also good tribo/mechanical properties, characteristics that are of critical importance when designing a protective barrier. Therefore, these tests show that the development of Al2O3-PLD III can give a substantial aid in enabling the breeding blanket technology. However, this deep study highlights also the limits of the PLD, such as the fact that it is a line-of-sight method. This is the reason why ALD is selected as an additional technique: to be used in a complementary fashion to PLD. The development of this technique is still at the early stages, thus the focus is the optimization of the coating, implementing innovative solutions to decrease the production of defects. Differently from PLD, this preliminary characterization is conducted mainly by the author, selecting methods available in the laboratory for fusion relevant investigations and designing quality check procedures. It is shown that ALD coatings possess promising features to be exploited as protective barrier, which will be improved with further optimization.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/191921