Radiation damage and its impact on corrosion in Zirconium-Niobium alloys
Notice bibliographique
Résumé
Zirconium alloys have been successfully used as fuel cladding and structural materials in fission reactors for decades, but the industry’s desire to employ high burnup fuels requires an improvement of resistance to in-reactor corrosion. It is therefore essential to understand the mechanisms of radiation-enhanced corrosion of zirconium alloys, and especially why Zr-Nb alloys show improved properties compared to Zircaloys. In order to achieve this goal, the MUZIC-3 (Mechanistic Understanding of Zirconium Corrosion) program was established; a wide collaboration between universities and industrial partners. As part of this program, this project used advanced electron microscopy techniques to investigate in-reactor corroded samples from the Canada Nuclear Laboratory and autoclave corroded samples from Westinghouse. The characterisation work used the (S)TEM as a primary tool, together with the analytical tools EDX and EELS. The in-reactor samples were Zr – 2.5 Nb samples corroded at 325 °C and 250 °C in the reactor core for 190 days and 2750 days. For comparison, samples corroded in the same primary loop but out of the reactor core, and hence without neutron radiation, have also been studied. In order to further study the mechanism of radiation damage in the metal matrix, in-situ heavy ion radiation in a TEM was carried out on the recrystallised Zr – 1.0Nb and Zr – 2.5Nb alloys provided by Westinghouse<sup>TM</sup>, and proton irradiation was carried out at Dalton Cumbrian Facility (DCF) on as-received Zr – 2.5Nb alloys from CNL. All the TEM samples in this project were made by Focused Ion Beam (FIB) at either the University of Oxford or the Materials Research Facility (MRF) at the Culham Science Park. The first section of results presented in this thesis is the characterisation of the metal matrix of the CNL Zr – 2.5Nb alloy. The shape, orientation and number density of radiation-induced Nb precipitates in the α-Zr grains in samples corroded under neutron radiation at 325 °C was analysed. The direct observation of fully coherent Nb nano-precipitates in the α-Zr metal matrix is reported for the first time. A model describing the formation and evolution of the Nb precipitates under neutron irradiation is suggested. The impact on the evolution of the β-Zr phase from the in-reactor conditions is also presented, and it is shown that decomposition from β-Zr to β-Nb is encouraged by neutron irradiation and in-reactor heating. The second section of the results discusses the mechanisms of radiation damage to the β-Nb SPPs in the metal matrix, as studied by in-situ heavy ion radiation. It was found that due to the combined effect of radiation-induced mixing and local diffusion of solute Nb atoms, the β-Nb SPPs stay very stable under irradiation up to 40 dpa and show very limited Nb redistribution between the SPPs and α-Zr metal matrix. Reasons for the remarkable stability of these Nb-rich phases under radiation are discussed. The characterisation of proton irradiated Zr – 2.5Nb samples is also presented. The results help to understand the mechanisms of radiation-induced Nb precipitation under a variety of conditions. The third section presents a study of the corrosion of the decomposed β-Zr regions in the oxide. This is a systematic study of the corrosion behaviour, including morphology changes, oxidation rates of the Nb in the β regions, redistribution of the Nb, and the relation with the formation of other microscopic features such as micro cracks. It is shown that the longer these β regions stay in the metal under neutron radiation, the more decomposed from β-Zr to β-Nb phase they become, and the slower that these regions are oxidised. With all these factors combined together, the reasons for the improved resistance of the Zr-Nb alloys to in-reactor corrosion is discussed.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».