Dislocation Loop Formation and Growth under In Situ Laser and/or Electron Irradiation

Vacancies and interstitial atoms are primary lattice (point) defects that cause observable microstructural changes, such as the formation of dislocation loops and voids in crystalline solids. These defects' diffusion properties determine the phase stability and environmental resistibility of macroscopic materials under ambient conditions. Although in situ methods have been proposed for measuring the diffusion energy of point defects, direct measurement has been limited. In this study, we propose an alternative in situ method to measure the activation energy for vacancy migration under laser irradiation using a pulsed laser beam from a laser-equipped high-voltage electron microscope (laser-HVEM). We made in situ observations that revealed the formation and growth of vacancy dislocation loops in an austenitic stainless steel during laser irradiation. These loops continued to grow when thermal annealing was performed after laser irradiation at the same temperature. We anticipate that laser-HVEM will provide a new method for investigating lattice defects

Caractérisation microstructurale et modélisation du durcissement des aciers austénitiques irradiés des structures internes des réacteurs à eau pressurisée

La structure internes de Réacteurs à Eau Pressurisée (REP) sont fabriquées en acier austénitique 304 hypertrempé pour le cloisonnement et 316 écroui pour la visserie. Ces structures internes sont soumises à un flux neutronique à une température comprise entre 280ʿC et 380ʿC, qui modifie leurs propriétés d'usage. Ces modifications des propriétés mécaniques sont la conséquence des modifications de la microstructure des matériaux sous irradiation, modification qui dépendent du flux, de la fluence et de la température d'irradiation. Nous avons observé en Microscopie Electronique en Transmission des aciers austénitiques 304H, 316E et 316TiE irradiés dans un réacteur à flux mixte (OSIRIS à 330ʿC à des doses comprises entre 0,8 dpa et 3,4dpa) et des échantillons irradiés dans un Réacteur à Neutrons Rapides (BOR-60) à la même température jusqu'à des doses de 40 dpa. De plus, nous disposons d'échantillons irradiés à 375ʿC dans un Réacteur à Neutrons Rapides (EBR-II) jusqu'à des doses de 10 dpa. On constate que les défauts d'irradiation sont essentiellement des boucles de dislocations de Frank fautées situées dans les plans {111} de l'austénite dont le vecteur de Burgers est de type [111]. La présence de cavités a été mise en évidence dans les aciers hypertrempés irradiés à 375ʿC. Nous avons modélisé l'évolution de la population de boucles d'irradiation et de cavités par une simulation de type "dynamique d'amas". L'ajustement des paramètres du modèle nous a permis de décrire quantitativement nos résultats expérimentaux. Cette description de la microstructure d'irradiation a été couplée à un modèle de durcissement par des boucles de Frank, qui nous a permis de décrire quantitativement le durcissement observé, pour une dose, un flux et une température donnée, sur les aciers 304 Hypertrempé, 316 Ecoui et 316 Ti Ecroui. La gamme de doses explorée va jusqu'à 90 dpa, représentative de la fin de vie de conception des réacteurs.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Tomographic atom probe characterization of the microstructure of a cold worked 316 austenitic stainless steel after neutron irradiation

International audienceFor the first time, chemical analyses using Atom Probe Tomography were performed on a bolt made of cold worked 316 austenitic stainless steel, extracted from the internal structures of a pressurized water reactor after 17 years of reactor service. The irradiation temperature of these samples was 633 K and the irradiation dose was estimated to 12 dpa (7.81 × 1025 neutrons.m−2, E > 1 MeV). The samples were analysed with a laser assisted tomographic atom probe. These analyses have shown that neutron irradiation has a strong effect on the intragranular distribution of solute atoms. A high number density (6 × 1023 m−3) of Ni–Si enriched and Cr–Fe depleted clusters was detected after irradiation. Mo and P segregations at the interfaces of these clusters were also observed. Finally, Si enriched atmospheres were seen

Tomographic atom probe characterization of the microstructure of a cold worked 316 austenitic stainless steel after neutron irradiation

International audienceFor the first time, chemical analyses using Atom Probe Tomography were performed on a bolt made of cold worked 316 austenitic stainless steel, extracted from the internal structures of a pressurized water reactor after 17 years of reactor service. The irradiation temperature of these samples was 633 K and the irradiation dose was estimated to 12 dpa (7.81 × 1025 neutrons.m−2, E > 1 MeV). The samples were analysed with a laser assisted tomographic atom probe. These analyses have shown that neutron irradiation has a strong effect on the intragranular distribution of solute atoms. A high number density (6 × 1023 m−3) of Ni–Si enriched and Cr–Fe depleted clusters was detected after irradiation. Mo and P segregations at the interfaces of these clusters were also observed. Finally, Si enriched atmospheres were seen

Lessons learned from baffle bolt replacements regarding irradiation-induced creep behaviour

An overall maintenance policy for managing ageing of PWR vessel internals, subject to high neutron fluence, was launched by EDF during the 90’s. It involves four main activities that are dependent on:− Safety Analysis, − R&D Program, − In-Service Inspection and/or Maintenance Program, − Metallurgical Examinations. The purpose of this paper is to analyze field data obtained from baffle to former bolts replacement operations using materials properties obtained from R&D programs. We show that following highly anticipative R&D, a comprehensive approach can be established to account for irradiation creep behavior of baffle bolts. The approach relies on (i) irradiation-creep law established by means of irradiated pressurized tubes for SA-304 and CW-316, (see presentation from J. Garnier in the conference),(ii) measurement of removal torques of baffle bolts recorded during their replacement, (iii) metallurgical examination of bolts, (iv) knowledge of dose distribution within the components and (v) modeling of the mechanical behaviour of the bolts. It is concluded that torque values measured during removal of baffle to former bolts can be explained by irradiation- induced creep experimental laws