Assesment of potential swelling of Pressurized Water Reactor internals The GONDOLE experiment in Osiris reactor

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Extensive investigation of the mechanical properties of a Chooz A internal component

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Microstructural characterizations of austenitic stainless steels representative of PWR internals irradiated with ions from low to high doses and comparison to cluster dynamic simulations

International audienceThe French nuclear industry is looking into the extension of the operation time of pressurized water reactors (PWR) up to 60 years. The lower parts of the internals are composed of Solution Annealed (SA) 304 austenitic stainless steel plates and Cold Worked (CW) 316 stainless steel bolts. Due to their high exposition to irradiation it is expected to reach doses as high as 120 dpa after 60 years, at temperatures in the range of 300 to 370°C. The microstructures under ion irradiations of two 304 austenitic stainless steels grades that mainly differ in carbon content are investigated by Transmission Electron Microscopy (TEM). The evolution of radiation-induced defects as cavities, Frank loops and precipitates with the dose are studied as well as the influence of carbon. Ion irradiations from 5 to 100 dpa have been carried out at JANNuS-Saclay facility on using iron ions (10 MeV). To counterbalance the flux effect, irradiation temperature was set to 450°C.As observed in PWR internals, Frank loop density and size reach saturation at about 5 dpa. This validates the chosen shift of temperature. Major precipitation is observed in both 304 at high doses, however precipitates appears earlier and in higher concentration in the higher carbon content steel. Voids are present, and are relatively small in size and in low density considering the dose. As the dose increases the mean size and void density increase as well, with exception at high doses in 304L where a bimodal size distribution is observed. Carbon and precipitation seem to delay germination of cavities. In-situ irradiation up to 1.5 dpa were also performed at JANNuS-Orsay facility. It allows to investigate the evolution and creation of defects in the early moment of irradiation. Apparition of black dots and evolution of the dislocation network (Frank loops and perfect dislocations) are visible at the very beginning of irradiation. Finally, the evolution of the microstructure under irradiation with time (doses) and space (along the damage profile) is successfully modelled using Cluster Dynamic (CD) code CRESCENDO. Calculations along the profile damage show that surface and injected interstitials have an effect on the microstructure and confirm experimental observations. The effect of the surface is observable on cavities and Frank loops, on a large depth. Also, injected interstitials have an effect on both cavities and Frank loops. Microstructures as a function of the depth are explained based on the coupling between experiments and CD calculation

Investigation of ion irradiation defects microstructure and cavity swelling evolution in austenitic steels representative of PWR internals

International audienceThe lower core internals, notably made in Solution Annealed (SA) 304 austenitic stainless steels for plates, are structure supporting the fuel assemblies of Pressurized Water Reactors (PWR). They are exposed to high irradiation, inducing microstructural and microchemical changes with potential evolutions of macroscopic behaviours, as swelling, which is a macroscopic dimensional modification. This phenomenon has been associated to the formation and growth of cavities in Fast Breeder Reactors. Recently bubbles have been observed in PWR irradiated materials, but without macroscopic swelling. With the aim of the PWR operation time extension up to 60 years, doses as high as 120 dpa, at a temperature close to 300-370C should be reached and the evolution of the microstructure at high doses is a matter of concern.The evolution of the microstructure of two SA 304, with different carbon contents, has been investigated under Fe ion irradiation, from 5 dpa to 100 dpa at 450C. The radiation induced defects (cavities, Frank loops, precipitates) were investigated mainly by Transmission Electron Microscopy (TEM) and their evolution with dose will be described as well as the influence of carbon. It appears that swelling remains very low even at high doses. Parametrization of a cluster dynamics (CD) model has been done based on these experimental results. CD calculations were performed to simulate the evolution of defects with depth and results compared with observations along the damage profile on FIB samples. The use of ion irradiation to reproduce neutron irradiation microstructure will be discussed

Effects of injected interstitials and of the surface during 10 mev fe ions irradiation in 304 austenitic steels

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Tensile properties and deformation microstructure of highly neutron-irradiated 316 stainless steels at low and fast strain rate

International audiencePost-irradiation deformation behavior of solution-annealed (SA) and cold-worked (CW) 316 austenitic stainless steel irradiated to doses from 9 to 39 dpa is examined as a function of strain rate and irradiation conditions (neutron spectrum, temperature). Tensile properties are found to be significantly higher for lower irradiation temperature and for CW material, for similar irradiation levels. The effect of strain rate on tensile properties is shown to be weak in the range [10−8s−1; 10−4s−1]. TEM investigations after deformation for levels of plastic strain of about 1percent show on SA 316 the presence of deformation bands corresponding to one or even a mixture of twins, extended stacking faults, alpha-martensite islands and ε-martensite nanobands. Bundles of crisscrossing bands, found to be a composite of overlapping stacking faults, nanotwins and ε-martensite nanolayers, are observed at TEM foils edges near the grain boundaries with α′-martensite islands decorating these edges. Except observation of a slight decrease of the number of deformation bands in the specimen deformed at slower strain rate, no qualitative microstructural differences appear between specimens tested at slow and fast strain rates

Extensive investigation of the mechanical properties of a Chooz A internal component

International audienc