NSUF 16-788: Study of deformation mechanisms of zirconium alloys under irradiation
In Pressurized Water Reactors, cladding tubes, made of zirconium alloys, are subjected to several mechanical loadings. Indeed the cladding tubes undergo irradiation creep due to the compressive hoop stress of the primary circuit and to the neutron flux. In order to predict and to take into account the dimensional changes of zirconium alloys under irradiation, a good understanding of the deformation mechanisms is needed. Theoretical mechanisms have been proposed in the literature to explain the irradiation creep deformation but only few experimental evidences exist. Most of these theoretical mechanisms involve a climb mechanism of dislocations under irradiation. Few experimental studies have been conducted on that subject at a microscopic scale and the mechanisms still need to be known to allow a better understanding of the in-reactor behavior of zirconium alloys. This project is part of a PhD work untitled: “Experimental study of deformation mechanisms of zirconium alloys under irradiation”. The goal of this work is to study the microstructure evolution of a specific zirconium alloy, the recrystallized Zircaloy-4 (Zy-4), under irradiation and to determine the microscopic deformation mechanisms at the origin of irradiation creep, which mainly involve dislocation climb. In-situ charged particles irradiations have been performed first without an applied stress. Electron irradiations have been conducted at high temperatures (400°C) using the EM7 High Voltage Electron Microscope at the CEA of Saclay (France). Pre-strained Zy-4 thin samples have been used to insure the presence of a or c+a-type dislocations and therefore simplify the observation of the deformation mechanisms. These electron irradiations have confirmed the involvement of a dislocation climb mechanism explaining the deformation of Zy-4 under irradiation. Indeed, the dislocations observed tend to become helical which is an experimental evidence of dislocation climb. The formation of dislocation loops have also been observed and analyzed. Ion irradiations have been performed at Jannus CSNSM (Orsay, France) and proof of dislocation climb, as wavy dislocations, have been observed. To obtain a better understanding of irradiation creep deformation mechanisms, irradiations with an applied stress are needed. Preliminary experiments were conducted at CSNSM with Zy-4 samples subjected to Zr ion irradiation and to a tensile test. The growth of dislocation loops, as well as the activation of glide and climb mechanisms, appear to be dependent of their orientation with respect to the applied stress. However, these experiments have been performed at room temperature. In-situ irradiation experiments at high temperature should now be performed with an applied stress and directly compared to the irradiation experiments performed without an applied stress. Therefore, the direct effect of the strain on the microscopic mechanisms could be studied and would allow better understanding of the deformation mechanisms due to the irradiation creep.
Due to the schedule planned for this final year thesis, it would be more convenient if the period of performance is between january and march 2017.
Additional Info
| Field | Value |
|---|---|
| Abstract | In Pressurized Water Reactors, cladding tubes, made of zirconium alloys, are subjected to several mechanical loadings. Indeed the cladding tubes undergo irradiation creep due to the compressive hoop stress of the primary circuit and to the neutron flux. In order to predict and to take into account the dimensional changes of zirconium alloys under irradiation, a good understanding of the deformation mechanisms is needed. Theoretical mechanisms have been proposed in the literature to explain the irradiation creep deformation but only few experimental evidences exist. Most of these theoretical mechanisms involve a climb mechanism of dislocations under irradiation. Few experimental studies have been conducted on that subject at a microscopic scale and the mechanisms still need to be known to allow a better understanding of the in-reactor behavior of zirconium alloys. This project is part of a PhD work untitled: “Experimental study of deformation mechanisms of zirconium alloys under irradiation”. The goal of this work is to study the microstructure evolution of a specific zirconium alloy, the recrystallized Zircaloy-4 (Zy-4), under irradiation and to determine the microscopic deformation mechanisms at the origin of irradiation creep, which mainly involve dislocation climb. In-situ charged particles irradiations have been performed first without an applied stress. Electron irradiations have been conducted at high temperatures (400°C) using the EM7 High Voltage Electron Microscope at the CEA of Saclay (France). Pre-strained Zy-4 thin samples have been used to insure the presence of a or c+a-type dislocations and therefore simplify the observation of the deformation mechanisms. These electron irradiations have confirmed the involvement of a dislocation climb mechanism explaining the deformation of Zy-4 under irradiation. Indeed, the dislocations observed tend to become helical which is an experimental evidence of dislocation climb. The formation of dislocation loops have also been observed and analyzed. Ion irradiations have been performed at Jannus CSNSM (Orsay, France) and proof of dislocation climb, as wavy dislocations, have been observed. To obtain a better understanding of irradiation creep deformation mechanisms, irradiations with an applied stress are needed. Preliminary experiments were conducted at CSNSM with Zy-4 samples subjected to Zr ion irradiation and to a tensile test. The growth of dislocation loops, as well as the activation of glide and climb mechanisms, appear to be dependent of their orientation with respect to the applied stress. However, these experiments have been performed at room temperature. In-situ irradiation experiments at high temperature should now be performed with an applied stress and directly compared to the irradiation experiments performed without an applied stress. Therefore, the direct effect of the strain on the microscopic mechanisms could be studied and would allow better understanding of the deformation mechanisms due to the irradiation creep. Due to the schedule planned for this final year thesis, it would be more convenient if the period of performance is between january and march 2017. |
| Award Announced Date | 2016-12-16T07:45:20.03 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | None |
| PI | Marine Gaumé |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 788 |