Abstract
During normal in-service operation, the PWR fuel assemblies exhibit a macroscopic elongation. This dimensional change is the result of three different phenomena: thermal creep, irradiation-creep and irradiation growth which occurs in the absence of any applied stress. This last phenomenon, referred as stress-free growth, is related to irradiation-induced microstructural changes taking place in the hexagonal close packed grains and corresponding to an elongation along the basal plane and a shortening along the c-axis, the volume remaining constant (Fig 1). Under neutron irradiation, recrystallized Zr-based alloys undergo stress-free growth which accelerates for high irradiation doses (Fig 2). This acceleration is correlated to specific c-component vacancy dislocation loops.
Highlights
Q1: Coupling under irradiation between ‘stress-free’ growth and axial irradiation creep ? Hypothesis: c-loops are responsible for the growth breakaway
For the first time loops have been observed in Zr alloys after proton and Zr ion irradiations
Samples taken in the (TD, RD) plane of an intermediate product: TREX
Summary
Prediction of the macroscopic elongation of fuel assemblies under neutron irradiation. Hypothesis: c-loops are responsible for the growth breakaway. Q2: How macroscopic stress and in-service hydrogen pick-up could influence the growth acceleration?. For the first time loops have been observed in Zr alloys after proton and Zr ion irradiations. 11.5 dpa Nucleation starts between 4.1dpa and 5.5dpa Growth and nucleation continue with dose increasing. Evolution of loops density vs irradiation protons dose in Zircaloy-4 and M5® alloys. Large and faulted loops in consistent densities with increasing dose Fewer loops in M5® than in RXA Zy-4. Charged particles irradiations (mainly Protons) are representative of PWR operating conditions [1] P.Bossis et al, 15th ASTM, 2009 [2] D.Gilbon et al, 10th ASTM, 1994. Samples taken in the (TD, RD) plane of an intermediate product: TREX o Tube of ~11 mm thick o Transverse texture (0002) Pole figure
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