Abstract
Hydrogen and oxygen are key elements influencing the embrittlement of zirconium-based nuclear fuel cladding during the quench phase following a Loss Of Coolant Accident (LOCA). The understanding of the mechanisms influencing the motion of these two chemical elements in the metal is required to fully describe the material embrittlement. High temperature steam oxidation tests were performed on pre-hydrided Zircaloy-4 samples with hydrogen contents ranging between 11 and 400 wppm prior to LOCA transient. Thanks to the use of both Electron Probe Micro-Analysis (EPMA) and Elastic Recoil Detection Analysis (μ-ERDA), the chemical elements partitioning has been systematically quantified inside the prior-β phase. Image analysis and metallographic examinations were combined to provide an average oxygen profile as well as hydrogen profile within the cladding thickness after LOCA transient. The measured hydrogen profile is far from homogeneous. Experimental distributions are compared to those predicted numerically using calculations derived from a finite difference thermo-diffusion code (DIFFOX) developed at IRSN.
Highlights
During a Loss Of Coolant Accident (LOCA) transient, the fuel cladding tubes are subjected to high temperature steam oxidation before core reflooding
This study aims at determining oxygen and hydrogen concentrations in cladding materials after a LOCA transient
During the high temperature oxidation, some strong partitioning of the chemical elements occurs within the thickness of the cladding tube due to the oxygen diffusion and the associated progressive transformation of the β-phase into an oxygen stabilized α(O) layer [6, 7]
Summary
During a LOCA transient, the fuel cladding tubes are subjected to high temperature steam oxidation before core reflooding. During this type of accident, metallurgical evolutions due to α-β phase transformations and partitioning of oxygen/hydrogen and of the main alloying elements is observed in the material. These phenomena have a strong influence on the material mechanical properties [1]. Most of the hydrogen moves towards the β-phase and is expected to remain in the prior β-phase after quenching [1, 2, 3]. The understanding of the mechanisms influencing the motion of these two chemical elements is required to fully describe the post-quenched embrittlement
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