Regular Article

Oxygen segregation in pre-hydrided Zircaloy-4 cladding during a simulated LOCA transient

¹ Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Centre d’Etudes de Cadarache, PSN-RES/SEREX/LE2M, BP3, 13115 Saint Paul-Lez-Durance Cedex, France
² INSA de Lyon, Laboratoire de Mécanique des Contacts et des Structures (LaMCoS), UMR 5259, 69621 Villeurbanne Cedex, France
³ École Centrale de Nantes, Institut de recherche en génie civil et mécanique (GEM), UMR 6183, 44321 Nantes, France
⁴ EDF-R&D, Les Renardières, département MMC, 77818 Moret sur Loing, France

^* e-mail: elodietorres@me.com

Received: 8 December 2015
Received in final form: 16 May 2017
Accepted: 8 August 2017
Published online: 29 September 2017

Abstract

Oxygen and hydrogen distributions are key elements influencing the residual ductility of zirconium-based nuclear fuel cladding during the quench phase following a Loss Of Coolant Accident (LOCA). During the high temperature oxidation, a complex partitioning of the alloying elements is observed. A finite-difference code for solving the oxygen diffusion equations has been developed by Institut de Radioprotection et de Sûreté Nucléaire to predict the oxygen profile within the samples. The comparison between the calculations and the experimental results in the mixed α+β region shows that the oxygen diffusion is not accurately predicted by the existing modeling. This work aims at determining the key parameters controlling the average oxygen profile within the sample in the two-phase regions at 1200 °C. High temperature steam oxidation tests interrupted by water quench were performed using pre-hydrided Zircaloy-4 samples. Experimental oxygen distribution was measured by Electron Probe Micro-Analysis (EPMA). The phase distributions within the cladding thickness, was measured using image analysis to determine the radial profile of α(O) phase fraction. It is further demonstrated and experimentally checked that the α-phase fraction in these regions follows a diffusion-like radial profile. A new phase fraction modeling is then proposed in the cladding metallic part during steam oxidation. The modeling results are compared to a large set of experiments including the influence of exposure duration and hydrogen content. Another key outcome from this modeling is that oxygen average profile is straightforward derived from the proposed modeling.