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

Abstract

Abstract. Oxygen and hydrogen distributions are key elements influencing the residual ductility of zirconiumbased 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 a+b 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 a(O) phase fraction. It is further demonstrated and experimentally checked that the a-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.

Revisiting weight-gain correlations for as-fabricated Zircaloy-4 cladding tubes during steam oxidation

“…Similarly, Torres [TOR17] and Guilbert [GUI16] contributed to show that this solubility limit is not significantly influenced by hydrogen content up to 1000 wppm.…”

“…) . Torres [TOR17] has shown that average hydrogen contents up to 400 wppm had limited influence on this solubility limit, and Guilbert [GUI16] extended this conclusion for temperatures ranging between 1000 and 1200°C. At higher hydrogen contents, an influence of hydrogen content is expected as shown by Guilbert [GUI16].…”