An experimental approach for the analytical study of secondary hydriding of fuel rods during a LOCA

Apou Martial Kpemou (1) , Marie-Christine Baietto (2) , Jean Desquines (1) , Tatiana Taurines (3) , A Ambard (4) , F Bourlier (5)

1 IRSN/PSN-RES/SEREX/LE2M - Laboratoire d'Expérimentation en Mécanique et Matériaux
2 LaMCoS - Laboratoire de Mécanique des Contacts et des Structures [Villeurbanne]
3 IRSN/PSN-RES/SEMIA/LEMC - Laboratoire d'étude et de modélisation du combustible
4 EDF R&D - EDF R&D
5 AREVA NP Lyon

Secondary hydriding may occur in nuclear fuel cladding materials exposed to steam at high temperature in Loss of Coolant Accident (LOCA) conditions. During a LOCA transient, the cladding may burst, and the steam ingress leads to the cladding inner surface oxidation in the vicinity of the burst balloon. A high hydrogen uptake can then occur near the burst position, and this can lead to strong hydrogen concentration in the cladding. Semi-integral devices were set up to experimentally reproduce LOCA transients and these semi-integral tests usually lead to hydrogen enriched bands, at some distance from burst opening, characterized by various techniques. The complex nature of these tests combined to the three-dimensional cladding geometry obtained after burst impedes the study of the various parameters influencing secondary hydriding. Burst opening size, gap size, oxidation duration and other parameters influences are characterized using a fully axisymmetric testing procedure reproducing LOCA conditions including cladding oxidation and final quench of the sample. A non-deformed cladding, opened on one-side and closed on the other one, is filled with pellets and exposed to steam at high temperature (1200 °C). An hydrogen gas release occurs as a result of the cladding oxidation process and a high hydrogen uptake by the cladding is observed in the pellet-cladding gap a few millimetres below the top of the pellet stack near the opening and where the thin internal oxide layer disappears. This procedure allows using analytical LOCA tests to study the influence of different parameters and can also contribute to validate numerical methods for the simulation of secondary hydriding. Some post-test analyses are performed on the cladding samples subjected to this procedure. Post-quench material microstructure including inner and outer oxide layer thickness axial profiles were characterized using metallography. Hot Vacuum Extraction (HVE) was used to measure hydrogen concentrations.

Domaines: Physique [physics]

Apou Martial Kpemou, Marie-Christine Baietto, Jean Desquines, Tatiana Taurines, A Ambard, et al.. An experimental approach for the analytical study of secondary hydriding of fuel rods during a LOCA. NuMat2022: The Nuclear Materials Conference, Oct 2022, Ghent, Belgium. ⟨irsn-04040328⟩