Delayed hydride cracking of nuclear fuel rod cladding tubes: experiments, modelling and numerical simulations of microstructural effects

 

Thomas THIBEAU^a,b, Pierrick FRANCOIS^a, Jean-Michel SCHERER^b, Quentin AUZOUX^c, Lionel GELEBART^d, Jacques BESSON^b

(thomas.thibeau@cea.fr)

 

^a Université Paris-Saclay, CEA, Service d'Etude des Matériaux Irradiés, 91191, Gif-sur-Yvette, France

^b Université PSL, Centre des Matériaux, 91003 Évry, France

^c Université Paris-Saclay, CEA, Service de recherche en Corrosion et Comportement des Matériaux, 91191, Gif-sur-Yvette, France

^d Université Paris-Saclay, CEA, Service de Recherche en Matériaux et Procédés Avancés, 91191, Gif-sur-Yvette, France

 

In France, used nuclear fuel rods are stored in pools (wet storage) in order to cool before being reprocessed or definitely stored. To save pool capacity, another method called dry storage is investigated. This method consists in cooling spent nuclear fuel assemblies inside dry casks. Due to the thermomechanical conditions undergone by the cladding tubes during dry storage, the delayed hydride cracking (DHC) phenomenon is studied. It is a 3-step failure mode which involves the hydrogen diffusion toward locations with the highest hydrostatic stress, hydride precipitation leading to embrittlement and ultimately crack initiation and propagation.

Previous investigation involving measurements [1], [2] showed that microstructure aspects such as crystallographic or morphologic texture are likely to influence macroscopic DHC aspects (fracture toughness, crack propagation rate). This study proposes a new experimental-numerical approach in order to assess the microstructure-related effects on the resistance to DHC. This approach enables to compare results and to fit simulation parameters from experimental measurements.

To begin with, the development of simulations using phase-field model (PFM) is in progress. The model is based on previous works such as simulations achieved by Simon [3] aiming at using PFM to simulate phase transformation involved by hydride precipitation. In addition to a single long-range order parameter used to describe the hydride orientation, a conserved parameter is used to represent the hydrogen concentration. This model aims at taking into account the differences in mechanical properties between the zirconium α-phase and hydrides and the influence of crystallographic texture and grain size on hydrides nucleation and growth. Simulations are conducted on zirconium alloys single crystal and polycrystals. The numerical resolution is achieved with the AMITEX code (https://amitexfftp.github.io/AMITEX/) developed at CEA using fast Fourier transform methods to solve the mechanical part and the chemical part of the model.

Furthermore, experimental electron backscatter diffraction (EBSD) observations are performed using a scanning electron microscope (SEM) equipped with a focused ion beam (FIB). While several studies in the literature such as observations carried out by Kumar et al. [4] have used EBSD to investigate the orientation relationship between hydrides and the zirconium matrix, the integration of FIB in this approach allows for EBSD measurements across multiple layers of a zirconium alloy specimen charged with hydrogen. Observations are conducted on notched and precracked specimens. 

 

 

 

 

[1]          Y. S. Kim, S. S. Kim, S. C. Kwon, K. S. Im, et Y. M. Cheong, « Anisotropic Threshold Stress Intensity Factor, KIH and Crack Growth Rate in Delayed Hydride Cracking of Zr-2.5Nb Pressure Tubes », Material and Mechanical Transactions, vol. 33A, p. 919-925, March 2002, doi: 10.1007/s11661-002-1024-2

[2]          P. Francois, T. Petit, Q. Auzoux, D. L. Boulch, I. Z. Nascimento, et J. Besson, « Assessing the Fracture Toughness of Zircaloy-4 Fuel Rod Cladding Tubes: Impact of Delayed Hydride Cracking », International Journal of Fracture: vol. 247 p. 51-72 ,1 December 2023. doi: 10.21203/rs.3.rs-3681084/v1.

[3]          P.-C. A. Simon et al., « Investigation of δ zirconium hydride morphology in a single crystal using quantitative phase field simulations supported by experiments », Journal of Nuclear Materials, vol. 557, p. 153303, December 2021, doi: 10.1016/j.jnucmat.2021.153303.

[4]          N. A. P. Kiran Kumar et J. A. Szpunar, « EBSD studies on microstructure and crystallographic orientation of δ-hydrides in Zircaloy-4, Zr–1% Nb and Zr–2.5% Nb », Materials Science and Engineering: vol. 528, p. 6366‑6374, August 2011, doi: 10.1016/j.msea.2011.05.022.

Souhaitez-vous présenter une affiche ?Zirconium alloys, Delayed hydride cracking, Texture, Phase field modelling, EBSD, FFTJJC 2025 - 25-26 nov 2025