DEVELOPMENT OF A PHASE FIELD MODEL OF HYDRIDE MORPHOLOGY IN ZIRCONIUM ALLOY NUCLEAR FUEL CLADDING
Open Access
- Author:
- Simon, Pierre Clement
- Graduate Program:
- Nuclear Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 17, 2017
- Committee Members:
- Arthur Thompson Motta, Thesis Advisor/Co-Advisor
Michael R. Tonks, Committee Member
Mary I Frecker, Committee Member - Keywords:
- Zirconium
Zirconium Hydrides
Phase Field Model
Grand Potential Model
Modeling
Nuclear Material
Nuclear Engineering
MOOSE
Verification
Validation
Nuclear Fuel Cladding - Abstract:
- Zirconium alloys are widely used in the nuclear industry as fuel cladding due to their particular properties. During normal operation conditions, hydrogen enters the cladding and forms brittle hydride precipitates. The effect of the presence of hydrides on the deformation behavior of the cladding largely depends on the orientation and the morphology of the hydrides. Because of the zirconium texture and the thermo-mechanical conditions, hydrides usually precipitate circumferentially in the cladding. However, temperature cycling and the application of additional stress can lead to hydride reorientation in the radial direction, which eases crack propagation through the cladding, and thus threatens the integrity of the fuel rod. In an effort to understand the mechanisms governing the orientation and the morphology of the hydrides, two different phase field models were developed using the Multi-physics Object Oriented Simulation Environment MOOSE. The first model was first proposed by Wheeler, Boettinger, and McFadden and is known as the WBM model. The second model, called the grand potential model, has the advantage of allowing the definition of the interfacial thickness independently of the bulk free energy of the different phases of the system. It thus allows the use of thicker interfaces, which means coarser mesh, making the simulations computationally less expensive. Because of the importance of the mechanical contributions in the nucleation and growth of hydride precipitates, both phase field models have then been coupled with elastic schemes. The first scheme, called the Voight-Taylor scheme (VTS), was shown to strongly overestimate the elastic free energy contribution at the interface, while the Khachaturya's scheme (KHS) performed better with just a small underestimation of the elastic free energy at the interface. In the project presented in this thesis, the multi-phase models simulated the alpha phase of the zirconium as well as the zeta, the gamma, and the delta phase of the hydrides. The models are dimensional, use the Gibbs free energy of formation of the different phases and the mechanical properties found in the literature. In this study, the phase field models have been carefully verified, meaning that their implementations have been successfully tested by comparing their results to widely accepted solutions. Once the models were applied to the zirconium hydride system, the first steps towards the validation of the code were promising. Simulated hydrides grew preferentially in the direction of the basal plane of the zirconium matrix, thus reproducing experimental observations.