Ceramic Materials for Nuclear Energy Research and Applications: High Burnup Oxide Fuels
Sponsored by: TMS Extraction and Processing Division, TMS Structural Materials Division, TMS Light Metals Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Energy Committee, TMS: Nuclear Materials Committee
Program Organizers: Xian-Ming Bai, Virginia Polytechnic Institute and State University; Yongfeng Zhang, University of Wisconsin; Larry Aagesen, Idaho National Laboratory; Vincenzo Rondinella, Jrc-Ec
Wednesday 8:30 AM
March 17, 2021
Room: RM 51
Location: TMS2021 Virtual
Session Chair: Miaomiao Jin, Idaho National Laboratory; Karim Ahmed, Texas A&M University
8:30 AM Invited
Modeling of Pressure-driven Inter-granular Fracture in High Burnup Structure UO2 during LOCA Using A Phase-field Approach: Wen Jiang1; Larry Aagesen1; Kyle Gamble1; 1Idaho National Laboratory
UO2 has been widely used as nuclear fuel material for commercial light water reactors (LWRs). One of the current objectives of LWR operators is to extend current UO2 fuels to high burnups and ensure them to operate safely during accident conditions such as Loss of Coolant Accidents (LOCA). During a LOCA, it has been observed in experiments that the UO2 fuel can finely fragment and axially relocate within the rod resulting in the possibility of fuel dispersal upon cladding rupture. To understand the fragmentation mechanism, a phase field fracture model is developed to model the pressure-driven inter-granular fracture. The bubble pressure inside the bubble due to temperature transient is obtained by a phase field bubble pressure model. The simulation results will be used to assess whether the bubble pressure is sufficient to drive fracture and provide fundamental understanding of the fragmentation mechanism for high burnup structure.
9:00 AM
Multiscale Modeling of High Burn-up Structure (HBS) Formation and Evolution in UO2: Karim Ahmed1; Mohammed Abdoelatef1; Sudipta Biswas2; Larry Aagesen2; David Andersson3; 1Texas A&M University; 2INL; 3LANL
A multiphysics, multiscale model was developed to simulate the High burn up structure (HBS) formation in UO2. First, an atomistic model was established to accurately estimate the effective diffusion coefficient of Xe in UO2 talking into account different diffusion mechanisms. Then a mesoscale model was formulated to couple rate-theory and phase-field modeling techniques to simulate the concurrent evolution of defects and microstructure. The resultant model is able to account for the accumulation of point defects into bubbles and dislocation loops and the eventual transformation into the porous fine-grained HBS. The effects of temperature, bubble pressure, density and distribution of dislocation loops, grain and bubble sizes were thoroughly investigated. The consequence of the findings on gas swelling and release rates, fracture, and fragmentation will be discussed.
9:20 AM
A Thermo-mechanical Coupled Phase Field Dynamic Fracture Model and Its Application in UO2: Shuaifang Zhang1; Wen Jiang2; Michael Tonks1; 1University of Florida; 2Idaho National Laboratory
Fuel fragmentation has been paid a lot of attention in recent years, because fragmentation significantly impacts reactor safety during an accident. The phase field method has been developed as a powerful tool to capture fracture. In this talk, we present a thermo-mechanical phase field model of dynamic fracture that has been developed for fuel fragmentation. The model includes the impact of elastic anisotropy and has been validated using several benchmark simulations compared with other simulation and experimental results. After the verification and validation of this model, we then apply this model to simulate the crack behaviors of UO2, where we use the anisotropic elastic constants and adjust the fracture parameters to match the crack stress of UO2. Finally, we simulate fuel fragmentation with the impact of bubbles and grain boundaries.
9:40 AM Invited
Phase-field Modeling of Bubble Growth During High Burn-up Structure Formation in UO2: Sudipta Biswas1; Andrea Jokisaari1; Larry Aagesen1; 1Idaho National Laboratory
In UO2 fuel, regions exposed to high burn-up and low temperatures exhibit a fine-grained microstructure with large bubbles known as high burn-up structure (HBS). A phase-field model is developed to investigate the mechanisms facilitating the creation of such a structure. The model captures the formation of smaller grains due to defect accumulation overtime via recrystallization, employing a dislocation density based discrete nucleation algorithm. The model also accounts for existing fission gas bubbles and concurrently tracks the concentration of defects, such as vacancies and gas atoms, leading to further bubble growth. Additionally, it considers the role of recombination of defects, various diffusion mechanisms, and activation paths contributing towards coalescence of smaller bubbles into the larger ones. The model can generate realistic HBS structures, similar to what has been observed experimentally, that can be used to evaluate the effect of the structure on the thermo-mechanical properties and performance of the fuel.
10:10 AM Invited
Electron Microscopy Characterization of the Fuel-cladding Interaction in Annular Fast Reactor MOX: Fabiola Cappia1; Alex Winston1; Brandon Miller1; Jeffery Aguiar1; Boopathy Kombaiah1; Fei Teng1; Daniel Murray1; Jason Harp1; 1Idaho National Laboratory
Mixed Oxide (MOX) fuels for fast reactor are the reference fuel system for Sodium Fast Reactors (SFRs). In SFR MOX significant migration of fission products and fuel components occurs, resulting in fuel-cladding chemical interaction (FCCI). In this work, we present microscopy data focused on the FCCI layer in annular fast reactor MOX with HT-9 cladding at both medium and high burnup. In particular, the behavior of volatiles and the cladding components is studied. At intermediate burnup, accumulation of Cs, Te and I occurred in the outermost rim of the fuel pellet, where grain recrystallization has also been observed. The morphology and chemistry of the layer suggest a non-oxidative corrosion mechanism as principal cladding degradation phenomenon, with local onset of Cr oxidation within the nanocrystalline precipitates. At high burnup, the FCCI layer is composed mainly by Cs2MoO4. However, combinatorial analyses reveal that other non-stoichiometric phases are possible.
10:40 AM
Microstructural and Fission Products Analysis from Irradiated UO2 Fuel Using Atom Probe Tomography: Mukesh Bachhav1; Lingfeng He1; Brandon Miller1; Xiang Liu1; Fabiola Cappia1; Jian Gan1; 1Idaho National Laboratory
The distribution of solid and volatile fission product species has not been well characterized for UO2, however, because of the fine scale of precipitates and the possibility for dilute solid solutions fission product elements with the fuel alloy. Atom Probe Tomography (APT) provides a methodology to characterize spatial location and elemental composition of materials in three dimensions with near atomic-resolution high-resolution information is achieved through ion-by-ion field evaporation. Moreover, the development of shielded Focused Ion Beam instruments present unique opportunities presented for site-specific analysis for irradiated nuclear fuels using APT. The microstructure, composition, chemical and physical states of fission products, including metal and oxide precipitates and fission gas bubbles in irradiated ceramic fuels have been characterized using APT, Atomic-Resolution Scanning Transmission Electron Microscope equipped with energy dispersive X-ray spectroscopy system at Idaho National Laboratory. Findings of this work will be presented.