Publications
Nuclear Fuel Cycle (NFC) Technology and Policy Program
Modeling of Thermo-Mechanical and Irradiation Behavior of Metallic and Oxide Fuels for Sodium Fast Reactors
Aydın Karahan and Jacopo Buongiorno
MIT-NFC-TR-110 (August 2009)
Abstract
An engineering code to model the irradiation behavior of U-Zr and U-Pu-Zr metallic alloy fuel pins and UO₂-PuO₂ mixed oxide fuel pins in sodium cooled fast reactors was developed. The code was named the Fuel Engineering and Structural analysis Tool (FEAST). FEAST has several modules working in coupled form with an explicit numerical algorithm. These modules describe (1) Fission Gas Release and Swelling, (2) Fuel Chemistry and Restructuring, (3) Temperature Distribution, (4) Fuel Clad Chemical Interaction, (5) Fuel and Clad Mechanical Analysis and (6) Transient Creep-Fracture Model for the clad. Given the fuel pin geometry, composition and irradiation history, FEAST can analyze fuel and cladding thermo-mechanical behavior at both steady state and design-basis accident scenarios.
FEAST was written in FORTRAN-90 program language. The FEAST-METAL code mechanical analysis module implements the old Argonne National Laboratory (ANL)’s LIFE code algorithm. Fission gas release and swelling are modeled with the Korean GRSIS algorithm, which is based on detailed tracking of the fission gas bubbles within the metal fuel. Migration of the fuel constituents is modeled by means of the thermo-transport theory. Fuel Clad Chemical Interaction (FCCI) models were developed for steady-state and transient situations, based on precipitation kinetics. A transient intergranular creep-fracture model for the clad, which tracks the nucleation and growth of the cavities at the grain boundaries, was developed.
FEAST-METAL has been benchmarked against available EBR-II database for (steady state) and furnace tests (transients). The results show that the code is able to predict important phenomena such as cladding strain, fission gas release, clad wastage, clad failure time and axial fuel slug deformation, satisfactorily.
A similar code for oxide fuels, FEAST-OXIDE, was also developed. It adopts the OGRES model to describe fission gas release and swelling. However, the original OGRES model has been extended to include the effects of Joint Oxide Gain (JOG) formation on fission gas release and swelling. The fuel chemistry model includes diffusion models for radial actinide migration, cesium axial and radial migration, formation of the JOG, and variation of the oxygen to metal ratio. Fuel restructuring is also modeled, and includes the effects of porosity migration, irradiation-induced fuel densification and grain growth. The FEAST-OXIDE predictions has been compared to the available FFTF, EBR-II and JOYO databases, and the agreement between the code and data was found to be satisfactory.
Both metal and oxide versions of FEAST have some attractive characteristics with respect to other fuel codes found in the literature. The modeling capabilities of traditional codes were enhanced by adopting, to the extent possible, non-empirical mechanistic approaches that would provide confidence when the code is used to analyze fuel compositions, geometries and operating conditions that require extrapolation from the existing database. Specifically, FEAST-METAL uses (1) a fission gas release and swelling model that was specially developed for metallic fuels, (2) a fuel clad chemical interaction model that reflects the kinetics behavior for both steady state and transients, and (3) a mechanistic approach for the transient creep-fracture. The FEASTMETAL code is also capable of modeling the behavior of annular metal fuel pins with simultaneous internal and external cooling, a concept that is being explored to increase power density in sodium-cooled fast reactors. FEAST-OXIDE’s attractive featuers include (1) an advanced fission gas release and swelling model based on vacancy flow, (2) a detailed and mechanistic fuel chemistry model and its effect on thermal and mechanical performance, (3) a kinetics model for the clad wastage prediction, (4) a mechanistic approach for the transient creepfracture is adopted, and (5) account for the effects of fuel melting on the thermo-mechanical response of the fuel performance during severe transient overpower.
