Microstructure effects on fracture strength of UO2 fuel pellets.

Abstract

Microstructure effects on the strength of U0 2 pellets have been investigated. The strength was measured at room temperature using a biaxial flexure technique in which thin disk specimens, sliced from U0 2 pellets, were fractured by ring loading in the specimen center. The strength of U0 2 was reduced, in all cases, by increase in porosity, grain size or pore size. Porosity and pore size had a significant influence, while grain size showed only a weak effect. The diameter of the maximun pore observed in the specimens was close to the critical flaw size calculated from the Griffith criterion. This indicates that the largest pore is the most important preexisting flaw which controls the pellet strength. The grain boundaries associated with the largest pore could play a role as a path for pore extension in the fracture process. The strength of U0 2 can be expressed bywhere u f is the fracture strength (MPa), PS the largest pore size (,urn), GS the mean grain size (,urn) and P the porosity (%). The equation demonstrated good predictive capabilities regarding strength of U0 2 pellets having wide variation in microstructure.

Crack tip plasticity in single crystal UO2: Atomistic simulations

“…The fracture behavior of UO 2 has been extensively studied since the 1960s [5][6][7][8][9][10][11][12]. Most of the previous work has focused on polycrystalline UO 2 (sintered) as it is easy to prepare and is the form being used in nuclear reactors.…”

Modelling of fine fragmentation and fission gas release of UO2 fuel in accident conditions

“…The best-estimate value for the local tensile strength of the HBS, σ cr hbs , is 21 MPa. This is about 30 % of the bulk tensile strength reported for unirradiated UO 2 at room temperature [147,[152][153][154][155]. The difference is partly related to the fact that σ cr hbs in our rupture criterion is applied without consideration of stress concentration effects of the spherical pores in the HBS.…”

Experimental characterization and modeling of UO 2 grain boundary cracking at high temperatures and high strain rates

“…The localization of pores, i.e., whether predominantly in the grains (intragranular) or at the grain boundaries (intergranular), but also the size and shape of pores (round or angular), have a strong impact on the material properties and the potential grain boundary cracking during mechanical tests [23][24][25]. In a recent experimental study, it was shown that very dense fuels (relative density >98%) with a small amount of intergranular pores tend to be more prone to grain boundary cracking during compressive creep experiments [16] (grain size being identical).…”