Kinetics of UO2 oxidation in steam atmosphere

MELCOR 1.8.5 modeling aspects of fission product release, transport and deposition an assessment with recommendations.

“…UO 2 volatilization may be responsible for release of UO 3 as well as other less volatile species because of physical stripping of the fuel matrix containing the fission products. A number of more recently evolved release models consider the effect of fuel stoichiometry on the diffusion coefficient as well as the oxidizing/reducing potential of the environment [4,5,6,7]. The VICTORIA code considers a very large number of potential fission product species in a thermodynamic equilibrium approach.…”

Thermodynamic and kinetic modelling of fuel oxidation behaviour in operating defective fuel

“…The fuel oxidation model can be developed from available experimental information obtained from out-of-reactor and in-reactor investigations, and tested against limited post-irradiation examination data of spent defective fuel elements from commercial reactors [8][9][10][11][12][13][14][15][16][17]. The kinetics model must specifically account for multi-phase transport including interstitial oxygen diffusion in the solid and gas-phase transport of hydrogen and steam in the fuel cracks [18,19].…”

New modelling of the U–O–Zr phase diagram in the hyper-stoichiometric region and consequences for the fuel rod liquefaction in oxidising conditions

“…They indicate that the oxygen/metal ratio would be about 2.11. According to a second calculation [43,44] taking into account both oxygen surface exchange and volume diffusion, i.e. using a kinetic rather a thermodynamic approach, the oxygen/ metal ratio in fuel would be about 2.08 at 600 mm for a maximum temperature of 2600 K. For comparison, the deviations of fuel stoichiometry were about 2.14 for samples obtained from the molten core of the Three Mile Island Unit 2 (TMI-2) reactor [45] where the total pressure was higher than during the PHEBUS FP tests.…”