Modelling of Defect Structure Evolution in Irradiated UO2 Fuel in the MFPR Code
M.S. Veshchunov1, V.D. Ozrin1, V.E. Shestak1, V.I. Tarasov1, R. Dubourg2, G. Nicaise2. 2004, International Meeting on LWR Fuel Performance September 19-22 Orlando, Florida.
The microscopic defects in the UO2 crystal structure can strongly influence fission gases transport out of grains and release from fuel pellets. These defects include point defects, such as vacancies, interstitials and fission atoms and extended defects, such as bubbles, pores and dislocations. A model for the dislocations generation and evolution in irradiated UO2 fuel has been developed and implemented in the mechanistic code MFPR along with a fuel densification model. Being combined with the set of equations describing evolution of point defects ( vacancies, and interstitials) and their interactions with fission gas bubbles, a completely self-consistent consideration of the whole system of point and extended defects in irradiated UO2 fuel has been obtained.
The resulting new MFPR version was successfully tested against irradiation experiments, in which the dislocation density and the bubble concentration and mean size were directly measured for various fuel burn-up and in annealing regime.
(1) Nuclear Safety Institute of the Russian Academy of Sciences (IBRAE) Moscow (Russia)
(2) Service d’Etudes et de Modélisation de l’Incendie, du Corium et du Confinement Laboratoire d’Etudes des Produits de Fission