Numerical study of hyperstoichiometric fuel creep (UO2+x) in fuel clad interaction of WWER1000

Nuclear fuel is faced with extreme thermomechanical environments during its operating time. In this period, fuel mechanical response is deeply influenced by inherent heterogeneous microstructures, dependent on stress and temperature. Under the reactions occurring inside the reactor, the fuel crystal will change, and the UO2 will be UO2+x. Creep as a slow deformation process, strongly affected by this irradiation. Indeed, the hyperstoichiometric crystals effect the creep rate and mechanical stresses. In this article, the thermomechanical behavior of WWER1000 fuel pellets considering the hyperstoichiometric fuel (UO2+x) is studied. Fuel swelling, densification, thermal stress and creep are numerically considered and pellet clad interactions (PCIs) are evaluated. For validating the model, the results for pellet clad interactions are compared with experimental data. The hyperstoichiometric study of fuel cladding mechanical interaction in WWER1000 shows advancement of mechanical interaction during fuel burnups. It is found while the fuel and clad interaction occurs in 50.8 MWd/kgU for UO2, by increasing the amount of x and hyperstoichiometric fuel in the pellet, the pellet clad interactions will occur in lower burnups. These advancements for several hyperstoichiometric fuels are calculated and results are discussed. (C) 2019 Elsevier Ltd. All rights reserved.