This paper deals with the effect of fuel pellet eccentricity on fuel rod thermal performance in steady state and overpower transient condition. In this work, Governing Equations on the fuel pellet region and the clad region were set up in (r,θ) coordinates and solved by the use of Finite Element Method. To consider the variation in gap size with azimuthal angle, the angular-dependent gap heat transfer coefficient is used while concentric geometry is remained. Material properties are considered as a function of temperature and volumetric heat generation rate as a function of radial position. The main assumptions are that the coolant temperature and convective heat transfer coefficient are uniform with azimuthal angle.
The results showed the increase of maximum local heat flux at the cladding outer surface and the decrease of maximum fuel temperature due to pellet eccentricity. The increase of local heat flux at cladding outer surface is expected to affect the local DNBR and in turn the uncertainties in minimum DNBR calculation. Pellet eccentricity was found to introduce large asymmetry in fuel pellet temperature and movement of maximum fuel pellet temperature location. This trend was the same for both steady state and overpower transient condition.
