Diverse Models for Graphite Brick Deformation and Stress State in UK AGR Nuclear ReactorsJ. Burrow , A. Bond ,
 Quintessa Ltd, United Kingdom
The UK Advanced Gas-cooled Reactor fleet, operated by EDF Energy, utilize a graphite core consisting of a lattice of around 3000 annular bricks. Due to irradiation, oxidation and thermal effects, the bricks deform and loose mass as they age. Of key concern is the late-life behavior of the bricks, in particular the predicted time at which brick shrinkage reverses into expansion, generating large stresses and potentially giving rise to cracking at the keyways. A calibrated 3D non-linear model has been built using the COMSOL Multiphysics® Geomechanics and Structural Mechanics modules, to explore the sensitivity of brick deformation and stresses to variability in different properties and different modeling assumptions.