COMSOL Multiphysics ® is a general-purpose software platform, based on advanced numerical methods, for modelling and simulating physics-based problems. Since August 2015, Quintessa has been a COMSOL Certified Consultant.

The UK AGR fleet has been commercially generating low-carbon electricity since the 1980s, presently owned and operated by EDF Energy. The reactor design is somewhat unusual in that it uses a core of graphite bricks for the neutron moderator and carbon dioxide as the coolant. One aspect of the safety case that has come under particular scrutiny is the expected evolution of the graphite bricks and the expectation that they will crack late in the life of the reactor. Safe operation of the reactor has to be maintained at all times by ensuring that the reactor cores do not evolve to a state that is unacceptable under the current safety case. Knowledge of when bricks crack and how they subsequently evolve is therefore important.

The focus of the work in the COMSOL Multiphysics® software for EDF Energy has been to construct a diverse assessment of the reactor brick evolution, largely independent of their own internal modelling approaches, that could be used to predict the evolution of the shape of the bricks and the rate at which keyway root cracking will occur. The approach combines statistical models of the main model inputs, a nonlinear coupled mechanical model of the graphite, and the Monte Carlo approach to determine the cracking rates. The COMSOL Multiphysics® numerical model couples standard components of the add-on Structural Mechanics and Geomechanics modules for linear elasticity and thermal effects with customized partial differential equation (PDE) and ordinary differential equation (ODE) physics models to represent the highly specific "creep" and other, related processes that occur in graphite when in such an extreme environment. The results of the models have been compared against recent reactor data and have been found to give an excellent representation of keyway root crack progression and brick shapes, with only minimal tuning against the observations required.