Quintessa

COMSOL Conference 2019

On 24th - 26th September 2019, Mark Pogson was one of the speakers at the COMSOL Conference 2019 in Cambridge. Mark gave a talk and presented a poster on the work Quintessa are undertaking in support of safety cases for the operation of the UK advanced gas-cooled reactor (AGR) fleet.  Mark was also an invited panellist for a discussion of Digital Twins and Industry 4.0.

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

The UK AGR fleet has been commercially generating low-carbon electricity since the 1970s and is presently owned and operated by EDF Energy. The reactor design uses a core of graphite bricks for the neutron moderator and carbon dioxide as the coolant. One aspect of the safety cases concerns the evolution of the graphite bricks and the expectation that they will crack as the reactors age. Safe operation 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 cases. Knowledge of when bricks might crack and how they might subsequently evolve is therefore important.

The aim of Quintessa’s COMSOL modelling work for EDF Energy has been to provide a diverse capability for modelling reactor brick evolution, largely independent of EDF Energy’s central modelling approaches. The capability focuses on predicting the evolution of the shape of the bricks and the rate at which cracking associated with keyways in the bricks will occur, termed keyway root cracking. The approach combines statistical models of the main inputs, a nonlinear coupled mechanical model of the graphite, and a Monte Carlo approach to determine the cracking rates. The modelling couples standard components of the Structural Mechanics and Geomechanics COMSOL modules for linear elasticity and thermal effects with customised 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 brick shapes and keyway root crack progression, requiring only minimal tuning against the observations.

Animation of model for evolution in graphite brick shape over 40 years, and with level of stress over the surface indicated. The stress scale varies from -30 MPa to 20 MPa. Developed with COMSOL Multiphysics.
Animated gif of graphite brick distortion in an Advanced Gas Cooled Reactor. (Full Resolution)