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JFNK preconditioning for coupled BWR calculations
Paper in proceedings, 2018

transfer and the interdependences between the various physics. The modelling assumptions were chosen so that the physics of BWRs could be properly accounted for with an as simple

as possible model. The model is thereafter used to study the effect of preconditioning when a Jacobian-Free Newton Krylov (JFNK) method is used to solve the system of equations.

Preconditioning is a key aspect in any JFNK method. By clustering the eigenvalues of the system of equations, a preconditioner is expected to drastically reduce the number of iterations.

Nevertheless, the design of an efficient preconditioner is a far from trivial task. Using the developed model, different preconditioning alternatives are tested. It is demonstrated that an

efficient preconditioner is found to have the following characteristics: separate preconditioning of the neutron transport problem, no preconditioning of the heat transfer

problem, preconditioning of the fluid dynamics problem where the cross-dependencies between the void fraction and the phasic velocities are resolved and where the pressure field

is treated independently. This paper thus provides guidelines about how to develop an efficient preconditioner for coupled BWR physics.

Boiling Water Reactor

preconditioning

coupled calculations

Jacobian-Free Newton Krylov

## Author

### Christophe Demaziere

Chalmers, Physics, Subatomic and Plasma Physics

### Sebastian Gonzalez-Pintor

Chalmers, Physics, Subatomic and Plasma Physics

### Anders Ålund

Fraunhofer-Chalmers Centre

Cancun, Mexico,

### Areas of Advance

Energy

### Subject Categories

Other Natural Sciences