Title: A Jacobian-Free Newton Krylov Method for Reactor Fuel Pellet/Cladding Interaction Problems

Speaker: Glen Hansen, University of Idaho

Date/Time: Wednesday, January 5, 2011, 9:00 am      

Location: CSRI Building/Room 90 (Sandia NM)

Brief Abstract: This talk discusses the development of an initial thermomechanics model using a mortar finite element method to implicitly couple the behavior of the fuel pellet with the cladding. It begins with an overview of the typical behavior of light water reactor pellet fuel, and explains the physics that occurs between the pellet and cladding and in the helium-filled gap that separates the two. The relative motion of the pellets with respect to the cladding forms a challenging multiphysics problem where the heat generated in the fuel must travel through the gap (mostly via conduction) until the pellets contact the cladding later in the life of the fuel. A two way coupled thermomechanics problem results, where the heat equation solution is coupled to the equations of linear elasticity (weakly) through a thermal expansion term. Thermal expansion of the pellet and cladding, swelling of the pellet due to the accumulation of fission products, and creepdown of the cladding varies the gap distance.

The contact approach studied here is based on the mortar finite element method, where Lagrange multipliers are used to enforce weak continuity constraints across the gap. The resulting system of nonlinear algebraic equations is cast in residual form for solution of the transient problem. A preconditioned Jacobian-free Newton Krylov method is used to obtain the solution of the coupled constraint, mechanics, and heat equations. Several Trilinos packages are used in this development; Moertel supplies the mortar method, Nox is the nonlinear solver, Stratimikos is used as the interface to the block GMRES solver in Belos, and Ifpack and ML are used to form the preconditioner.

CSRI POC: Randy Summers, 505-844-6296