Theoretical investigations on thermal-hydraulics of fast reactor fuel rod bundles

Velocity and temperature predictions have been made in a bundle of bare rods with liquid metal cooling by means of the finite element method. A variational principle is applied to develop the finite element relationships. The resulting set of nonlinear algebraic equations for the nodal velocities are solved iteratively using the Newton-Raphson method. The mixing length model of turbulence is applied to predict local velocities and temperatures right up to the wall including anisotropic effects of eddy diffusivities. The numerical results deal with the heat transfer both from the fuel rod surface into subchannels and between subchannels itself, formed by bare rods and arranged in triangular array. A comparison between predictions and measurements in a 19-rod bundle is presented and the agreement is fair