Concentration phenomena for neutronic multigroup diffusion in random environments

Concentration-diffusion phenomena of heat convection in an incompressible fluid

We study in the whole space Rn the behaviour of solutions to the Boussinesq equations at large distances. Therefore, we investigate the solvability of these equations in weighted L∞-spaces and determine the asymptotic profile for sufficiently fast decaying initial data. For n = 2, 3 we are able to construct initial data such that the velocity exhibits an interesting concentration-diffusion phen...

Quenched large deviations for multiscale diffusion processes in random environments*

We consider multiple time scales systems of stochastic differential equations with small noise in random environments. We prove a quenched large deviations principle with explicit characterization of the action functional. The random medium is assumed to be stationary and ergodic. In the course of the proof we also prove related quenched ergodic theorems for controlled diffusion processes in ra...

Three-dimensional h-adaptivity for the multigroup neutron diffusion equations

Adaptive mesh refinement (AMR) has been shown to allow solving partial differential equations to significantly higher accuracy at reduced numerical cost. This paper presents a state-of-the-art AMR algorithm applied to the multigroup neutron diffusion equation for reactor applications. In order to follow the physics closely, energy group-dependent meshes are employed. We present a novel algorith...

Multigroup diffusion preconditioners for multiplying fixed-source transport problems

Several preconditioners based on multigroup diffusion are developed for application to multiplying fixed-source transport problems using the discrete ordinates method. By starting from standard, one-group, diffusion synthetic acceleration (DSA), a multigroup diffusion preconditioner is constructed that shares the same fine mesh as the transport problem. As a cheaper but effective alternative, a...

Parallel Solvers for the Transient Multigroup Neutron Diffusion Equations