Acceleration techniques for the characteristic method in unstructured meshes

Acceleration techniques are essential for the efficient iterative solution of the transport equation in reactor applications. We present two new accel eration techniques for the method of characteristics in unstructured meshes . The DPN scheme generalizes a previous asymptotic acceleration by incorpor ating a general DPN angular approximation for intercell angular fluxes. In a radically different approach we show how to construct a scalar product su ch that the transport operator becomes symmetric, and apply Lanczos' iterat ions. Both, the DPN and Lanczos' accelerations, are able to accelerate high er angular flux moments. Numerical tests for realistic assembly geometries are used to compare the efficiency of the acceleration methods. (C) 2001 El sevier Science Ltd. All rights reserved.