Acceleration techniques are essential for the efficient iterative solution of the transport
equation in reactor applications. We present two new acceleration techniques for the
method of characteristics in unstructured meshes. The DPN scheme generalizes a previous
asymptotic acceleration by incorporating a general DPN angular approximation for intercell
angular fluxes. In a radically different approach we show how to construct a scalar product
such that the transport operator becomes symmetric, and apply Lanczos' iterations. Both, the …