A new multi-domain DPN technique to accelerate the method of characteristics in unstructured meshes

The paper presents the last developments of the acceleration techniques for the Method Of Characteristics (MOC) in the code Apollo2. The main contribution concerns the introduction of a multi-domain DPN technique where all regions belonging to the same macro-domain are coupled by an integral operator that is strictly equivalent to the MOC. Different macro-domains are coupled via currents that are defined with the DPN formalism. In order to construct this new Integral DPN (IDPN) operator, transmission and escape probabilities must be computed that respect symmetries/anti-symmetries properties that are enforced to preserve the physics of the problem and to save computational effort. The paper presents results on realistic assembly calculations that show the good performance of the method. (author)