ANEMONA - a neutron transport code for general geometry reactor assembliesbased on the method of characteristics and R-function solid modeler

The method of characteristics (MOC) solves the transport equation along str aight lines, called characteristics, of the system. Along these lines the d ifferential operator of the Boltzmann equation reduces to a total derivativ e. The MOC methodology does not impose any limitation on geometry and allow s for an accurate treatment of highly heterogeneous systems. However, the a ctual treatment of arbitrary domains in terms of their flexible description and efficient ray tracing does impose difficulties which limited broader a pplication of MOC in reactor analysis, Most of the existing MOC codes descr ibe the geometry by lines and arcs with extensive input data, have difficul ty in sub-meshing, require a pre-defined condition of closed rays at starti ng points limiting the boundary sl;ape, and need a large number of polar an gles which prolong the execution time. A new MOC code, ANEMONA, has been de veloped to remove all these geometrical limitations. This unified and easy- to-use method is based on an R-function solid modeler approach that can acc ount for all heterogeneities with full flexibility in domain description, r ay map generation, ray tracing and boundary types. The ANEMONA's methodolog y has many advantages: an easy description of arbitrary domains and meshing ; allowed mismatch of the reflected rays; calculation of the reflected angu lar flux as the boundary mesh average; use of only two adequately chosen po lar angles; and the reduction in computational time by energy-dependent azi muthal ray map. ANEMONA has been tested on a number of benchmark problems w ith excellent results. (C) 2000 Elsevier Science Ltd. All rights reserved.