Method of characteristic direction probabilities for heterogeneous latticecalculation

A new transport theory method of characteristic direction probabilities (CD P), which can treat complicated geometries with computational efficiency, i s presented. In the method, the entire problem is divided into subsystems o r cells that are further subdivided into finer mesh regions (i.e., computat ional meshes). Within a subsystem or cell, the fine meshes are coupled by t he directional transmission and collision probabilities for each characteri stic direction. In other words, all fine meshes in a subsystem are not coup led together but only the fine meshes along the characteristic line are cou pled for each direction. This is in contrast to the traditional collision p robability methods (CPMs). To calculate the directional probabilities, ray tracing with the macroband concept is performed only on each subsystem type . To couple the subsystems, the angular flux (not the current as in the int erface cut-rent method) on the interface between the adjacent subsystems is used. Therefore, the method combines the most desirable features of the di screte ordinates methods and those of the integral transport methods. To ve rify CDP, it is applied to two benchmark problems that consist of complex m eshes and is compared with other methods (CPM, method of characteristics, a nd Monte Carlo method). The results show that CDP gives accurate results wi th short computing time.