The characteristics method in general geometry

Three very different transport theory methods - Monte Carlo, collision probability, and the characteristics method do have something in common: They all depend on some type of tracking procedure to calculate the interceptions of straight lines with surfaces that define different geometric or material regions. Thus, it is possible to develop a single ray-tracing module in general geometry that can be used for all three methods. Vujic developed such a module based on the Monte Carlo - type combinatorial geometry ray tracing and applied it to the collision/transfer probability (CTP) code GTRAN2. In this paper, we will describe the application and adaptation of the same ray-tracing methodology to the method of characteristics (MOC). Although both methods, CTP and MOC, are very accurate, MOC has the advantage over CTP for large many-region problems, because it requires less memory and CPU time