  The method of characteristics (MOC) is widely used for neutron transport
calculation in recent decades. However, the key problem determining whether MOC
can be applied in highly heterogeneous geometry is how to combine an effective
geometry modeling method with it. Most of the existing MOC codes conventionally
describe the geometry model just by lines and arcs with extensive input data.
Thus they have difficulty in geometry modeling and ray tracing for complicated
geometries. In this study, a new method making use of a CAD-based automatic
modeling tool MCAM which is a CAD/Image-based Automatic Modeling Program for
Neutronics and Radiation Transport developed by FDS Team in China was
introduced for geometry modeling and ray tracing of particle transport to
remove those limitations. The diamond -difference scheme was applied to MOC to
reduce the spatial discretization errors of the flat flux approximation. Based
on MCAM and MOC, a new MOC code was developed and integrated into SuperMC
system, whic h is a Super Multi-function Computational system for neutronics
and radiation simulation. The numerical results demonstrated the feasibility
and effectiveness of the new method for neutron transport calculation in MOC.
