Abstract: Descriptions are on situations about the fuel ball flow in curvilineal channel of High Temperature Gas Pebble Bed Reactor, and on the method of solving that problem by using the programs with rectangular meshes. This method has been used for the physical design of HTR-10MW Test Module and can be spread over other problems with curvilineal meshes.

Key words: high temperature reactor, curvilineal mesh, rectangular mesh, flow channel