7. UNUSUAL FEATURES OF THE PROGRAM
In this program, the leakage iterative method is applied which has the following characteristics: a. A fine-mesh difference approximation technique is applied only to the channels and layers. Therefore, it is not necessary to calculate the neutron fluxes at all fine-mesh points in the core and thus the computer time is reduced.
If the block which is formed by a channel and a layer, is a 12 cm cube and the mesh width is 2 cm, the number of fine-mesh points is 6x6x6=216.
In the present method, however, the number of mesh points is 6+(6x6)=42, that is about one-fifth of the former. The terms connecting the channel and layer calculations are only the neutron leakage and the neutron source, which reduce the computer memory required.
b. Since the neutron leakage from a block is calculated by a fine- mesh difference approximation, the discretization error is minimized.
c. When only one fine-mesh point is located in each block, this method becomes the same as a fine-mesh difference approximation. In this case, the iterative scheme corresponds to one of the variants of the Peaceman-Rachford iterative method. Therefore, it is possible to establish the condition under which the consistency is achieved between the axial and radial leakages in the same manner as ADI (alternative direction implicit iterative method due to Peaceman and Rachford), and it is easy to compare the results with those obtained from conventional fine-mesh difference approximation methods. The computer code can be used for calculating both the collapsed flux and the fine-mesh flux.