Sub-space iteration scheme for the evaluation of -modes of finite-differenced multi-group neutron diffusion equations

The recently known technique of sub-space iteration for non symmetric matrices is used to evaluate the dominant A-modes of finite-differenced multi-group neutron diffusion equations over a nuclear reactor. The multi-group problem is first cast in the form of a "reduced problem" in terms of the net fission sources in each mesh. This makes the implementation of sub-space iteration scheme easy since the external source option available in well-established static finite difference codes can be utilised to solve the problem. The scheme is applied to a test case which represents a typical CANDlJ reactor. The exploitation of reactor core symmetry to simplify the problem is also discussed.