[en] The digital control system is one of the advanced design features adopted for improving the technical and economical advantages for Korean Next Generation Reactor (KNGR). Due to the safety constraints of nuclear power plant, the advanced I and C and MMI systems have been required to be designed to protect the system against failures of I and C and MMI equipment which may degrade the performance of more than one major control or monitoring function. The functional and physical designs of these systems are segmented or explicitly incorporate other functional defensive measures to inhibit the propagation of failures across major functions. The functional and component grouping methodology, which is called 'segmentation', has been analyzed and the optimal segmentation methodology is suggested in this paper