Defence-in-Depth and Diversity (D3) as a fundamental principle for NPP safety assurance is analyzed. Reactor trip systems and engineered safety features actuation systems as a I&C part of NPP Defence-in-Depth infrastructure are multiversion systems (MVSs) according to international practice and standards requirements. The features of D3 analysis for multiversion FPGA-based NPP I&Cs are described. The requirements of existed standards are not enough detailed to make decisions concerning D3 and diversity taking into account FPGA features. Standardized and detailed techniques should be developed to assess actual diversity, choose types and volume of diversity according to criterion “required safety/ minimal cost”. The technique based on application of CMD (check-list & metrics & reliability block diagrams/Markov’s models) approach is suggested to assess MVS safety. Structures of multi-version I&C systems based on the Radiy FPGA platform are assessed by use of these techniques. Tool for D3 analysis of multi-version NPP I&C systems is described.

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