The Core Protection Calculator System (CPCS) was the first implementation of digital computers in a nuclear power plant safety protection system. The system was based on first principles to calculate the specified acceptable fuel design limit (SAFDL) online. This approach provides the theoretical optimum safety margin. The first-of-its-kind system was installed in the United States at Arkansas Nuclear One Unit 2 (ANO-2) in 1980. Extensive efforts were made by Combustion Engineering and U.S. Nuclear Regulatory Commission (NRC) staff to gain licensing approval of the CPCS. Based on accumulated operating experience, numerous improvements were made to enhance the performance of the CPCS. The CPCS software provided the flexibility to readily accommodate these design changes. Currently, CPCS is implemented in 21 nuclear power plants in operation or under construction in the U.S.A. and Asia. The next generation CPCS will focus on optimizing the plant protection by improving the SAFDL calculation. By taking advantage of the advances in digital computer technology, the comprehensive safety analysis code will be used online. A more detailed core power map using the incore detector signals will be used as the basis of the departure from nucleate boiling ratio (DNBR) and local power density (LPD) calculation. A quick power reduction will provide adequate margin for most of the design basis events. For these events, CPCS will initiate a reactor power cutback as opposed to a reactor trip, which will maintain the plant at a safe condition with a reduced power level.

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