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Kang, H. G.; Jang, S. C.; Eom, H. S.; Ha, J. J.
Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)2005
Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)2005
AbstractAbstract
[en] Safety-critical systems adopt the multiple-redundancy design in order to reduce the risk from the single component failure. The digitalized safety-signal generation system is also designed based on the multiple-redundancy strategy which consists of more redundant components when we compare their number with those of conventional mechanical components. This higher redundancy would clearly reduce the risk from the single failure of components, but raise the importance of the Common Cause Failure (CCF) analysis. This research aims to develop the practical and realistic method for modeling the CCF in digital safety-critical systems. Higher level of redundancy causes the difficulty of CCF analysis because the fault tree model with conventional CCF modeling methods will be impractically large. We apply the simplified alpha-factor method to the digital system CCF analysis. For example, in the case of 16-redundant-train system, this method could reduce the number of CCF basic events from 65519 to 1. The digital system is usually operated based on more complex logics when we compare it with the analog system because multiple functions could be performed in single processor. Therefore the CCF probability calculation of the digital system should be carefully treated. This report presents the case study of the application of simplified alpha-factor method to the digital protection system of the Korean Standard Nuclear Power Plant (KSNPP). The number of components in a digital module for performing the safety functions is smaller than the total number of components in a module. In consideration of safety function actuation, we must consider the safety-critical components only. In order to consider this situation in a more realistic manner, we have to analyze the module design and hardware-software interactions. The different modules from different vendors could be used to perform the same safety function in order to reduce the CCF probability. The digital components, however, could be produced by the same vendor or the same process. This report also presents the method to cope with this situation
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Feb 2005; 75 p; Also available from KAERI; 9 refs, 18 figs, 14 tabs
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