Reliability Optimization of Safety Monitoring and Protective Systems

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This study introduces an optimal logic structure of a safety monitoring system to minimize the expected total loss incurred upon fail-dangerous failures or fail-safe failures.1. The safety monitoring system composed of several channels are considered. The problem is to design an optimal coherent structure for each channel when the channels are logically connected according to an accident occurence mechanism. For the one-channel system, the optimal channel structute is proven to be <k^*> -out-of-n: G, and <k^*> can be calculated analytically. For the multi-channel system, the optimal channel structure is a k-out-of-n: G, and the problem is formulated as a non-linear integer programming which can be solved by the extended Lawler and Bell's method. The above results are generalized to cover more general optimization of the logic structure without assuming ad-hoc channel connections.2. The optimal shut-down logic is developed for the overall protective system, which is composed of the driv … More ing, judging, and sensing sections. The optimal shut-down logic is determined by a switching function. For the system with reliable judging and driving sections, the optimal shut-down logic can be determined based on the reliability information of the sensing section.3. The optimal dynamic logic is developed for safety monitoring systems, where the term "dynamic" means that the logic is reconstructed every time when new nomitored data are obtained. The optimal dynamic logic is determined by a switching function of a history of monitored data, and it minimizes an expected damage caused by the two failures at the next monitoring time.4. The optimal decision logic for diagnosis of multi-sensor systems is developed to improve plant availability and safety. An expected loss caused by the two failure modes is minimized, and the resultant optimal diagnostic logic is determined by signatures of a switching function which, in turn, expresses efficiency of the diagnosis. An analytic representation of the optimal logic can be simplified considerably if importance rankings of measurement data are exploited. Less