Sensitivity analysis of safety system architectures

Indian reactors traditionally adopted 2-out-of-3 (2oo3) architecture for safety systems. But, contemporary reactor safety systems are employing 2-out-of-4 (2oo4) architecture in spite of the increased size and cost due to the additional channel. This motivated us to carry out a comparative study of 2oo3 and 2oo4 architecture, especially for their dependability attributes - safety and availability. Quantitative estimation of safety and availability helps in adjudging the worthiness of adopting the architecture. The architectures are analyzed for their sensitivity against channel failure rates, repair rates, diagnostics coverage and periodic surveillance test interval. With all these parameters, system is modeled as Markov regenerative process and analyzed. An exhaustive analysis of dependability attributes with respect to the variation in system´s parameter has been presented.