Reliability and redundancy allocation analysis applied to a nuclear protection system

Brazil is building, with national technology, two small nuclear reactors for propulsion and for the production of radioisotopes with thermal powers between 20 and 50 MW. These nuclear reactors fit more into the small modular reactor (SMR) class than the large nuclear power plant class. In this article, we apply the SMR design approach to propose a reactor protection system architecture for the small reactor under construction in the country. For this, the probabilistic analysis of the architecture of a protection system of a nuclear reactor is evaluated to determine the sensitivity of the components through a modeling of Reliability Block Diagram. The modification of the architecture and the addition of redundancies were evaluated when using components with a lower useful life than the components normally used for this purpose. The results showed that after one year of operation, the reference RPS system has a failure probability of 0.17%. The modified system, with components with a shorter life span, presents a point reliability value only 0.070% lower than the reference, but this difference grows exponentially with time, and in 10 years of operation it can reach values above 95%. The use of equipment with shorter life characteristics implies a greater number of redundancies and, in addition, a greater number of maintenance procedures and spare parts. Therefore, this technical feasibility analysis should consider RAM simulation as well. (author)