Some energy consumers require power on a 24/7/365 basis with a high level of certainty, including defense installations, isolated communities and some industrial processes. For these customers, interruptions in electricity or heat can mean substantial financial loss or even the loss of lives. In the absence of grid-scale energy storage, a high level of power reliability can only be accomplished through the robustness and redundancy of power generators. The NuScale small modular reactor design is well suited to provide highly reliable power because of several features related to both the nuclear steam supply system and the overall plant design. In analogy to RAID (redundant array of independent disks) systems used to provide highly reliable data storage, a NuScale plant can assure sustained power generation by virtue of its redundant array of integral reactors (RAIR).This paper describes the NuScale RAIR plant features and summarizes the results of a rigorous analysis of RAIR reliability as a Junction of power, or conversely, the RAIR plant output power as a function of power reliability. The analysis utilized MATLAB and included probability distributions for the frequency and duration of module outages due to planned and unplanned events. The study also evaluated the impact of implementing turbine bypass rather than cold shutdown and using one or more modules to supply house loads in the case of loss of offsite power. Reliability results are presented for a 12-module RAIR plant with and without turbine bypass during a loss of offsite power enabled, and different possible connections to the offsite power distribution grid and dedicated service loads. Results indicate that a very high level of reliability can be achieved at relatively high power output levels, especially when turbine bypass is enabled in the 12-module plant, coupled with a direct connection to a dedicated service load.
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