This paper presents observations from analyses of pipe breaks presumed to occur in the Pebble Bed Modular Reactor’s (PBMR’s) Main Power System (MPS), and a brief insight into the implications of evaluated shear ratio values on dust lift-off and dust deposition in the MPS. The PBMR is a multibillion rand project tasked with the design, construction, commissioning and marketing of first-of-a-kind pebble-bed, high-temperature gas-cooled nuclear technology. The main loop of the envisaged nuclear power plant comprises a single Brayton thermodynamic cycle that integrates the pebble-packed reactor to a system of heat exchangers and to a single-shaft turbine-generator-compressor system. The reactor coolant is helium which, under 9 000 kPa, exits the reactor at approximately 900 °C. This drives the downstream turbine in a direct action set-up, supplying the grid with roughly 165 MWe of electricity. The PBMR’s MPS and support systems have progressed to advanced design phases. Thermal-hydraulics analysis has played an integral role in providing input data to design and systems engineering functions. Twenty-eight critical positions around the MPS have been identified for the capture of parameters used to calculate shear ratios, which are used to estimate dust lift-off fractions that could result from the pipe break scenarios, and to predict nuclear doses likely to affect the reactor’s adjacent compartments and the immediate environment.

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