Abstract:

This paper presents the observations from the analyses of small, medium and large pipe breaks that are presumed to occur in the Pebble Bed Modular Reactor’s (PBMR) Main Power System. The PBMR is a multibillion-rand grossly ambitious project that is tasked with the design, commissioning and marketing of a first-of-a-kind pebble-bed, high-temperature and gas-cooled nuclear technology. The main loop of the envisaged PBMR nuclear power plant comprises of a single Brayton thermodynamic cycle which integrates the pebble-packed reactor to a system of heat exchangers, and to a single-shaft turbine-generator-compressor system. The coolant for the reactor is helium which under 9000kPa and exiting the reactor at close to 900 °C, drives the downstream turbine in a direct action setup, thereby supplying roughly 163MW of electricity into the grid. The PBMR’s Main Power System and its support systems have since progressed through to advanced design phases and thermal-hydraulics analysis has played an integral role in providing various design and systems engineering functions with the necessary input data. There are certain critical positions in the Main Power System (MPS) of the PBMR’s Demonstration Power Plant (DPP) that warrant analysis in order to determine the effect of pipe breaks on certain critical components. Twenty-eight positions around the MPS have been identified for the capture of the helium pressures, temperatures and velocities which are then incorporated into the shear ratio calculation. The calculated shear ratios are thereafter employed in estimating possible dust lift-off fractions that could result from the pipe break scenarios and also in the subsequent prediction of nuclear doses that are likely to affect the reactor’s adjacent compartments and the immediate civil environment. This work provides the observations captured from the pipe break analyses and a brief insight into the implications of the evaluated shear ratio values to dust lift off and dust deposition within the main power system.