Pickering Generating Station Primary Heat Transport Pressure Control Analysis During Boiler Steam Relief Valve Testing

Abstract

During recent boiler steam relief valve (SRV) test on units 1 and 4 in Pickering generating stations, several incidences of heat transport system liquid relief valve (LRV) opening were experienced due to an overshoot in primary heat transport (PHT) system pressure. This specific LRV has a lower setpoint compared to the other PHT LRVs. The test requires opening six boiler SRVs, one at a time. This LRV only opens on some SRV openings on some occurrences of the tests. Based on simulations performed using the Pickering Training Simulator and hand calculations, it can be qualitatively concluded that increasing the bleed capacity by means of readjusting the bleed valve travel stops and recalibrating the valve strokes can reduce the magnitude of pressure overshoot experienced during the tests and can consequently reduce the chance of the LRV opening during such tests. However, there are issues associated with increasing the bleed capacity. These issues include possible pipe vibrations due to the increased flow through the bleed valves and reduced IX column effectiveness due to possible operation of purification circuit relief valve. Alternatively, based on the fact that the opening of this LRV during large pressure transients is the original design intent, maintaining the current configuration, accepting occasional LRV opening during the tests in conjunction with careful investigation, and monitoring of valve life cycle for the LRV, preventative maintenance, and pipe integrity can also be considered. Investigating the above issues and analyzing each potential solution are the main focus of this paper. Quantitative analysis and plant transient simulations are used in deriving conclusions. Operations and maintenance priorities and concerns are then considered to formulate a recommendation and path forward. In this case, considering all of the above, the approach of reducing the SRV opening time was taken to dampen the effect of PHT pressure oscillation. This approach satisfactorily resolved the issue eliminating LRV opening in subsequent SRV tests.