Transient analysis following tripping of a primary circulating pump for 500-MWe PHWR power plant

The 500-MWe Indian pressurized heavy water (PHWR) incorporates many new features as compared to the earlier 220-MWe PHWRs. To evaluate the new design features like primary heat transport (PHT) system configuration with two loops, four primary circulating pumps (PCPs) and four passes through core, addition of a pressurizer (surge tank) in the PHT system along with a feed/bleed system and their safety-related implications, simulation model development and transient analyses are necessary. To mitigate the swell and shrinkage in the PHT system and to avoid high/low PHT system pressure during transients, a 30 m³ pressurizer along with feed/bleed system is also included in the PHT pressure control system for the 500-MWe PHWR. At the same time, a reactor stepback is also actuated during the one PCP trip transient after tripping the corresponding (same side) PCP in the other loop. The corresponding PCP in the healthy loop is tripped to avoid unsymmetrical flow and pressure distribution in the two identical loops. A detailed transient analysis is required to study the individual contributions of various systems and provisions such as pressuriser, feed/bleed, and reactor step/set back in mitigating the consequences of the malfunction.