Dynamic simulation of Indian PHWRs

System process dynamics of a specific nuclear power plant plays an important role in designing and tuning of different control systems. The control systems are designed to make the plant tolerant to expected and unexpected transients to avoid outages. Corrective action continues till the process variables are brought back to the normal operating condition. A design objective has been to make the intervention of the shutdown systems unnecessary in all cases. To evaluate and test new features such as design modification, new operating procedures, optimization of process parameters and controllers as compared to the existing procedures, an integrated process dynamic simulation model is required. The process dynamic simulation is basically devised to analyse anticipated plant operational transients and also some of the safety related transients. In the background of an operator-training simulator, an integrated fast executable process dynamic model is used. But one needs a versatile and an accurate process model to analyse the unusual occurrences reported from the operating plant sites for mitigating the consequences. Keeping all the above mentioned points in mind, mathematical models for all the major components and sub-systems of the 220 MWe and the 500 MWe PHWR were developed based on the conservation equations of mass, momentum, energy and equation of state. All the associated control systems are also modeled. The PHT system includes the reactor store with nuclear fuel, primary circulating pump (PCP), primary heat transport (PHT) system pressure controller with feed/bleed system and pressuriser (Surge Tank). The secondary system includes mainly the steam generators (SGs) process, the SG level and pressure controllers, apart from the various steam cycle components. All these models are integrated together to form the plant transient analysis computer code. Extensive transient analysis studies have been carried out using these codes, to check the various design parameters and controller settings. The paper deals with the details of the various plant transient analysis. (author)