Reactivity-Initiated Transients for 700 MWe PHWR

Safety analysis for Pressurized Heavy Water Reactor (PHWR) is carried out for various postulated initiating events as per regulatory requirement and may be categorized into normal operation, anticipated operational occurrences and design basis events etc. The analyses of these events are carried out with the objective of verifying that acceptable design limits are not exceeded for these categories. The safety analysis report is made based on the above-mentioned analyses. However, certain special transients are also analyzed to confirm the behavior of the reactor during such events to be within acceptable design limits. In present paper, we have analyzed certain reactivity-initiated plant transients like loss of regulation (LOR) incident for initial distorted flux shape, local change in reactivity due to pressure tube-calandria tube (PT-CT) break and inadvertent entry of fuel locator into coolant channel for 700 MWe PHWR, which allows boiling at the exit of coolant channel. The above transients have been carried out for the first time for Indian PHWRs with 3 dimensional transient code IQS3D based on improved quasi-static (IQS) approach coupled with thermal hydraulic computer code ATMIKA-T. The analysis results show that fast power rise during transients get terminated by reactor protection system and slow power transients are controlled by Reactor regulation system (RRS) and all safety parameters are within acceptable limits.