Implementation of Automatic Trip of Recirculation Pumps During ATWS Scenario to Strengthen the TAPS-1&2 Reactor Safety

Tarapur Atomic Power Station (TAPS) is a twin unit boiling water reactor (BWR). It is a generation-1 BWR (BWR-1) and pre-mark-1, designed by General Electric (GE) of USA. It is operating since 1969. This paper discusses the Anticipatory Transients Without Scram (ATWS) in the context of boiling water reactors (BWRs) like TAPS-1&2. ATWS refers to a situation where the reactor scram fails to initiate during a reactor event in a BWR. A Probabilistic Safety Assessment (PSA) analysis conducted for the TAPS-1&2 reactors indicates that ATWS is one of the contributors to Core Damage Frequency (CDF). This paper discusses about importance of automatic trip logic for recirculation pumps over manual trip of recirculation pumps that is involved in response to ATWS. The ATWS scenario initiated from primary steam valve closure is considered, as it is the most severe due to the several human actions that are required in a limited time frame to handle the event. One of the major human actions is to manually trip the recirculation pumps in the given timeline after identification of the failure of SCRAM on demand. The study presented in this paper covers thermal hydraulic analysis with manual and auto trip of recirculation pumps under ATWS scenario. The study also includes the impact on CDF with manual action and auto trip for recirculation pumps.