TRACE/S3K Code Coupling Simulation of a BWR/4 Anticipated Transient Without Scram

Abstract

The behavior of a BWR/4 subjected to an Anticipated “High-pressure” main steam isolation valve closure transient without scram (ATWS) has been predicted with the system code TRACE (V5.0) coupled to the core code SIMULATE-3K. The transient assumed highly reduced operator action and inoperative safety features (e.g., borated water injection). Thus, the reactor conditions became akin to station blackout, with only the Reactor core isolation cooling (RCIC) systems remaining potentially available. Scenarios based on this accessibility were simulated along with several sensitivity tests, i.e., decay heat, feed flow interruption delay, and code coupling mode. The results indicated that the cladding temperature reached the 1477 K limit in 15 min in case of total RCIC inoperability, while it remained well below this value in all other cases. For the latter, the time for the Pressure suppression pool water to reach the 350 K limit ranged between 1.1 hrs and 2.2 hrs.