Evaluation of Accident Management (AM) actions in a Westinghouse 2-loop PWR during MSGTR using best estimate approach with TRACE v5p8 code

Steam Generators (SGs) in Pressurized Water Reactors (PWRs) serve as heat exchangers, transferring thermal energy from the radioactive primary coolant loop to the non-radioactive secondary loop. The structural integrity of SG U-tubes is important to prevent radioactive material from contaminating the secondary loop. A Steam Generator Tube Rupture (SGTR) is classified as a Design Basis Accident (DBA) and represents a significant safety concern. In more severe cases, multiple SG U-tubes may rupture simultaneously, resulting in a Multiple Steam Generator Tube Rupture (MSGTR), which is categorized as a Design Extension Condition (DEC) by the Swiss Federal Nuclear Safety Inspectorate (ENSI). MSGTR events present greater challenges than SGTR due to the rapid release of radioactive material, accelerated thermal-hydraulic changes, and increased complexity in Accident Management (AM) actions. This study focuses on evaluating AM actions during MSGTR scenarios for the 2-loop Westinghouse PWR. Key analyses include a double-ended guillotine rupture of two SG U-tubes under full-power conditions, with all reactor systems operational. The simulations conducted using the TRACE v5.0 code, examine critical parameters such as coolant mass discharged into the affected SG, releases through the intact SG valves, and maximum liquid level in the affected SG. Sensitivity studies investigate variations in steam blow-off from the intact SG and operator AM actions, extending beyond the initial 30 min of the transient until equilibrium conditions are achieved. The results aim to enhance understanding of MSGTR dynamics and optimize AM strategies to ensure reactor integrity, minimize environmental impact, and achieve safe shutdown conditions.