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TRACE/RELAP5 Calculation of NPP Krško SGTR Accident Under Realistic and SRP Conditions (NUREG/IA-0556)

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Publication Information

Manuscript Completed: November 2024
Date Published: June 2025

Prepared by:
Vesna Benčik, Davor Grgić, Siniša Šadek, Paulina Družijanić

A. Hsieh, NRC Project Manager

Division of Systems Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Prepared as part of
The Agreement on Research Participation and Technical Exchange
Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Published by:
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice

Abstract

Steam Generator Tube Rupture (SGTR) event leads to contamination of the secondary side due to leakage of the radioactive coolant from the Reactor Coolant System (RCS) through the broken Steam Generator (SG) tube(s). Unlike other loss of coolant accidents, an early operator action is necessary to prevent radiological release to environment. The SGTR for NPP Krško (NEK) was analyzed using TRACE 5.0p5 and RELAP5/MOD3.3 codes. Two groups of analyses, aimed to determine the Margin To ruptured SG Overfill (MTO) as well as Thermal Hydraulic conditions for radiological Dose (THD) calculation, have been performed. For each group two analyses were done; the analysis based on initial conditions resulting in most adverse outcome (so called SRP assumptions) and the analysis based on best-estimate initial conditions. Transient scenario and operator actions were taken from NPP Krško Emergency Operating Procedure (EOP) E-3, Steam Generator Tube Rupture, ref./7/. For THD analysis, cooldown and depressurization to Hot Shut Down (HSD) conditions (2.8 MPa, 450.15 K) has been performed. At that point Residual Heat Removal (RHR) system can be put in operation.

Page Last Reviewed/Updated Tuesday, June 17, 2025