Title: Evaluation of safety for VVER-1200-based nuclear power plants during main steam-line break accidents

Authors: Md Shamim Hassan; Iffat Sharif; Abid Hossain Khan; Dipayan Sikder

Addresses: Department of Nuclear Science and Engineering, Military Institute of Science and Technology (MIST), Dhaka, Bangladesh ' Institute of Nuclear Power Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh ' Institute of Nuclear Power Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh; School of Mechanical and Manufacturing Engineering, University of New South Wales (UNSW) Sydney, Kensington, New South Wales, Australia ' Institute of Nuclear Power Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh; Bangladesh Atomic Energy Regulatory Authority (BAERA), Dhaka, Bangladesh

Abstract: In this work, Main Steam-Line Break accidents (MSLBs) in a VVER-1200 nuclear power plant were investigated. Three different break sizes, 100, 200 and 400 cm², were considered for two separate cases, one where SCRAM was initiated and another for anticipated transient without SCRAM (ATWS). Simulations were performed for 12 hours to observe the performance of the plant safety systems. Results revealed that Fuel Temperature Coefficient (FTC) and negative moderator temperature coefficient played a crucial role in keeping reactor thermal power under control in the absence of SCRAM. Sharp spikes in reactor power were observed for ATWS cases between 400 seconds and 600 seconds. For both cases, fuel and cladding temperatures were below 1875°C and 625°C, respectively, making failure highly unlikely. The containment pressure was significantly below 5 bar for all the scenarios. DNBR was greater than unity for MSLBs with SCRAM but went below for 400 cm² MSLB with ATWS, indicating possible boiling crisis.

Keywords: anticipated transient without SCRAM; beyond design basis accident; nuclear power plant; safety.

DOI: 10.1504/IJNEST.2025.150745

International Journal of Nuclear Energy Science and Technology, 2025 Vol.18 No.2, pp.128 - 173

Received: 23 Mar 2025
Accepted: 28 Aug 2025
Published online: 22 Dec 2025 *

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