Safety Analysis in VVER-1000 Due to Large-Break Loss-of-Coolant Accident and Station Blackout Transient Using RELAP5/SCDAPSIM/MOD3.5

Abstract

It is crucial to do safety evaluation of different postulated transient scenarios in actual nuclear power plants (NPPs). Some of the common analyzed scenarios are primary coolant tube rupture and station blackout (SBO). In this research, it was supposed that after establishment of a steady-state condition, an instantaneous guillotine large-break loss-of-coolant accident (LB-LOCA) of 850-mm inside diameter in one of the reactor vessel cold legs occurred, accompanied with SBO. The event progression and the variation of different reactor parameters like loop pressures, mass flow rates, fuel and clad temperature, injection rate of accumulators (ACCs), decay, and reactor power were investigated using the RELAP5/SCDAPSIM/MOD3.5 thermal-hydraulic program. The reactor consequences due to availability and unavailability of passive ACCs were compared. These kinds of analyses assist in estimating the time available to perform operator safety actions. This in turn aids in emergency planning and severe accident management. The results reveal that fuel damage decreased after the introduction of ACCs. Actuation of ACCs at their actuation setpoints provided core cooling by injecting water into the reactor core. However, ACCs alone are inadequate to contain long-term core cooling during a persistent LB-LOCA. The results obtained in the research were compared with MELCOR 2.1 and ASTEC V1.3, and a cohesive agreement was obtained. Therefore, RELAP5/SCDAPSIM/MOD3.5 is capable of modeling a LB-LOCA and SBO in VVER-1000, and it provides a significant analytical capability of safety systems for specialists in the field in NPP safety.

Keywords:

• Nuclear safety
• station blackout
• loss-of-coolant accident
• accumulators
• passive safety system

Acknowledgments

The authors would like to thank IAEA–African Regional Cooperative Agreement for Research, Development and Training related to Nuclear Science and Technology (AFRA) and the Nuclear and Radiation Department of Alexandria University for support rendered toward the study. The authors also thank Innovative Systems Software and Chris Allison for providing the VVER-1000 input and the regional training centre for letting us use RELAP5/SCDAPSIM/MOD3.5. Last, we would like to thank Mohosen Salehi and Caroline C. S. Bwanali for their sincere help and advice in making the nodalization of VVER-1000 and manuscript editing, respectively.

Disclosure Statement

No potential conflict of interest was reported by the authors.