Simulation of a station black out at the Angra 2 NPP with Melcor Code

Abstract

The interest in evaluating the level of resistance of a nuclear power plant in response to an accident that exceeds the project bases, increased significantly after the Fukushima-Daiichi accident. Melcor is an integrated code, developed by Sandia National Laboratories, used to model and simulate the evolution of severe accidents in nuclear power plants. The Melcor modeling is general and flexible, making use of a “control volume” approach in describing the thermal hydraulic response of the plant. Reactor-specific geometry is imposed only in modeling the reactor core. The reactor cooling circuit and the four SG are represent by two model-loops, a single loop with the pressurizer and an agglutinated triple loop. All active safety systems which depend on AC power are assumed to be unavailable in this analysis. The most important strategies assumed were primary side depressurization and additional makeup water to reactor coolant system. The passive severe accident management measures primary bleed, secondary side bleed, passive injection from feedwater system and firefighting pool available. In Brazil there is the Almirante Álvaro Alberto Nuclear Power Plant that has two plants in operation, and one of them is Angra 2, which started operating in 2001. This unit is a pressurized water reactor type with electrical output of about 1350 MW. The objective of this work is to present a summary of the severe accident caused by a station black out condition using the Melcor 1.8.6 code. The main result of the study is an evaluation of RPV lower head integrity during a severe accidents scenario. The results will be useful to an independent assessment into the detailed processes involved by the management guidelines for one scenario severe accident in Angra 2.