Numerical evaluation of the severity of consequences of external fire and explosion incident at a nuclear power plant

Abstract

The International Atomic Energy Agency emphasizes on the safety assessment of fires involved by the crash of a large commercial aircraft into a nuclear power plant. In the guideline, it requires that a total load of aviation fuel that causes damage to exterior plants’ components should be included when performing the initial stages of the nuclear plant site evaluation process and over the entire lifetime of the plant operation. In this study, the effects of jet fuel and hydrogen-induced external explosion on a nuclear power plant was investigated and analyzed. A turbulence model based on Reynolds-averaged Navier-Stokes CFD solver, called FLACS, was used to determine the explosion parameters within the plant vicinity. The simulation results of key explosion parameters for butane explosion show a deflagrative overpressure of 0.27 bar and impulse load of 0.015 bar·s at some preselected position. An elevated local temperature of about 2030 K is recorded for this fuel. Hydrogen explosion causes a maximum overpressure of 0.37 bar, and a maximum positive pressure impulse load of 0.022 bar·s at the exterior walls of building structures. From the findings, it showed that building obstacles have a substantial influence on the evolution of fireball and overpressure propagation. The computed overpressure and impulsive loadings observed are capable of causing substantial structural damages and vulnerabilities. A significantly elevated flame temperature recorded would have a harmful effect on the safety function of structures, systems and components (SSCs) that are needed to execute reactor shutdown. The findings of this study may be used to revisit the safety evaluation of a nuclear power plant (NPP) site with regards to the risks and consequences associated with external explosion due to aircraft impact. It is also useful in designing the layout of the NPP and site placement of relevant items important to safety.