FDS simulation of the fuel fireball from a hypothetical commercial airliner crash on a generic nuclear power plant

Abstract

In the aftermath of 9/11 events it became clear that the impact of a fast flying commercial airliner hitting the NPP could no longer be excluded as a potential external hazard threatening the nuclear power plant (NPP) safety. One of the potential consequences of the impact is the occurrence of a fireball, large enough to engulf the entire NPP. The knowledge about fireballs from air crashes is rather poor since it is only based on footage shot by chance. From careful physical and chemical examinations using first principles, it can be concluded that the physics and chemistry of the kerosene fireball are similar to BLEVE fireballs in gas tank accidents which have been studied during the last decades. The knowledge from these analyses can be applied to air crash fireball analysis. In order to obtain an adequate understanding of the potential hazards to a NPP engulfed by a fireball a detailed analysis of the fireball is necessary. It is only by a detailed analysis that the effect of the NPP structures on the evolution of the fireball can be derived. Though the safety-relevant parts of the NPP are strong concrete structures, according to IAEA regulations the hypothesized entry of combustion products into ventilation or air supply systems and the entry of fuel into buildings through normal openings have to be analyzed in detail. This requires local transient values of the safety-relevant fireball parameters. With the NPP being a very large structure an adequately detailed simulation requires large computing grids and substantial computing power. With the release of Version 5 of the Fire Dynamic Simulator (FDS) from NIST in 2007 a simulation tool is now available which is capable to perform simulations of large fireballs on sufficiently large computing grids. These fireball simulations can be performed also by any other CFD code in which the relevant models have been implemented. The FDS fireball simulation capabilities were validated with the help of a well-documented fireball event, in which 5.9 to of propane were burnt during a BLEVE impact experiment conducted by the German BAM in 1999. To demonstrate the applicability of FDS to nuclear safety analysis a simulation of the impact of a 90 to fireball on a generic NPP was performed. The results are presented in this paper and show that FDS release Version 5 is an adequate tool to analysis the effect of a fireball on a NPP, even if the largest possible amount of kerosene involved in the crash is assumed. The work presented in this paper is based on codes, papers, footage and material that are freely available on the Internet. The paper does not use any information that is not freely available on the Internet.