Integrated blast resistance model of Westinghouse AP1000 nuclear power plant auxiliary facilities

Introduction: Nuclear energy standards, guidebooks, manuals and related researches refer mainly to the protection of a nuclear power plant (NPP) containment structure, where the nuclear reactor is located, against different internal and external extreme events. However, neither NPP's auxiliary facilities nor man-made extreme event of air bomb or cruise missile explosions are considered. A novel integrated blast resistance model (IBRM) for a typical NPP reinforced concrete auxiliary facility subjected to an external above ground explosion is presented. The model evaluates two phenomena created by the blast that might cause failure to the NPP safe operation and might lead to radioactive leakage. The first is the facility's external structural damage, analyzed by single degree of freedom (SDOF) dynamic analysis combined with spalling and breaching empirical correlations. The permissible damage, determined by the authors according to relevant literature, should not exceed the elastic limit defined by the ductility ratio that is less or equal to one and by the supports' angle of rotation that is less or equal two degrees. The second is the in-structure motions caused by the air-induced ground shock and direct-induced ground shock due to the air blast loading, defined by empirical formulas, which are compared with the engineering systems allowable spectral accelerations.

Methods: The external wall of Westinghouse AP1000 NPP's control room, as well as its typical monitor & control engineering system, are analyzed against an external above ground explosion of Scud B-100 at various stand-off distances. The equivalent charge weight is one ton of Tri Nitro Toluene (TNT) assumed as hemispherical bare charge. The IBRM takes into account both structural damage evaluation and the in-structure motion due to the compression wave, which is caused by the external explosion.

Results: Based on the suggested damage levels of the IBRM, the control room is considered as safe if the missile explodes at stand-off distance greater than 60m. If the representative monitor & control engineering system is properly damped in the vertical direction, the control room could be considered as safe at stand-off distances greater than 35m. The structural damage occurs only at stand-off distances smaller than 20m.

Conclusions: This model can be used for other NPP's auxiliary facilities and their engineering systems based upon their specifications. Future work will include cased charges fragmentation effects of impact and penetration.