Nonlinear structural dynamics for assessing aircraft impact at nuclear power plants

The next generation of nuclear power plants is being designed worldwide with consideration for the effects of impact from a large commercial aircraft as a malevolent act. Detailed, realistic nonlinear structural analyses are required to assess the physical damage caused by an impact in order to meet regulatory requirements. In the U. S., industry developed methodology for conducting aircraft impact analyses have been accepted by the U. S. Nuclear Regulatory Commission (NRC) and requires advanced constitutive modeling of reinforced concrete, detailed and realistic structural modeling, appropriate material failure criteria, and realistic application of the impact load using robust explicit dynamics analysis software. The most common approach for load application is the Riera method that uses a force time history applied over a representative contact area as a pressure load. Sample studies demonstrate that the Riera method offers good analytical results for structural configurations that can fully resist the impact. For structural configurations that are insufficient to withstand the impact forces, the Riera method is useful for assessing the failure mode of the impacted wall, but the method fails to quantify the consequences of aircraft debris that penetrates beyond the initial point of impact. The sample studies also demonstrate that for some cases the design-basis structure can adequately meet aircraft impact requirements. For other cases where reinforcement is minimal or the span of the impacted wall is large, design enhancements can be made to offer the necessary resistance to limit damage to the exterior wall. If the impacted wall fails, the consequences of debris entering the plant can be determined by an alternative approach for load application called the missile-target interaction method. Further sample studies demonstrate that with this approach, the aircraft can be explicitly modeled and used to investigate a realistic extent of damage, which may be acceptable.