Infrastructures are susceptible to aircraft impacts, as recent event by the 2001 terrorist attacks on the World Trade Center and the Pentagon. These attacks necessitated the need to urgently develop regulatorily requirements and guidelines for aircraft impact assessments, and specifically, for nuclear power plants. Currently, the basis of standards put in place (by the Nuclear Energy Institute, NEI) for assessing the shock effects of aircraft impact on nuclear facilities are not well understood while the methods and the basis for performing detailed structural analyses for assessing the structural damage are well defined. Moreover, the general information is not available to the public. Technically, the NEI’s guidelines are based on shock damages distances and median fragility limits, which is direction and frequency independent. Despite several studies on the shock damage due to aircraft impact, little has been reported about the frequency-dependent and median-based acceleration fragility.
To this note, a team of researchers organized under the leadership of KEPCO E&C: Mr. Randy James from Structural Solutions Consulting, LLC., Mr. Daniel Parker and Dr. Eric Kjolsing from Structural Integrity Associates, Inc., and Dr. Bong-Rae Kim and Mr. Daejoong Kim from KEPCO Engineering & Construction Company, Inc. developed a median-based fragility spectrum for different equipment categories with the objective of critically assessing the effects of shock due to aircraft impact on the equipment functionality, especially the nuclear facilities. Their work is currently published in ASCE Journal of Structural Engineering.
In their work, the shock fragility spectra were developed in three milestones. First, frequency-dependent median-based fragility spectra limits for different equipment categories were proposed based on the NEI’s guidelines. Second, acceleration time history demands were developed from the proposed shock fragility spectra. It is worth mentioning that the acceleration time history demands on shock propagation due to aircraft impact (obtained from studies) were used as seed functions in the spectral process and as demands in the time history analysis of the representative equipment. Eventually, the researchers also applied the spectrally matched time time-history demands on the representative equipment to analyze and validate the feasibility of the proposed shock fragility spectra in protecting nuclear facilities from aircraft impact effects.
Results showed that the representative equipment could remain functional for the proposed fragility spectra. The verification analysis was conducted in accordance with the structural assessment guidelines provided by the NEI, and the obtained results were consistent with the guidelines. Additionally, the authors observed that the defined capacities of equipment for surviving shock are appropriate for median-based analysis methods and could be assumed to be reasonable representatives of the actual equipment.
In summary, the study findings extend on the NEI’s guidelines fragility limits to frequency-dependent fragility spectra. For all the assessed equipment categories, the representative equipment remained operational for the proposed fragility spectra. In a statement to Advances in Engineering, Dr. Bong-Rae Kim, the corresponding author pointed out the proposed fragility spectra could be effectively used to develop region-specific safe distances as well as provide a detailed assessment of equipment survivability under aircraft impact.
James, R., Parker, D., Kjolsing, E., Kim, B.R., & Kim, D. (2020). Shock Fragility Spectra for Equipment Survivability under Aircraft Impact. ASCE Journal of Structural Engineering, 146(3), 04019211.