Probabilistic assessment of aircraft hazard for nuclear power plants

Abstract As part of a general probabilistic safety analysis, the risk of structural damage to a nuclear power plant from aircraft crashes has been evaluated in a quantified manner. Frequency distributions of aircraft speed and weight and engine weight were constructed for small and large aircraft and for site locations adjacent to and remote from an airport. Based upon United States data an analysis of aircraft accidents is presented to establish the probability of an aircraft hitting a nuclear power plant. If an aircraft hits a building, either the whole building or just the local component may respond. It is shown that the response of the entire reactor building is negligible, and the damage to specific structural components is of concern. Components of a reactor building may experience structural damage in several modes as a result of an aircraft crash. It is essential that all modes of damage for any particular component are considered to establish the critical mode of damage. Further, depending upon various parameters involved, the critical mode of damage may vary for different components. For the specific case of an aircraft striking a reactor building, three modes of damage could be delineated. The aircraft engine might perforate the structural component. This type of damage is classified as perforation mode of damage . The second mode is classified as collapse mode of damage , where a local collapse of the structural system occurs. The third mode is classified as a cracking mode of damage , where the structural component ceases to function satisfactorily after the impact due to cracking. The 18-inch thick reinforced concrete sidewall of a typical boiling water reactor plant located at the top floor of the reactor building is used as an example. The probability of damage to this sidewall in the perforation and collapse modes is investigated. The results are compared to those obtained for the cracking mode of damage. Available empirical formulas for perforation of concrete are examined, and new formulas are proposed to cover the range of parameters encountered in aircraft engine impact. Uncertainties in formulation are discussed, and the probability of damage by this mode is determined using Monte-Carlo methods. The conditional probability of local collapse of the wall panel is evaluated by using probabilistic approaches and yield line theory. The striking location (and thus the critical yield pattern), moment, and rotational capacities are all treated as random variables. The probabilities of damage under the perforation and collapse modes are approximately of the same order of magnitude. Under the impact of an aircraft, the cracking mode of damage is estimated using elastic analyses. Solutions are obtained using a finite-element idealization and considering the maximum reactive force due to an aircraft strike as a static load. For the 18-inch wall under consideration, it is predicted that the cracking mode of damage occurs much earlier than the other two modes of damage. It is shown that the impact load level predicted for cracking mode of damage is very conservative. After a study of all modes of damage, it is concluded that the aircraft risk is usually acceptably low for the typical case studied here.