Synopsis The topic of aircraft impact is not new in nuclear power plant design. In 1968, the US National Regulatory Commission required the safety evaluation of the Three-Mile Island nuclear power plant against accidental aircraft impact. By the early 1970s, the aircraft impact problem was a subject of widening interest on both sides of the Atlantic. Two main trends were formed: the US concept, i.e. impact of commercial aircraft at landing speed and the German concept of impact of military fighter aircraft at flight speed. In 1974 an official design load was introduced by the German Department of the Interior; consequently, several national regulatory agencies introduced the load case of aircraft impact. After 1974, several plants in Switzerland, Belgium and all nuclear power plants in Germany have been specifically designed to resist accidental aircraft loading. Following these early studies, engineering attention was given to ‘the structural capacity’ and ‘induced vibrations’. The first aspect resulted in the evolvement of the double shell concept and specific provisions for crash resistant design of the external structures. The second aspect was treated similarly to seismic induced vibrations, i.e. using floor response spectra (FRS), thereafter used for equipment and components design. After the events of 11 September 2001, a new load came to the forefront; i.e. intentional impact of ‘large’ passenger airliners for which the loading parameters (i.e. peak force, load function shape, impulse) vary significantly from those used in former designs. The load induced by large aircrafts at high speed is capable of activating the global response of a typical reactor building. Hence, the loading is somehow between the classical ‘aircraft induced’ and the ‘seismic induced’ in terms of duration and frequency content, but with much higher peak values. To satisfy the new high demands, raised from this load case, new activities and investigations on the topic were initiated. Current research is focused mostly in three fields: 1) coupled analysis taking into account the missile-target interaction, 2) refined modelling and dynamic analysis of the target structure considering the material non-linearity, and 3) alternative procedures for the assessment of the damage potential of the induced vibrations additionally applied to the classical approach of using Acceleration FRS. The presentation will give an overview of the current concepts in the field of Aircraft Crash Impact Assessment of nuclear related facilities. It will cover the specifics in aircraft modelling and loading definition, target structure modelling and analysis, as well as approaches for structural capacity and equipment assessment. For equipment assessment, the use of alternative strong motion parameters which can be used as Damage Indicators, as well alternative assessment methods, will be presented and discussed. The talk will give an overview of a recently completed commercial project for the assessment of the engineering safety of contemporary NPP design for large aircraft crash impact. Some new research activities in the field of safety assessment of existing NPPs and the development of concepts for mitigation will be also highlighted.
Anton Andonov is a Chief Expert at Risk Engineering Ltd, Bulgaria. He has worked on several high-profile consulting projects in the field of structural analysis, design and assessment of various hazardous structures from the Nuclear, Hydro Power and Oil & Gas sectors for extreme external and internal loads. He is a member of EAEE, EEFIT and IABSE. He has several publications in the field of safety assessment of nuclear related facilities and large dams for extreme loads, and also lectures at the European Polytechnical University in Bulgaria.