Hourglass Reduction Measures in Hard Turbine Missile Impact into Concrete Protective Barrier

Failure of rotating machinery in nuclear power stations may result in ejection of fragments with high kinetic energy. Pieces of the disk or blades of a damaged turbine may cause failure of surrounding systems, structures, and components. The current paper presents study of effect of turbine disk fragment ejected as hard missile on the capacity of the protective walls of safety-related nuclear building. The investigation is performed by the missile-target interaction method, i.e. impact simulation of the model of the missile (i.e. the disk fragment) into the model of the protective barrier. Detailed model of the target is generated utilising non-linear material models for rebar steel and concrete. Different scenarios are investigated to define the most unfavourable impact with respect to the protective capacity of the safety barrier. The acceptance criteria are adopted form the relevant international regulatory documents. Special emphasis is given to the hourglass reduction. Various options are studied such as the hourglass control keywords, mesh refinement and different element formulation. The outcome in terms of CPU time and fulfilment of the structural acceptance criteria is compared and conclusions are drawn.