Earthquake simulator experiments for validation of numerical models for seismic fluid-structure interaction analysis of advanced reactors

Graduate Student: Faizan Ul Haq Mir

Principal Investigator: Andrew S. Whittaker

Project Completion Date: June 2022

Many safety-critical components in advanced nuclear reactors are filled with or submerged in fluids. To ensure that such components remain functional in the event of earthquake shaking, a detailed dynamic analysis that considers the effects of interaction between the components and the fluid is necessary. Although analytical solutions using different hydrodynamic theories are available, they cannot be applied to complex structural shapes and boundary conditions, multiple directions of seismic input, and moderate-to-severe earthquake shaking. Physical testing of advanced reactor components is not feasible given their size and cost. As advanced reactor designs move towards standardization of equipment to reduce associated costs, design and risk assessment calculations will have to rely on the use of verified and validated numerical models that are capable of capturing the interaction of the structural components with the surrounding fluid (fluid-structure interaction: FSI) over a wide range of three-component earthquake shaking. However, physical data that could be used for validation exercises is nonexistent. A three-phase experimental program using a 6 degree-of-freedom earthquake simulator at the University at Buffalo was executed to generate data for supporting validation of numerical models for FSI in commercial finite element codes. In the first two phases, a scaled model of a base-supported reactor vessel and simplified representations of reactor vessel internals (RVIs) were tested to generate hydrodynamic response histories for a range of seismic inputs. Added mass, added damping and coupling effects were investigated and strain and acceleration response histories were generated for the submerged components. The effects of seismic (base) isolation on hydrodynamic responses and dynamic responses of RVIs were investigated using friction pendulum bearings in tests or using numerically generated input motions simulating virtual isolation systems. The third phase of testing involved a scaled model of a prototype pebble bed reactor. The model involved representations of fuel pebbles, graphite reflector blocks, core barrel, vessel, and pebble handling and coolant circulating equipment atop the vessel head. Based on results of a scaling analysis, water was used to represent the coolant (Flibe) in the model. The reflector blocks were fabricated using polypropylene and the pebbles were represented by nearly 300 thousand polypropylene spheres. The effects of seismic isolation in reducing accelerations and deformations in different components were studied using Friction Pendulum isolators (single concave friction pendulum bearings and triple friction pendulum bearings) installed under the base of the vessel.

The data generated from the experimental program was used for validating an FSI solver in LS-DYNA. All data will be curated and archived to enable later use by analysts and engineers designing similar fluid-structure systems.

This project was supported by Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000978.