Nonlinear 3-D dynamic time history analysis in the reracking modifications for a nuclear power plant

An independent seismic response evaluation of spent fuel storage racks was performed on the reracking modifications for a typical operating pressurized water reactor type nuclear power plant using nonlinear dynamic time history analysis methods per the U. S. Nuclear Regulatory Commission (USNRC) criteria. The submerged free standing rack system and surrounding water are coupled due to fluid-structure-interaction effects using potential theory. Three dimensional (3-D) single rack and whole pool multiple rack finite element models were developed with features that allow the consideration of geometrically and materially nonlinearities including 1) the impact of a fuel bundle to a rack cell, a rack to adjacent racks or pool walls, and rack support legs to a pool floor; 2) the hydrodynamic coupling of a fuel assembly with a rack and of a rack with adhacent racks or pool walls; and 3) the tilting and frictional sliding of the rack supports. The methodologies and typical results using a 3-D single rack model as well as a 3-D whole pool multiple rack model developed herein are presented.