Structural design and analysis of a mixer pump for beyond-design- basis load

This paper presents the results of the structural evaluation of a mixer pump for a postulated drop accident. The mixer pump will be installed in a double-shell tank at the Hanford Site, near Richland, Washington. This tank has a 1,000,000-gallon (3,785,000 liter) capacity and is used to store radioactive waste before final disposal. The beyond-design-basis load case presented here is a postmulated drop of the pump during installation or removal. It is assumed that the pump assembly might be dropped approximateely 140 ft (15 m) from a height at which the bottom of the pump assembly is slightly above the top of the access riser to the bottom of the tank. The acceptance criterion for this load case is that the pump assembly shall not penetrate the primary tank liner. To ensure the integrity of the liner, the kinetic energy (developed in the pump drop) must be absorbed by some means to limit the impact force on the tank dome and thereby keep the pump from contacting the bottom of the tank. The limited clearance near the mounting assembly warranted an innovative two-step design of the energy absorbing system to limit the impact force on the tank dome to anmore » acceptable value. This innovative design incorporates two energy absorbers in a unique series arrangement, one with the pump assembly and tile other in the pump pit.« less