The Instrumentation Grid Assembly (IGA) is a complex structure located in the upper head region of a nuclear reactor vessel (RV). It is used to support various in-core instruments running from the RV closure head (RVCH) penetrations to the reactor core. Qualification of the IGA per ASME Boiler and Pressure Vessel Code Section III is required by Westinghouse’s Design Specification. A structural analysis was carried out to demonstrate that the Code stress limits for various load levels were satisfied. These loads include deadweight, spring preload, pump pulsation load, random flow turbulence load, flow-induced vortex shedding load, seismic load, and loss-of-coolant-accident load. This paper describes the structural analysis methodology used in qualifying the IGA design for the Westinghouse AP1000 nuclear reactor.Copyright © 2010 by ASME