The Angra site contains the only two operational nuclear power plants in Brazil and one that is under construction. When Angra Unit 1 was designed the risk of tornadoes was deemed to be vanishingly small and tornadoes were not included in the design basis for the plant. When the question of environmental hazards was revisited for the design basis of Angra Unit 3, tornadoes were included as part of the design basis. Based on this change in philosophy for the Angra site, a review was performed and it was determined that the Raw Water Storage Tank and Reactor Make-up Water Tank, both of which are located outdoors at Angra Unit 1 required protection from tornado driven missiles. The tanks contain water that may be used for emergency cooling, and the water must be available for use during a design basis event. This paper provides an overview of the methodology used to design the tornado missile resistant shield structure for these two tanks.
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