More Hall Annex

The More Hall Annex, formerly the Nuclear Reactor Building, was a building on the campus of the University of Washington (UW) in Seattle, Washington, United States, that once housed a functional nuclear research reactor. It was inaugurated in 1961 and shut down in 1988, operating at a peak of 100 kilowatts thermal (kWt), and was officially decommissioned in 2007.

The reactor was housed in a reinforced concrete building designed in the Brutalist architectural style by UW faculty members. They designed the reactor room with large windows that allowed observation from the outside, in an attempt to demonstrate the safety of nuclear energy.

The Nuclear Reactor Building was added to the National Register of Historic Places in 2009, after a campaign led by an architecture student in response to the proposed demolition of the building. A later demolition plan prompted a lawsuit from preservation groups, which ended with a court ruling exempting the building from the city's landmarks-preservation ordinance. The university demolished the building in July 2016 and will replace it with a new computer science building that is expected to open in January 2019.