The Monticello plant in Minnesota, USA was shut down after a beam supporting the turbine control valve enclosure in the plant's turbine hall broke loose from the building's overall structure, dropping onto a steam pipe. Pipe integrity was maintained and no steam escaped. Safety systems at the plant promptly shut it down as turbine control mechanisms in the enclosure malfunctioned, opening main steam isolation valves that subsequently activated sensors and triggered a full shutdown. All the plant's safety systems functioned normally and there was no release of radioactivity or threat to the health and safety of the workers and of the public.