Question: The Rocky Flats National Wildlife Refuge was previously a buffer zone for a production facility of what?
Context: The Rocky Mountain Arsenal National Wildlife Refuge is a 15988 acres National Wildlife Refuge located adjacent to Commerce City, Colorado, in the United States.  It is approximately 8 mi northeast of downtown Denver.  The facility is on the grounds of the former Rocky Mountain Arsenal, a United States Army chemical weapons manufacturing facility.  The site was designated a national wildlife refuge in 1992 by the United States Congress, and underwent a costly environmental cleanup in order to remove pollutants.  The refuge is managed by the United States Fish and Wildlife Service.  More than 330 species of wildlife inhabit the refuge, including raptors, deer, raccoons, coyotes, white pelicans, black-footed ferrets, black-tailed prairie dogs, and bison. Nantucket National Wildlife Refuge is a 24 acre range and was established in 1973 for its "particular value in carrying out the national migratory bird management program."  The refuge, which is cooperatively managed with The Trustees of Reservations, encompasses 24 acre at Great Point.  Nantucket National Wildlife Refuge is an un-staffed unit of the Eastern Massachusetts National Wildlife Refuge Complex.  Nantucket National Wildlife Refuge consists of the Northeast tip of Nantucket, known as Great Point.  The Refuge has been managed informally by TTOR several decades.  TTOR owns the land immediately adjacent to Great Point, known as the Coskata-Coatue Wildlife Refuge.  Great Point is known as one of the best surfcasting locations in New England because of the rip tide which brings bluefish and striped bass to the point.  The Refuge is also a destination for hundreds of visitors each year seeking to enjoy a Nantucket beach or a tour of the Great Point Lighthouse.  More information about the adjacent TTOR property is available on their website. The Yukon Flats National Wildlife Refuge is a protected wetland area in the U.S. state of Alaska.  It encompasses most of the Yukon Flats, a vast wetland area centered on the confluence of the Yukon River, Porcupine River, and Chandalar River.  The area is a major waterfowl breeding ground, and after a proposal to flood the Yukon Flats via a dam on the Yukon River was turned down, the Yukon Flats were deemed worthy of protection.  The Alaska National Interest Lands Conservation Act established the refuge in 1980.  It is the third-largest National Wildlife Refuge in the United States, although it is less than one-half the size of either of the two largest, the Arctic National Wildlife Refuge, or the Yukon Delta National Wildlife Refuge.  The refuge is administered from offices in Fairbanks. The Rocky Flats Plant was a former nuclear weapons production facility in the western United States, near Denver, Colorado.  Operated from 1952 to 1992, it was under the control of the U.S. Atomic Energy Commission (AEC), succeeded by the Department of Energy (DOE) in 1977. Audubon National Wildlife Refuge is a 14739 acre National Wildlife Refuge in the U.S. state of North Dakota.  The refuge is managed by the U.S. Fish and Wildlife Service and is the centerpiece of the Audubon National Wildlife Refuge Complex, which includes numerous other refuges in the region.  Originally designated as the Snake Creek National Wildlife Refuge in 1955, the refuge was renamed in 1967 in honor of the artist and naturalist John James Audubon.  Most of the refuge area is a lake known as Audubon Lake which is managed by the U.S. Army Corps of Engineers. The Desert National Wildlife Refuge is a protected wildlife refuge, administered by the U.S. Fish and Wildlife Service, located north of Las Vegas, Nevada, in northwestern Clark and southwestern Lincoln counties, with much of its land area lying within the southeastern section of the Nevada Test and Training Range.  The Desert NWR, created on May 20, 1936, is the largest wildlife refuge in the lower 48 states of the United States, encompassing 1.615 e6acre of the Mojave Desert in the southern part of Nevada.  This Range is part of the larger Desert National Wildlife Refuge Complex, which includes the Ash Meadows National Wildlife Refuge, the Moapa Valley National Wildlife Refuge, and the Pahranagat National Wildlife Refuge. Flattery Rocks National Wildlife Refuge is the northernmost of the three refuges (along with Quillayute Needles and Copalis) which make up the Washington Maritime National Wildlife Refuge Complex, a group of 870 islands, rocks, and reefs extending for more than 100 miles along Washington's coast from Cape Flattery to Copalis Beach.  These islands are protected from human disturbance, yet are close to abundant ocean food sources.  They are closed to the public, with wildlife observation only from boats and the mainland, and a 200-yard buffer zone surrounding each island. The Pahranagat National Wildlife Refuge is a protected wildlife refuge, located at the southern end of the Pahranagat Valley and administered by the U.S. Fish and Wildlife Service.  It is situated 90 mi north of Las Vegas, Nevada in Lincoln County, Nevada.  The 5380 acre refuge was created on August 16, 1963 and is part of the larger Desert National Wildlife Refuge Complex, which also includes the Ash Meadows National Wildlife Refuge, the Desert National Wildlife Refuge, and the Moapa Valley National Wildlife Refuge. The Rocky Flats National Wildlife Refuge is a unit of the National Wildlife Refuge System in the United States located approximately 16 mi northwest of Denver, Colorado.  The site was previously the Rocky Flats Plant's security buffer zone and is not currently open to the general public for access. Medicine Lake National Wildlife Refuge is a 31533 acre National Wildlife Refuge located in the northeastern region of the U.S. state of Montana.  The refuge is part of the Medicine Lake National Wildlife Refuge Complex which also includes the Northeast Montana Wetland Management District (WMD) and Lamesteer National Wildlife Refuge.  Medicine Lake is from the Assiniboine description of the lake, "Bda wauka" (medicine water).  The refuge was established in 1935 to protect habitat for various wildlife and especially migratory birds.  The refuge is managed by the U.S. Fish and Wildlife Service, an agency of the U.S. Department of the Interior.
Answer: nuclear weapons