By 1963, the Hanford Site was home to nine nuclear reactors along the Columbia River, five reprocessing plants on the central plateau, and more than 900 support buildings and radiological laboratories around the site. Extensive modifications and upgrades were made to the original three World War II reactors, and a total of 177 underground waste tanks were built. Hanford was at its peak production from 1956 to 1965. Over the entire 40 years of operations, the site produced about of plutonium, supplying the majority of the 60,000 weapons in the U.S. arsenal. Uranium-233 was also produced.