The Hanford Site is a mostly decommissioned nuclear production complex on the Columbia River in the U.S. state of Washington , operated by the United States federal government . Plutonium manufactured at the site was used in the first nuclear bomb , tested at the Trinity site , and in Fat Man , the bomb detonated over Nagasaki , Japan . During the Cold War , the project was expanded to include nine nuclear reactors and five large plutonium processing complexes , which produced plutonium for most of the 60,000 weapons in the U.S. nuclear arsenal . Many of the early safety procedures and waste disposal practices were inadequate , and government documents have since confirmed that Hanford 's operations released significant amounts of radioactive materials into the air and the Columbia River , which still threatens the health of residents and ecosystems . The weapons production reactors were decommissioned at the end of the Cold War , but the decades of manufacturing left behind of high-level radioactive waste , an additional of solid radioactive waste , of contaminated groundwater beneath the site and occasional discoveries of undocumented contaminations that slow the pace and raise the cost of cleanup . The Hanford site represents two-thirds of the nation 's high-level radioactive waste by volume . Today , Hanford is the most contaminated nuclear site in the United States and is the focus of the nation 's largest environmental cleanup
Trinity site
Trinity (nuclear test)
Nuclear safety in the United States