The last operating reactor in Hanford was the N-reactor, a Chernobyl type reactor. It was built in 1963 and has a graphite-moderated water cooled core with no concrete containment dome. The reactor has the highest peak power (4000 MW) of any reactor in the US and is designed to produce the maximum amount of plutonium per unit of uranium used. It supplied 20 percent of the nation's plutonium plus electricity for the NW.
On May 19, 1986, three nuclear safety experts testified before the House Interior and Insular Affairs subcommittee that a Chernobyl type accident was possible at the N-reactor and in the case of an emergency highly radioactive cooling water could just be dumped directly into the Columbia River.
Later that year, John Herrington, US Energy Secretary, commissioned an independent safety review by six nuclear experts. Four of the experts recommended remedial safety measures but supported continuing operation of the plant. However, two of the experts recommended the reactor be permanently shut down.
Throughout the Chernobyl crisis, the DOE had maintained that all their reactors were safe. Yet, with this latest report, the DOE announced the N-reactor would be shut down for a $50 million safety upgrade. $110 million was spent before the DOE announced the reactor would be placed in 'cold standby'. The reason given was that plutonium requirements for defense could be met at the Savannah River Plant in South Carolina.
After irradiation in the N-reactor, uranium was taken in heavily-shielded casks on a rail car to the Plutonium and Uranium Extraction (PUREX) plant on the Hanford site for chemical processing where it was dissolved in acid to separate out the daughter products of the fission process. On October 8, 1987, the PUREX plant was closed following disclosure of a catalogue of employee's safety violations.