The Plutonium Finishing Plant, also known as the Z Plant, was part of the Hanford Site plutonium production complex in Washington state. During World War II, Hanford produced plutonium nitrate (Pu(NO3)2), which was shipped to the Manhattan Project's Los Alamos Laboratory, where it was turned into metallic plutonium and made into pits for nuclear weapons. After the war ended, the Los Alamos Laboratory moved to divest itself of production activities in order to devote itself to research. The Plutonium Finishing Plant was built at Hanford to carry out the purification and reduction of the plutonium to metallic form, known as "buttons", and then perform the casting, grinding, and lathing of the plutonium to turn it into pits. The plant operated from 1949 to 1989. In 1953, it began shipping plutonium buttons to the new Rocky Flats Plant in Colorado, which fabricated pits. Plutonium production peaked in 1965, when 4,500 kilograms was produced. Between 1957 and 1961, nine types of pits were produced at Hanford. Pit production ended in 1965, when the Atomic Energy Commission announced that henceforth this work would be undertaken at the Rocky Flats Site. As demand for weapons-grade plutonium declined after 1964, the Plutonium Finishing Plant began producing mixed plutonium-oxide uranium-oxide (MOX) fuel for Hanford's Fast Flux Test Facility and reactor-grade plutonium. Plutonium was valuable, and reducing waste saved landfill dispatches and preserved the long-term radiological safety of the area by not burying the highly contaminated waste. The Plutonium Finishing Plant reclaimed solid waste in its RECUPLEX facility, combustible waste in the 232-Z Incinerator, and liquid waste in the 242-Z Waste Treatment Facility. A multi-purpose Plutonium Reclamation Facility opened in 1964. A serious accident at the 242-Z Waste Treatment Facility occurred in 1976, when the contents of a glovebox containing americium and plutonium exploded, seriously injuring an operator, Harold McCluskey. This accident prompted a series of reviews and evaluations that led to the 1978 Department of Energy decision to close most of the Plutonium Finishing Plant's facilities. Before the plant could be demolished, approximately 18 metric tons of plutonium-bearing material was stabilized between 1996 and 2004. Legacy plutonium from plant systems was removed by 2005, and all weapons-grade plutonium was shipped to the Savannah River Site by 2009. Demolition work on the plant began in 2017 and was completed in 2021.
Background During World War II, the Manhattan Project built the Hanford Engineer Works (HEW) to produce plutonium for use in atomic bombs. At the HEW, three nuclear reactors bred plutonium by irradiating uranium. The irradiated uranium slugs were sent to three radiochemical separation plants, where the plutonium was separated from uranium and fission product using the bismuth-phosphate process. The plutonium was then delivered to the 231-Z Plutonium Isolation Building in the form of 8-U.S.-gallon (30 L) batches of plutonium nitrate (Pu(NO3)2) in solution. This was further purified with hydrogen peroxide (H2O2) to separate the plutonium nitrate from its carrier and create what was called "AT solution". This was dried out, packaged in containers, and shipped to the Manhattan Project's Los Alamos Laboratory, where it was made into metallic plutonium and then formed into hemispheres for use in nuclear weapons. After the war ended, the Manhattan District began considering enhancements to the production processes. At the same time, there was a desire to relieve the Los Alamos Laboratory of engineering and production responsibilities. The new director of the Los Alamos Laboratory, Norris Bradbury, hoped to devote the site exclusively to research, but its CMR (Chemistry and Metallurgy Research) Division was fully occupied producing components and materials for nuclear weapons. The new operator of the HEW, General Electric, was asked to design a new facility that would handle the rest of the plutonium finishing process. This involved the conversion of plutonium nitrate to plutonium oxalate (Pu(C2O4)2, then plutonium dioxide (PuO2), and finally into metallic plutonium suitable for use in weapons and safer to transport long distances to the weapons assembly facilities. On 1 January 1947, the Hanford Site, along with the other nuclear weapons production facilities, passed to the control of the newly established Atomic Energy Commission (AEC). The AEC embarked on a program of expanding the facilities in response to the tensions of the Cold War. This included accelerating the design and construction of the proposed Plutonium Finishing Plant.
Design and construction In December 1946, a representative from General Electric visited the plutonium finishing and fabricating facility at the Defense Production (DP) West Building at the Los Alamos Laboratory to study its operation. Company representatives paid Los Alamos a second visit in the spring of 1947, and a design feasibility report was issued in July. The design of the Plutonium Finishing Plant was based on it, but incorporated several improvements. At Los Alamos, the operators manipulated the plutonium using rubber gloves inside a glovebox, but to cater for the greater volume of plutonium to be processed and consequent higher safety standards, the design called for Part I of the operation, the purification and reduction of the plutonium to metallic form, to be carried out by a mechanized process. Part II of the process would be casting, grinding, and lathing the plutonium into pits.
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