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 (), 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 batches of plutonium nitrate () in solution. This was further purified with hydrogen peroxide () 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 (, then plutonium dioxide (), 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.
In August 1947, General Electric recommended that the Plutonium Finishing Plant be located within the fence of the 231-Z Plutonium Isolation Building, where it could use the existing boiler, water filtration, electricity, telephone, warehouse, road, and guard facilities. These all had to be expanded and extended to accommodate the new facility, but this was cheaper than building new ones. Plans initially called for Part I to be carried out in one building (234) and Part II in another (235), but in November General Electric decided to place them both in one building (which became 234-5Z) so the plutonium would be confined in gloveboxes throughout the finishing process.
Another deviation from the original design was the substitution of a manual process for a mechanized one. The facility was originally scheduled to open in late 1949, but in February 1948 the AEC communicated that it wanted the facility operational by 1 January 1949. In order to meet this deadline, General Electric decided to implement an interim rubber glove (RG) line akin to that used at Los Alamos, while continuing work on a remote, mechanized (RM) line.
Construction commenced in June 1948, when the concrete foundations and footings were poured. Work was also carried out on a new railroad spur and an extension to the 284-W Boiler House. Works involved of telephone lines, about of steam lines, of underground water pipes, and of air ducts. There was also a septic tank and of gravel roadway. For security reasons, instrumentation earmarked for the Plutonium Finishing Plant was stored in the warehouse in White Bluffs. Tests were conducted in gloveboxes in the 231-Z Building to establish procedures to be used in the new facility, using Karo syrup instead of AT solution.
By the scheduled start-up date of 1 January 1949, work on the 234-5Z Building was only 55 percent complete. Ten of the thirty process gloveboxes had been installed, and the first group of operations personnel were being trained. The start-up date was pushed back to 1 March. A 16-day strike by electrical workers in March and April further delayed completion. The building was handed over between 29 April and 6 May, and a full complement of 27 operators were trained by the middle of the month. Test runs were conducted to verify the equipment and procedures.
As built, the 234-5Z Building was long and wide. It had a steel frame surrounded by aluminum sheeting with rock wool insulation and 16-gauge steels. The floors of the two stories were concrete slabs. Some of the interior walls were reinforced concrete. The first floor contained the processing line, an analytical laboratory, and storage vaults for the plutonium. The second floor contained changing rooms, locker rooms, a lunch room, a conference room, and offices. Hanford personnel called it the Z Plant, because it was the last step in the production process.
Operations The Plutonium Finishing Plant commenced production operations on 5 July 1949. The RG line consisted of 28 gloveboxes operated by three shifts of operators who worked Monday to Friday. Training was not yet complete and the equipment was not fully functional. Negative air pressure was supposed to prevent airborne contamination, but samples taken in the processing area and the analytical laboratory were high enough to compel the operators to wear gas masks. Plutonium production fell short of the targets set by the AEC. On 24 October, the AEC called for increased production on the RG line, and authorized construction of a second RM line, although the first was still not operational. The two would become known as the RMA and RMB lines.
Although the RMA line was intended to commence operations in 1951, the start up was delayed by an AEC requirement to produce a different model pit, and operations did not commence until 18 March 1952. The RMA line included 30 stainless steel gloveboxes, 30 control desks, 10 control cubicles, 24 instrument panels, 9 resistance furnaces, 5 induction furnaces, and a conveyor belt. The RMA line was soon out-producing the RG line, and, in 1953, RG line modernization was abandoned in favor of improvements to the RMA line.
The RMB line began shakedown tests on 17 May 1952, but due to improvement in the RMA line, the RMB line became obsolete before it was completed, and it never processed any plutonium. A third RM line (RMC) was authorized in 1957, and workers removed the RMB line when they installed the RMC line, which became operational in October 1960. In the early months of 1953, the RG line handled only 5 to 6 percent of the plutonium nitrate sent to the Plutonium Finishing Plant, and produced no pits. In 1955, the RG line equipment was removed and buried. The space where the RG and RMB lines had stood was used by the RMC line, which cost almost $1.9 million (). The RMC line was soon producing 80 percent of the plutonium buttons. It ran seven days a week, operated by shifts of four to six operators and a line manager.
The AEC raised production quotas in September 1953, and the Hanford Site began shipping plutonium buttons to the new Rocky Flats Plant in Colorado, which fabricated pits from plutonium buttons. The following year the Savannah River Site became operational. The finishing plant at the Savannah River Site did not manufacture pits, but just buttons, which it shipped to Rocky Flats. In 1949, the Plutonium Finishing Plant produced about 750 kilograms of plutonium; in 1959, some 3,500 kilograms were produced. Between 1957 and 1961, nine types of pits were produced. In 1960, with the RMC line operational, more than 4,000 kilograms was produced. Production peaked in 1965, when 4,500 kilograms was produced. The high production volume tended to saturate the air filters, with the result that a daily average of of plutonium was detected in stack releases in July 1957. This rose to in December, and by late 1958. A program of filter inspection and replacement was instituted, but daily averages remained high into 1959.