View source for X-10 Graphite Reactor

{{Short description|Decommissioned nuclear reactor in Tennessee}}
{{featured article}}
{{use mdy dates|date=March 2017}}
{{Infobox nuclear reactor
| name        = X-10 Graphite Reactor
| image       = X10 Reactor Face.jpg
| alt         = Two workmen on a movable platform similar to that used by window washers, stick a rod into one of many small holes in the wall in front of them.
| caption     = Workers in the Graphite Reactor use a rod to push fresh uranium slugs into the reactor's concrete loading face.
| headerstyle = background:{{Designation/color|NRHP}}
| concept     = [[Research reactor]] (uranium/graphite)
| design_label= Designed and built by
| design      = [[Metallurgical Laboratory]]
| operation   = 1943 to 1963
| status      = Decommissioned
| fuel        = Metallic natural uranium
| fuel_state  = Solid (pellets)
| spectrum    = [[Thermal-neutron reactor|Thermal]]
| control     = Control rods
| coolant     = Air
| moderator   = [[Nuclear graphite]] (bricks)
| use         = Research
| spectrum_description    = slow
| remarks     = The world's second artificial [[nuclear reactor]].
| module = {{Infobox NRHP
| nrhp_type            = nhl
| location             = [[Oak Ridge National Laboratory]]
| nearest_city         = [[Oak Ridge, Tennessee]]
| coordinates          = {{wikidatacoord|display=inline,title}}
| district_map         = {{Maplink|frame=yes|plain=yes|frame-align=center|frame-width=270|frame-height=180|zoom=6|type=point|description=|marker=industrial}}
| map_caption          = Interactive map highlighting the location of the X-10 Reactor
| area                 = less than {{convert|1|acre|ha}}<ref name="NPS"/>
| built                = 1943
| architect            =
| architecture         =
| designated_nrhp_type = December 21, 1965
| added                = October 15, 1966
| visitation_num       =
| visitation_year      =
| refnum               = 66000720
| mpsub                =
| embed = yes
}}
}}

The '''X-10 Graphite Reactor''' is a decommissioned [[nuclear reactor]] at [[Oak Ridge National Laboratory]] in [[Oak Ridge, Tennessee]]. Formerly known as the '''Clinton Pile''' and '''X-10 Pile''', it was the world's second artificial nuclear reactor (after [[Enrico Fermi]]'s [[Chicago Pile-1]]) and the first intended for continuous operation. It was built during [[World War II]] as part of the [[Manhattan Project]].

While Chicago Pile-1 demonstrated the feasibility of nuclear reactors, the Manhattan Project's goal of producing enough [[plutonium]] for [[atomic bomb]]s required reactors a thousand times as powerful, along with facilities to chemically separate the plutonium bred in the reactors from [[uranium]] and [[fission products]]. An intermediate step was considered prudent. The next step for the plutonium project, codenamed X-10, was the construction of a [[wikt:semi-works|semiworks]] where techniques and procedures could be developed and training conducted. The centerpiece of this was the X-10 Graphite Reactor. It was air-cooled, used [[nuclear graphite]] as a [[neutron moderator]], and pure [[natural uranium]] in metal form for fuel.

Using designs by the [[Metallurgical Laboratory]], [[DuPont]] commenced construction of the plutonium semiworks at the [[Clinton Engineer Works]] in Oak Ridge on February 2, 1943. The reactor [[Criticality (status)|went critical]] on November 4, 1943, and produced its first plutonium in early 1944. The reactor and chemical separation plant provided invaluable experience for engineers, technicians, reactor operators, and safety officials who then moved on to the [[Hanford Site]]. It supplied the [[Los Alamos Laboratory]] with its first significant amounts of plutonium and its first reactor-bred product. Studies of these samples in comparison to those from [[Cyclotron|cyclotrons]] revealed a higher content of [[plutonium-240]], making the gun-type [[Thin Man (nuclear bomb)|Thin Man]] design impossible, leading to the [[Trinity (nuclear test)|Gadget]] and [[Fat Man]] bombs of the now-ubiquitous implosion-type. 

X-10 operated as a plutonium production plant until January 1945, when it was turned over to research activities and the production of radioactive isotopes for scientific, medical, industrial and agricultural uses. In August 1948, it became the first nuclear reactor to produce electricity, lighting a single bulb. It was shut down in 1963 and was designated a [[National Historic Landmark]] in 1965.

==Origins==
The discovery of [[nuclear fission]] by German chemists [[Otto Hahn]] and [[Fritz Strassmann]] in 1938,{{sfn|Rhodes|1986|pp=251–254}} followed by its theoretical explanation (and naming) by [[Lise Meitner]] and [[Otto Frisch]],{{sfn|Rhodes|1986|pp=256–263}} opened up the possibility of a controlled [[nuclear chain reaction]] with [[uranium]]. At [[Columbia University]], [[Enrico Fermi]] and [[Leo Szilard]] began exploring how this might be done.{{sfn|Jones|1985|pp=8–10}} Szilard drafted a [[Einstein–Szilard letter|confidential letter]] to the [[President of the United States]], [[Franklin D. Roosevelt]], explaining the possibility of [[atomic bomb]]s, and warning of the danger of a [[German nuclear weapon project]]. He convinced his old friend and collaborator [[Albert Einstein]] to co-sign it, lending his fame to the proposal.<ref>{{cite web| last = The Atomic Heritage Foundation| title = Einstein's Letter to Franklin D. Roosevelt| url=http://www.mphpa.org/index2.php?option=com_content&do_pdf=1&id=172| access-date = May 26, 2007 |archive-url=https://web.archive.org/web/20121027180511/http://www.mphpa.org/index2.php?option=com_content&do_pdf=1&id=172 |archive-date=October 27, 2012 }}</ref> This resulted in support by the U.S. government for research into nuclear fission,<ref>{{cite web| last = The Atomic Heritage Foundation| title = Pa, this requires action!| url=http://www.mphpa.org/index2.php?option=com_content&do_pdf=1&id=173| access-date = May 26, 2007 |archive-url=https://web.archive.org/web/20121029020707/http://www.mphpa.org/index2.php?option=com_content&do_pdf=1&id=173 |archive-date=October 29, 2012 }}</ref> which became the [[Manhattan Project]].{{sfn|Jones|1985|pp=14–15}}

In April 1941, the [[National Defense Research Committee]] asked [[Arthur Compton]], a [[Nobel Prize in Physics|Nobel-Prize-winning]] physics professor at the [[University of Chicago]], to report on the uranium program. His report, submitted in May 1941, foresaw the prospects of developing [[radiological weapon]]s, [[nuclear propulsion]] for ships, and [[nuclear weapons]] using [[uranium-235]] or the recently discovered [[plutonium]].{{sfn|Hewlett|Anderson|1962|pp=36–38}} In October he wrote another report on the practicality of an atomic bomb.{{sfn|Hewlett|Anderson|1962|pp=46–49}} [[Niels Bohr]] and [[John Archibald Wheeler|John Wheeler]] had theorized that heavy isotopes with even [[atomic number]]s and odd number of neutrons were [[Fissile material|fissile]]. If so, then [[plutonium-239]] was likely to be fissile.{{sfn|Anderson|1975|p=82}}

[[Emilio Segrè]] and [[Glenn Seaborg]] at the [[University of California, Berkeley|University of California]] produced 28 μg of plutonium in the 60-inch [[cyclotron]] there in May 1941 and found that it had 1.7 times the [[thermal neutron]] capture [[Neutron cross section|cross section]] of uranium-235. At the time plutonium-239 had been produced in minute quantities using cyclotrons, but it was not possible to produce large quantities that way.{{sfn|Salvetti|2001|pp=192–193}} Compton discussed with [[Eugene Wigner]] from [[Princeton University]] how plutonium might be produced in a [[nuclear reactor]], and with [[Robert Serber]] how the plutonium produced in a reactor might be separated from uranium.{{sfn|Hewlett|Anderson|1962|pp=46–49}}

The final draft of Compton's November 1941 report made no mention of using plutonium, but after discussing the latest research with [[Ernest Lawrence]], Compton became convinced that a plutonium bomb was also feasible. In December, Compton was placed in charge of the plutonium project,{{sfn|Hewlett|Anderson|1962|pp=50–51}} which was codenamed X-10.{{sfn|Jones|1985|p=91}} Its objectives were to produce reactors to convert uranium to plutonium, to find ways to chemically separate the plutonium from the uranium, and to design and build an atomic bomb.{{sfn|Anderson|1975|p=82}}{{sfn|Hewlett|Anderson|1962|pp=54–55}} It fell to Compton to decide which of the different types of reactor designs the scientists should pursue, even though a successful reactor had not yet been built.{{sfn|Hewlett|Anderson|1962|pp=180–181}} He felt that having teams at Columbia, Princeton, the University of Chicago and the University of California was creating too much duplication and not enough collaboration, and he concentrated the work at the [[Metallurgical Laboratory]] at the University of Chicago.{{sfn|Rhodes|1986|pp=399–400}}

==Site selection==
By June 1942, the Manhattan Project had reached the stage where the construction of production facilities could be contemplated. On June 25, 1942, the [[Office of Scientific Research and Development]] [[S-1 Executive Committee]] deliberated on where they should be located.{{sfn|Jones|1985|pp=46–47}} Moving directly to a megawatt production plant looked like a big step, given that many industrial processes do not easily scale from the laboratory to production size. An intermediate step of building a pilot plant was considered prudent.{{sfn|Oak Ridge National Laboratory|1963|pp=3–4}} For the pilot plutonium separation plant, a site was wanted close to the Metallurgical Laboratory, where the research was being carried out, but for reasons of safety and security, it was not desirable to locate the facilities in a densely populated area like [[Chicago]].{{sfn|Jones|1985|pp=46–47}}

Compton selected a site in the [[Red Gate Woods|Argonne Forest]], part of the [[Forest Preserve District of Cook County]], about {{convert|20|mi}} southwest of Chicago. The full-scale production facilities would be co-located with other Manhattan Project facilities at a still more remote location in Tennessee.{{sfn|Jones|1985|pp=46–47}} Some {{convert|1000|acres}} of land was leased from [[Cook County]] for the pilot facilities, while an {{convert|83000|acre|adj=on}} site for the production facilities was selected at [[Oak Ridge, Tennessee]]. By the S-1 Executive Committee meeting on September 13 and 14, it had become apparent that the pilot facilities would be too extensive for the Argonne site, so instead a research reactor would be built at Argonne, while the plutonium pilot facilities (a [[wikt:semi-works|semiworks]]) would be built at the [[Clinton Engineer Works]] in Tennessee.{{sfn|Jones|1985|pp=67–72}}

The Oak Ridge site was selected on the basis of several criteria. The plutonium pilot facilities needed to be {{convert|2|to|4|mi|spell=in}} from the site boundary and any other installation, in case radioactive [[fission products]] escaped. While security and safety concerns suggested a remote site, it still needed to be near sources of labor, and accessible by road and rail transportation. A mild climate that allowed construction to proceed throughout the year was desirable. Terrain separated by ridges would reduce the impact of accidental explosions, but they could not be so steep as to complicate construction. The [[stratum|substratum]] needed to be firm enough to provide good foundations but not so rocky that it would hinder excavation work. It needed large amounts of electrical power (available from the [[Tennessee Valley Authority]]) and cooling water.{{sfn|Jones|1985|pp=46–47}}{{sfn|Jones|1985|p=69}} Finally, a [[United States Department of War|War Department]] policy held that, as a rule, munitions facilities should not be located west of the [[Sierra Nevada (U.S.)|Sierra]] or [[Cascade Range]]s, east of the [[Appalachian Mountains]], or within {{convert|200|mi}} of the Canadian or Mexican borders.{{sfn|Fine|Remington|1972|pp=134–135}}

In December, it was decided that the plutonium production facilities would not be built at Oak Ridge after all, but at the even more remote [[Hanford Site]] in [[Washington state]]. Compton and the staff at the Metallurgical Laboratory then reopened the question of building the plutonium semiworks at Argonne, but the engineers and management of [[DuPont]], particularly [[Roger Williams (chemist)|Roger Williams]] (the head of its TNX Division, which was responsible for the company's role in the Manhattan Project), did not support this proposal. They felt that there would be insufficient space at Argonne and that there were disadvantages in having a site that was so accessible, as they were afraid that it would permit the research staff from the Metallurgical Laboratory to interfere unduly with the design and construction, which they considered their prerogative.{{sfn|Jones|1985|pp=108–112}} A better location, they felt, would be with the remote production facilities at Hanford. In the end a compromise was reached.{{sfn|Holl|Hewlett|Harris|1997|pp=20–21}} On January 12, 1943, Compton, Williams, and [[Brigadier general (United States)|Brigadier General]] [[Leslie R. Groves, Jr.]], the director of the Manhattan Project, agreed that the semiworks would be built at the Clinton Engineer Works.{{sfn|Hewlett|Anderson|1962|pp=190–193}}

Both Compton and Groves proposed that DuPont operate the semiworks. Williams counter-proposed that the semiworks be operated by the Metallurgical Laboratory. He reasoned that it would primarily be a research and educational facility, and that expertise was to be found at the Metallurgical Laboratory. Compton was shocked;{{sfn|Hewlett|Anderson|1962|pp=190–193}} the Metallurgical Laboratory was part of the University of Chicago, and therefore the university would be operating an industrial facility {{convert|500|mi}} from its main campus. [[James B. Conant]] told him that [[Harvard University]] "wouldn't touch it with a ten-foot pole",{{sfn|Compton|1956|p=172}} but the University of Chicago's Vice President, Emery T. Filbey, took a different view and instructed Compton to accept.{{sfn|Holl|Hewlett|Harris|1997|p=8}} When University President [[Robert Maynard Hutchins|Robert Hutchins]] returned, he greeted Compton with "I see, Arthur, that while I was gone you doubled the size of my university".{{sfn|Compton|1956|p=173}}

==Design==
[[File:Nuclear Reactor Uranium Pile (30502443888).jpg|thumb|Diagram of the reactor]]
[[File:HD.30.623 (10445719914).jpg|thumb|right|Under construction|alt=Building site, with materials lying about]]
The fundamental design decisions in building a reactor are the choice of fuel, coolant and [[neutron moderator]]. The choice of fuel was straightforward; only [[natural uranium]] was available. The decision that the reactor would use [[graphite]] as a neutron moderator caused little debate. Although with [[heavy water]] as moderator the number of neutrons produced for every one absorbed (known as [[Six_factor_formula#Multiplication|''k'' factor]]) was 10 percent more than in the purest graphite, heavy water would be unavailable in sufficient quantities for at least a year.{{sfn|Oak Ridge National Laboratory|1963|pp=3–4, 18}} This left the choice of coolant, over which there was much discussion. A limiting factor was that the fuel slugs would be clad in [[Aluminium|aluminum]], so the operating temperature of the reactor could not exceed  {{convert|200|C}}.{{sfn|Oak Ridge National Laboratory|1963|pp=3–4}} The theoretical physicists in Wigner's group at the Metallurgical Laboratory developed several designs. In November 1942, the DuPont engineers chose [[helium]] gas as the coolant for the production plant, mainly on the basis that it did not absorb neutrons but also because it was inert, which removed the issue of corrosion.{{sfn|Jones|1985|pp=107, 192–193}}

Not everyone agreed with the decision to use helium. Szilard, in particular, was an early proponent of using liquid [[bismuth]]; but the major opponent was Wigner, who argued forcefully in favor of a water-cooled reactor design. He realized that since water absorbed neutrons, ''k'' would be reduced by about 3 percent, but he had sufficient confidence in his calculations that the water-cooled reactor would still be able to achieve [[Criticality (status)|criticality]]. From an engineering perspective, a water-cooled design was straightforward to design and build, while helium posed technological problems. Wigner's team produced a preliminary report on water cooling, designated CE-140 in April 1942, followed by a more detailed one, CE-197, titled "On a Plant with Water Cooling", in July 1942.{{sfn|Weinberg|1994|pp=22–24}}

Fermi's [[Chicago Pile-1]] reactor, constructed under the west viewing stands of the original [[Stagg Field]] at the University of Chicago, "went critical" on December 2, 1942. This graphite-moderated reactor only generated up to 200 W, but it demonstrated that ''k'' was higher than anticipated. This removed most of the objections to air-cooled and water-cooled reactor designs, and it greatly simplified other aspects of the design. Wigner's team submitted blueprints of a water-cooled reactor to DuPont in January 1943. By this time, the concerns of DuPont's engineers about the corrosiveness of water had been overcome by the mounting difficulties of using helium, and all work on helium was terminated in February. At the same time, air cooling was chosen for the reactor at the pilot plant.{{sfn|Jones|1985|pp=191–193}} Since it would be of a quite different design from the production reactors, the X-10 Graphite Reactor lost its value as a prototype, but its value as a working pilot facility remained, providing plutonium needed for research.{{sfn|Jones|1985|pp=204–205}} It was hoped that problems would be found in time to deal with them in the production plants. The semiworks would also be used for training and for developing procedures.{{sfn|Oak Ridge National Laboratory|1963|pp=3–4}}

==Construction==
Although the design of the reactor was not yet complete, DuPont began construction of the plutonium semiworks on February 2, 1943,{{sfn|Hewlett|Anderson|1962|p=207}} on an isolated {{convert|112|acre|ha|1|adj=on}} site in Bethel Valley about {{convert|10|mi}} southwest of Oak Ridge, officially known as the X-10 area. The site included research laboratories, a chemical separation plant, a waste storage area, a training facility for Hanford staff, and administrative and support facilities that included a laundry, cafeteria, first aid center, and fire station. Because of the subsequent decision to construct water-cooled reactors at Hanford, only the chemical separation plant operated as a true pilot.{{sfn|Jones|1985|pp=204–206}}{{sfn|Manhattan District|1947|pp=2.4–2.6}} The semiworks eventually became known as the Clinton Laboratories and was operated by the University of Chicago as part of the Metallurgical Project.{{sfn|Manhattan District|1947|p=S3}}

[[File:HD.30.645 (10445870426).jpg|thumb|left|X-10 under construction|alt=Building site. A chimney has been erected and scaffolding has gone up.]]
Construction work on the reactor had to wait until DuPont had completed the design. Excavation commenced on April 27, 1943. A large pocket of soft clay was soon discovered, necessitating additional foundations.{{sfn|Hewlett|Anderson|1962|pp=207–208}} Further delays occurred due to wartime difficulties in procuring building materials. There was an acute shortage of both common and skilled labor; the contractor had only three-quarters of the required workforce, and there was high turnover and absenteeism, mainly the result of poor accommodations and difficulties in commuting. The township of Oak Ridge was still under construction, and barracks were built to house workers. Special arrangements with individual workers increased their morale and reduced turnover. Furthermore, there was unusually heavy rainfall, with {{convert|9.3|in}} falling in July 1943, more than twice the average of {{convert|4.3|in}}.{{sfn|Jones|1985|pp=204–206}}{{sfn|Manhattan District|1947|pp=2.7–2.8}}

Some {{convert|700|ST}} of graphite blocks were purchased from [[National Carbon Company|National Carbon]]. The construction crews began stacking them in September 1943. Cast uranium [[Semi-finished casting products|billets]] came from Metal Hydrides, [[Mallinckrodt]] and other suppliers. These were extruded into cylindrical slugs and then canned.{{sfn|Hewlett|Anderson|1962|pp=209–210}} The fuel slugs were canned to protect the uranium metal from [[corrosion]] that would occur if it came into contact with water and to prevent the venting of gaseous radioactive fission products that might be formed when they were irradiated. Aluminum was chosen because it transmitted heat well but did not absorb too many neutrons.{{sfn|Smyth|1945|pp=146–147}} [[Alcoa]] started canning on June 14, 1943. [[General Electric]] and the Metallurgical Laboratory developed a new welding technique to seal the cans airtight, and the equipment for this was installed in the production line at Alcoa in October 1943.{{sfn|Hewlett|Anderson|1962|pp=209–210}}

Construction commenced on the pilot separation plant before a chemical process for separating plutonium from uranium had been selected. Not until May 1943 would DuPont managers decide to use the [[bismuth phosphate process]] in preference to one using [[Lanthanum trifluoride|lanthanum fluoride]].{{sfn|Jones|1985|p=194}} The bismuth phosphate process was devised by [[Stanley G. Thompson]] at the [[University of California, Berkeley|University of California]].{{sfn|Hewlett|Anderson|1962|p=185}} Plutonium had two oxidation states; a [[tetravalent]] (+4) state, and [[hexavalent]] (+6) state, with different chemical properties.{{sfn|Hewlett|Anderson|1962|p=89}} Bismuth phosphate ({{chem|Bi|P|O|4}}) was similar in its crystalline structure to plutonium phosphate,{{sfn|Gerber|1996|p=4-1}} and plutonium would be carried with bismuth phosphate in a solution while other elements, including uranium, would be precipitated. The plutonium could then be precipitated from the solution by changing its oxidation state.{{sfn|Gerber|1996|p=4-7}} The plant consisted of six cells, separated from each other and the control room by thick concrete walls. The equipment was operated from the control room by remote control due to the radioactivity produced by fission products.{{sfn|Manhattan District|1947|p=S3}} Work was completed on November 26, 1943,{{sfn|Manhattan District|1947|p=S2}} but the plant could not operate until the reactor started producing irradiated uranium slugs.{{sfn|Jones|1985|pp=204–206}}

==Operation==
[[File:GraphiteReactor.jpg|thumb|right|upright|Loading fuel slugs|alt=Two workmen in overalls put a rod into a hole on the reactor face]]
The X-10 Graphite Reactor was the world's second artificial nuclear reactor after Chicago Pile-1 and was the first reactor designed and built for continuous operation.<ref name=ORNLM&C /> It consisted of a huge block, {{convert|24|ft|m}} long on each side, of [[nuclear graphite]] cubes, weighing around {{convert|1500|ST}}, that acted as a moderator. They were surrounded by {{convert|7|ft|m|spell=in}} of high-density concrete as a radiation shield.{{sfn|Jones|1985|pp=204–206}} In all, the reactor was {{convert|38|ft}} wide, {{convert|47|ft}} deep and {{convert|32|ft}} high.<ref name="NPS" /> There were 36 horizontal rows of 35 holes. Behind each was a metal channel into which uranium fuel slugs could be inserted.{{sfn|Manhattan District|1947|p=S4}} An elevator provided access to those higher up. Only 800 (~64%) of the channels were ever used.<ref name="NPS" />

The reactor used [[cadmium]]-clad steel [[control rods]]. Made from neutron-absorbing cadmium, these could restrict or halt the reaction. Three {{convert|8|ft|adj=on}} rods penetrated the reactor vertically, held in place by a clutch to form the [[scram]] system. They were suspended from steel cables that were wound around a drum and held in place by an electromagnetic [[clutch]]. If power was lost, they would drop into the reactor, halting it. The other four rods were made of [[boron]] steel and horizontally penetrated the reactor from the north side. Two of them, known as "shim" rods, were hydraulically controlled. Sand-filled [[hydraulic accumulator]]s could be used in the event of a power failure. The other two rods were driven by electric motors.<ref name="NPS"/>

The cooling system consisted of three electric fans running at {{Convert|55000|cuft/min}}. Because it was cooled using outside air, the reactor could be run at a higher power level on cold days.<ref name="NPS"/>{{sfn|Manhattan District|1947|p=S5}} After going through the reactor, the air was filtered to remove radioactive particles larger than {{convert|0.00004|in}} in diameter. This took care of over 99 percent of the radioactive particles. It was then vented through a {{convert|200|ft|adj=on}} chimney.<ref name="NPS" />  The reactor was operated from a control room in the southeast corner on the second floor.<ref name="NPS"/>

In September 1942, Compton asked physicist [[Martin D. Whitaker]] to form a skeleton operating staff for X-10.{{sfn|Jones|1985|p=209}} Whitaker became the inaugural director of the Clinton Laboratories,{{sfn|Hewlett|Anderson|1962|pp=207–208}} as the semiworks became officially known in April 1943.{{sfn|Jones|1985|p=204}} The first permanent operating staff arrived from the Metallurgical Laboratory in Chicago in April 1943, by which time DuPont began transferring its technicians to the site. They were augmented by 100 technicians in uniform from the Army's [[Special Engineer Detachment]]. By March 1944, there were some 1,500 people working at X-10.{{sfn|Jones|1985|p=208}}

[[File:Exterior of the Graphite Reactor at the X-10 site in Oak Ridge in 1950.jpg|thumb|left|Exterior of the Graphite Reactor at the X-10 site in Oak Ridge in 1950|alt=A large four-story building. The chimney is in the background. There are power poles and power lines in front.]]
Supervised by Compton, Whitaker, and Fermi, the reactor went critical on November 4, 1943, with about {{convert|30|ST}} of uranium. A week later the load was increased to {{convert|36|ST}}, raising its power generation to 500&nbsp;kW, and by the end of the month the first 500&nbsp;mg of plutonium was created.{{sfn|Hewlett|Anderson|1962|p=211}} The reactor normally operated around the clock, with 10-hour weekly shutdowns for refueling. During startup, the safety rods and one shim rod were completely removed. The other shim rod was inserted at a predetermined position. When the desired power level was reached, the reactor was controlled by adjusting the partly inserted shim rod.<ref name="NPS"/>

The first batch of canned slugs to be irradiated was received on December 20, 1943, allowing the first plutonium to be produced in early 1944.{{sfn|Manhattan District|1947|p=S7}} The slugs used pure metallic natural uranium, in air-tight aluminum cans {{convert|4.1|in}} long and {{convert|1|in}} in diameter. Each channel was loaded with between 24 and 54 fuel slugs. In its later life the reactor was operated with as much as {{convert|54|ST}}. To load a channel, the radiation-absorbing shield plug was removed, and the slugs inserted manually in the front (east) end with long rods. To unload them, they were pushed all the way through to the far (west) end, where they fell onto a [[neoprene]] slab and fell down a chute into a {{convert|20|ft|m|adj=mid|-deep}} pool of water that acted as a radiation shield.<ref name="NPS" /> Following weeks of underwater storage to allow for [[Radioactive decay|decay in radioactivity]], the slugs were delivered to the chemical separation building.<ref name="DOE">{{cite web |url=http://energy.gov/management/x-10-graphite-reactor |title=X-10 Graphite Reactor |website=Office of Management |publisher=[[United States Department of Energy]] |access-date=December 13, 2015 }}</ref>

[[File:HD.5A.005 (13406538825).jpg|thumb|right|Reactor controls|alt=A control panel with lots of switches and meters]]
By February 1944, the reactor was irradiating a ton of uranium every three days. Over the next five months, the efficiency of the separation process was improved, with the percentage of plutonium recovered increasing from 40 to 90 percent. Modifications over time raised the reactor's power to 4,000&nbsp;kW in July 1944.{{sfn|Jones|1985|p=209}} The effect of the [[neutron poison]] [[xenon-135]], one of many fission products produced from the uranium fuel, was not detected during the early operation of the X-10 Graphite Reactor. Xenon-135 subsequently caused problems with the startup of the Hanford [[B Reactor]] that nearly halted the plutonium project.{{sfn|Hewlett|Anderson|1962|pp=306–307}}

The X-10 semiworks operated as a plutonium production plant until January 1945, when it was turned over to research activities. By this time, 299 batches of irradiated slugs had been processed.{{sfn|Jones|1985|p=209}} A radioisotope building, a steam plant, and other structures were added in April 1946 to support the laboratory's peacetime educational and research missions. All work was completed by December 1946, adding another $1,009,000 (equivalent to ${{formatprice|{{inflation|US-GDP|1009000|1946}}}} in {{inflation-year|US-GDP}}{{inflation-fn|US-GDP}}) to the cost of construction at X-10, and bringing the total cost to $13,041,000 (equivalent to ${{formatprice|{{inflation|US-GDP|13041000|1946}}}} in {{inflation-year|US-GDP}}{{inflation-fn|US-GDP}}).{{sfn|Manhattan District|1947|p=S3}} Operational costs added another $22,250,000 (equivalent to ${{formatprice|{{inflation|US-GDP|22250000|1946}}}} in {{inflation-year|US-GDP}}{{inflation-fn|US-GDP}}).{{sfn|Manhattan District|1947|p=S4}}

X-10 supplied the [[Los Alamos Laboratory]] with the first significant samples of plutonium. Studies of these by [[Emilio G. Segrè]] and his P-5 Group at Los Alamos revealed that it contained impurities in the form of the [[isotope]] [[plutonium-240]], which has a far higher [[spontaneous fission]] rate than plutonium-239. This meant that it would be highly likely that a plutonium [[gun-type nuclear weapon]] would [[predetonation|predetonate]] and blow itself apart during the initial formation of a critical mass.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=228}} The Los Alamos Laboratory was thus forced to turn its development efforts to creating an [[implosion-type nuclear weapon]]—a far more difficult feat.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=240–244}}

The X-10 chemical separation plant also verified the bismuth-phosphate process that was used in the full-scale separation facilities at Hanford. The reactor and chemical separation plant provided invaluable experience for engineers, technicians, reactor operators, and safety officials who then moved on to the Hanford Site.<ref name="DOE" />

==Peacetime use==
[[File:X-10 Reactor 05.jpg|thumb|Loading face, 2019. The model steam engine is in the acrylic box at the lower left.|alt=Two workmen on a movable platform similar to that used by window washers, in front of a wall with arrays of holes and many wires running across it. A sign says "Graphite Reactor loading face".]]
After the war ended, the graphite reactor became the first facility in the world to produce radioactive isotopes for peacetime use.<ref name="NPS"/>{{sfn|Creager|2013|p=68}} On August 2, 1946, [[Oak Ridge National Laboratory]] director Eugene Wigner presented a small container of [[carbon-14]] to the director of the Barnard Free Skin and Cancer Hospital, for medical use at the hospital in [[St. Louis, Missouri]]. Subsequent shipments of radioisotopes, primarily [[iodine-131]], [[phosphorus-32]], carbon-14, and molybdenum-99/[[technetium-99m]], were for scientific, medical, industrial and agricultural uses.<ref name=ACS/>

In August 1948, the reactor was used to produce the first electricity derived from nuclear power. Uranium slugs within an aluminum tube were irradiated within the reactor core. Water was circulated through the tube by means of an automatic feedwater system to generate steam. This steam was fed to a [[model steam engine]], a [[Jensen Steam Engines]] #50, which drove a small generator that powered a single bulb. The engine and generator are on display at the reactor loading face, just below the staircase leading to the loading platform.<ref>{{cite web |last1=Garceau |first1=Gil |title=World's First Nuclear Power Generated Electricity from Jensen #50 on the X 10 Graphite Reactor 1948 |url=https://www.youtube.com/watch?v=FzAjO5_SyTU |website=YouTube |date=January 25, 2015 |access-date=4 April 2022}}</ref>

The X-10 Graphite Reactor was shut down on November 4, 1963, after 20 years of use.{{sfn|Oak Ridge National Laboratory|1963|p=1}} It was designated a [[National Historic Landmark]] on December 21, 1965,<ref name="NPS">{{Cite book|title=National Register of Historic Places Inventory-Nomination: X-10 Reactor, Graphite Reactor|url={{NHLS url|id=66000720}} |format=pdf|date=December 8, 1975 |first=Polly M. |last=Rettig |publisher=National Park Service}} and {{NHLS url|id=66000720|title=''Accompanying three photos, interior, undated''|photos=y}}&nbsp;{{small|(32&nbsp;KB)}}</ref><ref name="nhlsum"/> and added to the [[National Register of Historic Places]] on October 15, 1966.<ref name="nhlsum">{{cite web|url=http://tps.cr.nps.gov/nhl/detail.cfm?ResourceId=541&ResourceType=Structure |archive-url=https://web.archive.org/web/20150509002348/http://tps.cr.nps.gov/nhl/detail.cfm?ResourceId=541&ResourceType=Structure |archive-date=May 9, 2015 |title=X-10 Reactor, Oak Ridge National Laboratory |access-date=October 7, 2008|work=National Historic Landmarks Program|publisher=National Park Service}}</ref> In 1969 the [[American Society for Metals]] listed it as a landmark for its contributions to the advancement of [[materials science]] and technology,<ref name=ORNLM&C>{{cite web |url=http://web.ornl.gov/sci/psd/mst/pdf/mchistory.pdf |title=ORNL Metals and Ceramics Division History, 1946–1996 |publisher=Oak Ridge National Laboratory |id=ORNL/M-6589 |access-date=January 25, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150128132636/http://web.ornl.gov/sci/psd/mst/pdf/mchistory.pdf |archive-date=January 28, 2015 |df=mdy-all }}</ref> and in 2008 it was designated as a [[National Historic Chemical Landmark]] by the [[American Chemical Society]].<ref name=ACS>{{cite web |url=http://www.acs.org/content/acs/en/pressroom/newsreleases/2008/february/peacetime-use-of-radioisotopes-at-oak-ridge-cited-as-chemical-landmark.html |title=Peacetime use of radioisotopes at Oak Ridge cited as Chemical Landmark |publisher=American Chemical Society |date=February 25, 2008 |access-date=December 12, 2015}}</ref> The control room and reactor face are accessible to the public during scheduled tours offered through the [[American Museum of Science and Energy]].<ref>{{cite web |url=https://www.ornl.gov/content/tours |title=Public Tours |publisher=[[Oak Ridge National Laboratory]] |access-date=December 12, 2015 |url-status=live |archive-url=https://web.archive.org/web/20151222161041/https://www.ornl.gov/content/tours |archive-date=December 22, 2015}}</ref>

==Similar reactors==
The [[Brookhaven National Laboratory]] (BNL) Graphite Research Reactor was the first nuclear reactor to be constructed in the United States following World War II.<ref>{{cite journal|journal=Popular Science |volume=154 |issue=4 |url = https://books.google.com/books?id=eSQDAAAAMBAJ&pg=RA1-PA121|date = April 1, 1949 |first = Martin|last = Mann|title=U.S. lights new atomic pile for peace|issn=0161-7370}}</ref> Led by [[Lyle Benjamin Borst]], the reactor construction began in 1947 and reached criticality on August 22, 1950. The reactor consisted of a {{convert|700|ST|adj=on}}, {{convert|25|ft|m|adj=on}} cube of graphite fueled by natural uranium.<ref>{{cite news|title = Brookhaven Lab's Old Reactor Is Finally Being Dismantled|url = https://www.nytimes.com/2000/02/13/nyregion/brookhaven-lab-s-old-reactor-is-finally-being-dismantled.html|newspaper = The New York Times|date = February 13, 2000|access-date = February 13, 2016|issn = 0362-4331|first = Valerie|last = Cotsalas}}</ref> Its primary mission was applied nuclear research in medicine, biology, chemistry, physics and nuclear engineering.<ref>{{cite web|title = Brookhaven Graphite Research Reactor History |url = http://www.bnl.gov/bnlweb/history/BGRR.asp|access-date = February 13, 2016 |archive-url = https://web.archive.org/web/20130314084539/http://www.bnl.gov/bnlweb/history/BGRR.asp|archive-date = March 14, 2013 |publisher = Brookhaven National Laboratory}}</ref> One of the most significant discoveries at this facility was the development of production of [[molybdenum-99]]/technetium-99m, used today in tens of millions of medical diagnostic procedures annually, making it the most commonly used medical radioisotope. The BNL Graphite Research Reactor was shut down in 1969 and fully decommissioned in 2012.<ref>{{cite web|title = Brookhaven Lab Completes Decommissioning of Graphite Research Reactor: Reactor core and associated structures successfully removed; waste shipped offsite for disposal |date= September 1, 2012 |url = http://energy.gov/em/articles/brookhaven-lab-completes-decommissioning-graphite-research-reactor |website=Office of Environmental Management |publisher=[[United States Department of Energy]] |access-date = February 13, 2016}}</ref>

When Britain began planning to build nuclear reactors to produce plutonium for weapons in 1946, it was decided to build a pair of air-cooled graphite reactors similar to the X-10 Graphite Reactor at [[Windscale]]. Natural uranium was used as [[enriched uranium]] was not available, and similarly graphite was chosen as a neutron moderator because [[beryllia]] was toxic and hard to manufacture, while heavy water was unavailable.{{sfn|Gowing|Arnold|1974|pp=277–278}} Use of water as a coolant was considered, but there were concerns about the possibility of a catastrophic [[nuclear meltdown]] in the densely populated British Isles if the cooling system failed.{{sfn|Arnold|1992|pp=9–11}} Helium was again the preferred choice as a coolant gas, but the main source of it was the United States, and under the 1946 [[McMahon Act]], the United States would not supply it for nuclear weapons production,{{sfn|Gowing|Arnold|1974|pp=285–286}} so in the end air cooling was chosen.{{sfn|Gowing|Arnold|1974|p=404}} Construction began in September 1947, and the two reactors became operational in October 1950 and June 1951.{{sfn|Arnold|1992|p=15}} Both were decommissioned after the disastrous [[Windscale fire]] in October 1957.{{sfn|Arnold|1992|pp=122–123}} They were the last major air-cooled plutonium-producing reactors; the UK's follow-on [[Magnox]] and [[Advanced gas-cooled reactor|AGR]] designs used [[carbon dioxide]] instead.{{sfn|Hill|2013|pp=18–20}}

{{As of|2016}}, another reactor of similar design to the X-10 Graphite Reactor is still in operation, the Belgian BR-1 reactor of the [[SCK•CEN]], located in [[Mol, Belgium]].<ref>{{Cite web|title = Belgian Reactor 1 – BR1 |url = http://science.sckcen.be/en/Facilities/BR1 |website = SCK•CEN Science Platform |publisher=Belgian Nuclear Research Centre |access-date = February 12, 2016}}</ref> Financed through the Belgian uranium export tax, and built with the help of British experts,{{sfn|Buch|Vandenlinden|1995|p= 120}} the 4 MW research reactor went critical on May 11, 1956.<ref>{{Cite journal|title = The Negotiation of the Belgian Uranium Export Tax of 1951|journal = Revue Belge de Philologie et d'Histoire|pages = 320–351|volume = 68|issue = 2|doi = 10.3406/rbph.1990.3713|first = Jonathan E.|last = Helmreich|year = 1990|url = http://www.persee.fr/docAsPDF/rbph_0035-0818_1990_num_68_2_3713.pdf}}</ref><ref>{{Cite journal|title = U.S. Foreign Policy and the Belgian Congo in the 1950s|journal = Historian|date = 1996|issn = 1540-6563|pages = 315–328|volume = 58|issue = 2|doi = 10.1111/j.1540-6563.1996.tb00951.x|language = en|first = Jonathan E.|last = Helmreich}}</ref> It is used for scientific purposes, such as [[neutron activation analysis]], neutron physics experiments, calibration of nuclear measurement devices and the production of [[Doping (semiconductor)#Neutron transmutation doping|neutron transmutation doped silicon]].<ref>{{cite web |url=http://www.sckcen.be/en/Our-Research/Research-facilities/BR1-Belgian-Reactor-1 |title=BR1 – Belgian Reactor 1 |website = SCK•CEN |publisher=Belgian Nuclear Research Centre |access-date=October 8, 2008 |archive-url=https://web.archive.org/web/20130704085931/http://www.sckcen.be/en/Our-Research/Research-facilities/BR1-Belgian-Reactor-1 |archive-date=July 4, 2013}}</ref><ref>{{Cite web|title = 2006 → 50th anniversary BR1 |year=2006 |publisher=Belgian Nuclear Research Centre |language=fr |url = http://www.sckcen.be/SCKCEN_Information_Package_2006/CDROM_files/br1/historybrochure.pdf |access-date = December 17, 2015 |archive-url = https://web.archive.org/web/20060816043317/http://www.sckcen.be/SCKCEN_Information_Package_2006/CDROM_files/br1/historybrochure.pdf|archive-date = August 16, 2006}}</ref>

==Notes==
{{Reflist}}

==References==
{{refbegin}}
* {{cite book| last = Arnold | first = Lorna |author-link=Lorna Arnold | title = Windscale 1957: Anatomy of a Nuclear Accident | publisher = Macmillan | year = 1992 | isbn = 978-0-333-65036-3 }}
* {{cite book |last=Anderson |first=Herbert L. |author-link=Herbert L. Anderson |contribution=Assisting Fermi |pages=66–104 |editor-first=Jane |editor-last=Wilson |title=All In Our Time: The Reminiscences of Twelve Nuclear Pioneers |location=Chicago |year=1975 |publisher=Bulletin of the Atomic Scientists |oclc=1982052 }}
* {{Cite book|title = L'uranium, la Belgique et les puissances: marché de dupes, ou, chef d'œuvre diplomatique?|url = https://books.google.com/books?id=j9Uo0D8nnVMC&q=taxe%20uranium%20belgique&pg=PA120|publisher = De Boeck Supérieur|date = 1995|isbn = 978-2-8041-1993-5|language = fr|first1 = Pierre|last1 = Buch|first2 = Jacques|last2 = Vandenlinden|page = 120}}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite book |last=Compton |first=Arthur |author-link=Arthur Compton |year=1956 |title=Atomic Quest |url=https://archive.org/details/atomicquestperso0000comp |url-access=registration |location=New York |publisher=Oxford University Press |oclc=173307 }}
* {{cite book|last=Creager|first=Angela N. H.|title=Life Atomic: A History of Radioisotopes in Science and Medicine|url=https://books.google.com/books?id=WdpAAAAAQBAJ&pg=PA68|year=2013|publisher=University of Chicago Press|isbn=978-0-226-01794-5}}
* {{cite book |last1=Fine |first1=Lenore |last2=Remington |first2=Jesse A. |title=The Corps of Engineers: Construction in the United States |publisher=United States Army Center of Military History |url=http://www.history.army.mil/html/books/010/10-5/CMH_Pub_10-5.pdf |access-date=August 25, 2013 |location=Washington, D.C. |year=1972 |oclc=834187 |archive-date=February 1, 2017 |archive-url=https://web.archive.org/web/20170201142645/https://history.army.mil/html/books/010/10-5/CMH_Pub_10-5.pdf |url-status=dead }}
* {{cite book |last=Gerber |first=Michele |title=Plutonium Production Story at the Hanford Site: Processes and Facilities History |date=June 1996 |id=HC-MR-0521 |location=Washington, D.C. |oclc=68435718 |publisher=[[United States Department of Energy]] |doi=10.2172/664389 |url=https://www.osti.gov/scitech/servlets/purl/664389-jAx4J1/webviewable/PlutoniumproductionstoryattheHanfordsite:processesandfacilitieshistory.pdf |access-date=17 April 2017 }}
* {{cite book |last1=Gowing |first1=Margaret |author-link=Margaret Gowing |last2=Arnold |first2=Lorna |author-link2=Lorna Arnold |title=Independence and Deterrence: Britain and Atomic Energy 1945–52, Volume II: Policy Execution |location=London |year=1974 |publisher=Macmillan }}
* {{cite book |last1=Hewlett |first1=Richard G. |author-link=Richard G. Hewlett |last2=Anderson |first2=Oscar E. |title=The New World, 1939–1946 |location=University Park, Pennsylvania |publisher=Pennsylvania State University Press |year=1962 |url=https://www.governmentattic.org/5docs/TheNewWorld1939-1946.pdf |access-date=26 March 2013 |isbn=978-0-520-07186-5 |oclc=637004643 }}
* {{cite book |last=Hill |first=C. N. |title=An Atomic Empire : a Technical History of the Rise and Fall of the British Atomic Energy Programme |location=London |publisher=Imperial College Press |year=2013 |isbn=978-1-908977-41-0 |oclc=857066061 }}
* {{cite book |last1=Hoddeson |first1=Lillian |author-link=Lillian Hoddeson |first2=Paul W. |last2=Henriksen |first3=Roger A. |last3=Meade |first4=Catherine L. |last4=Westfall |author4-link=Catherine Westfall |title=Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945 |location=New York |publisher=Cambridge University Press |year=1993 |isbn=978-0-521-44132-2 |oclc=26764320 |url-access=registration |url=https://archive.org/details/criticalassembly0000unse }}
* {{cite book |last1=Holl |first1=Jack M. |title=Argonne National Laboratory, 1946–96 |first2=Richard G. |last2=Hewlett |author-link2=Richard G. Hewlett |first3=Ruth R. |last3=Harris |publisher=University of Illinois Press |location=Urbana, Illinois |year=1997 |isbn=978-0-252-02341-5  }}
* {{cite book |last=Jones |first=Vincent |title=Manhattan: The Army and the Atomic Bomb |publisher=United States Army Center of Military History |location=Washington, D.C. |year=1985 |url=http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf |access-date=25 August 2013 |oclc=10913875 |archive-date=October 7, 2014 |archive-url=https://web.archive.org/web/20141007074359/http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf |url-status=dead }}
* {{cite book |url=http://www.osti.gov/includes/opennet/includes/MED_scans/Book%20IV%20-%20%20Pile%20Project%20X-10%20-%20Volume%202%20-%20Research%20-%20Part%20II.pdf |author=Manhattan District |title=Manhattan District History, Book IV, Volume 2 – Pile Project X-10 – Clinton Laboratories |publisher=Manhattan District |year=1947 |location=Washington, D.C. }}
* {{cite book |author=Oak Ridge National Laboratory |year=1963 |title=ONRL Graphite Reactor |url=http://web.ornl.gov/info/reports/1963/3445605702923.pdf |access-date=December 13, 2015 |archive-url=https://web.archive.org/web/20170211214401/http://web.ornl.gov/info/reports/1963/3445605702923.pdf |archive-date=February 11, 2017 |url-status=dead }}
* {{cite book |last=Rhodes |first=Richard |author-link=Richard Rhodes |title=The Making of the Atomic Bomb |year=1986 |publisher=Simon & Schuster |location=London |isbn=978-0-671-44133-3|title-link=The Making of the Atomic Bomb }}
* {{cite book |last=Salvetti |first=Carlo |contribution=The Birth of Nuclear Energy: Fermi's Pile |pages=[https://archive.org/details/enricofermihiswo0000unse/page/177 177–203] |editor-last=Bernardini |editor-first=C. |editor2-first=Luisa |editor2-last=Bonolis |year=2001 |title=Enrico Fermi: His Work and Legacy |location=Bologna |publisher=Società Italiana di Fisica: Springer |isbn=978-88-7438-015-2 |oclc=56686431 |url=https://archive.org/details/enricofermihiswo0000unse/page/177 }}
* {{cite book | last =Smyth | first =Henry DeWolf | author-link =Henry DeWolf Smyth | url =https://books.google.com/books?id=gp2aAAAAIAAJ | title =Atomic Energy for Military Purposes; the Official Report on the Development of the Atomic Bomb under the Auspices of the United States Government, 1940–1945 | location =Princeton | publisher =Princeton University Press | year =1945 | isbn =978-0-8047-1722-9 }}
* {{cite book |last=Weinberg |first=Alvin |author-link=Alvin Weinberg |title=The First Nuclear Era: The Life and Times of a Technological Fixer |location=New York |publisher=AIP Press |year=1994 |isbn=978-1-56396-358-2 }}
{{refend}}

==Further reading==
{{refbegin}}
* {{cite journal|last1=Snell|first1=Arthur H.|last2=Weinberg|first2=Alvin M.|title=History and accomplishments of the Oak Ridge Graphite Reactor|journal=Physics Today|volume=17|issue=8|year=1964|pages=32|issn=0031-9228|doi=10.1063/1.3051739|bibcode=1964PhT....17h..32S |ref=none}}
{{refend}}

==External links==
{{Commons category|X-10 Graphite Reactor}}
* {{cite web |url=http://www.ornl.gov/info/news/cco/graphite.htm |title=ORNL webpage about the Graphite Reactor |publisher=[[Oak Ridge National Laboratory]] |archive-url=https://web.archive.org/web/20100112171753/http://www.ornl.gov/info/news/cco/graphite.htm |archive-date=January 12, 2010 }}
* {{cite web |url=https://www.ornl.gov/content/tours |title=Public Tours|publisher=[[Oak Ridge National Laboratory]] |access-date=December 12, 2015}}
* {{NRISref|2008a|dateform=mdy|refnum=66000720|name=X-10 Reactor, Oak Ridge National Laboratory}}
{{DoE|article=X-10 Graphite Reactor |url=http://energy.gov/management/x-10-graphite-reactor|access-date=December 13, 2015}}
{{Oak Ridge National Laboratory|state=expanded}}
{{Manhattan Project}}
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