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Weldon Spring Site
Interpretive Center Online Tour

Tribute to the Mallinckrodt Uranium Workers

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Timeline of the Nuclear Age This timeline focuses on world events relating to the nuclear age and also presents events significant to the St. Louis area Uranium Workers.


December: Two German scientists, Otto Hahn and Fritz Strassman, demonstrate nuclear fission.


August: Albert Einstein sends a letter to President Roosevelt informing him of German atomic research and the potential for a bomb.  This letter prompts Roosevelt to form a special committee to investigate the military implications of atomic research.


April: Dr. Arthur Holly Compton, a physicist from the University of Chicago meets with Edward J. Mallinckrodt to ask if Mallinckrodt Chemical Works (MCW) would sign onto a top secret project purifying uranium for the making of the Atomic Bomb.  Mallinckrodt agrees.

Under contracts with the Manhattan Engineering District and the U.S. Atomic Energy Commission (AEC), the Destrehan Street Refinery and Metal Plant (later Mallinckrodt Chemical Works) processes various forms of uranium compounds at a facility in downtown St. Louis.

September: The Manhattan Project is formed to secretly build the atomic bomb before the Germans.

December: Enrico Fermi demonstrates the first self-sustaining nuclear chain reaction in a lab under the squash court at the University of Chicago using uranium purified by MCW.  Soon after, a complex of top-secret nuclear production and research facilities are built by the Manhattan Project across the country.


July: The United States explodes the first atomic device at a site near Alamogordo, New Mexico.

August: The United States drops atomic bombs on Hiroshima and Nagasaki.  Japan surrenders.


July: The Atomic Energy Act (AEA) is passed, establishing the Atomic Energy Commission (AEC).  The AEC replaces the Manhattan Project on December 31, 1946.  The AEA places further development of nuclear technology under civilian (not military) control.

August: An AEC facility in Oak Ridge, Tennessee ships the first nuclear reactor-produced radioisotopes for civilian use to the Barnard Cancer Hospital in St. Louis.  After World War II, Oak Ridge turns out numerous inexpensive radioactive compounds for medical diagnosis and treatment, and for research and industrial applications.


August: The Soviet Union detonates its first atomic device.


December:  The first usable electricity from nuclear fission is produced at the National Reactor Station, later called the Idaho National Engineering Laboratory.


January: The first nuclear submarine, the U.S.S. Nautilus, is launched.

August: The Atomic Energy Act of 1954 is passed to promote the peaceful uses of nuclear energy through private enterprise and to implement President Eisenhower's Atoms for Peace Program.


November:  Soviet Premier Nikita Khrushchev tells the West, "History is on our side.  We will bury you."


June: Operations begin at the Weldon Spring Uranium Feed Materials Plant, built outside of Weldon Spring, Missouri and operated by Mallinckrodt Chemical Works for the Atomic Energy Commission.  Operations included assaying of uranium ore concentrate (‘yellowcake’) and production of uranium metal.  Operations at the Mallinckrodt Destrehan Street facility in St. Louis end.

July: The United Nations International Atomic Energy Agency (IAEA) is created.  The agency inspects nuclear reactors and plants to ensure they are being run for peaceful purposes.

September: The United States sets off the first underground nuclear test in a mountain tunnel in the remote desert 100 miles from Las Vegas.

December: The first U.S. large-scale nuclear power plant begins operating in Shippingport, Pennsylvania.

The large number of utility orders for nuclear power reactors makes nuclear power a commercial reality in the United States.


January: In his inauguration speech, President Kennedy says, "Let every nation know, whether it wishes us well or ill, that we shall pay any price, bear any burden, meet any hardship, support any friend, oppose any foe to assure the survival and success of liberty."

April: The Central Intelligence Agency-backed invasion of Cuba at the Bay of Pigs fails.

August: The Berlin Wall is erected between West and East Berlin.


October: U.S. reconnaissance discovers Soviet missiles in Cuba.  The United States blockades Cuba for 13 days until the Soviet Union agrees to remove its missiles.  The U.S. also agrees to remove its missiles from Turkey.


August: The United States and Soviet Union sign the Limited Test Ban Treaty, which prohibits underwater, atmospheric, and outer space nuclear tests.  More than 100 countries have ratified the treaty since 1963.


December: The Atomic Energy Commission ceases operations at the Weldon Spring Uranium Feed Materials Plant.


July: The Nuclear Nonproliferation Treaty (NPT) is signed.  This treaty called for halting the spread of nuclear weapons capabilities and by 1970, more than 50 countries ratified the NPT.  By 1986, more than 130 countries ratified it.


January: The National Environmental Policy Act (NEPA) of 1969 is signed, requiring the Federal government to review the environmental impact of any action that might significantly affect the environment.

December: The U.S. Environmental Protection Agency is formed.


October: The Energy Reorganization Act of 1974 abolishes the Atomic Energy Commission and creates the Energy Research and Development Administration and the Nuclear Regulatory Commission.


October: The U.S. Department of Energy (DOE) replaces the Energy Research and Development Administration and consolidates Federal energy programs and activities.


November: The Uranium Mill Tailings Radiation Control Act of 1978 directs DOE to stabilize and control uranium mill tailings at inactive milling sites and vicinity properties.  DOE forms the Uranium Mill Tailings Remedial Action (UMTRA) Program as a result.


March: The Three Mile Island nuclear power plant near Harrisburg, Pennsylvania suffers a partial core meltdown.  Minimal radioactive material is released.

June: The United States and Soviet Union sign the Strategic Arms Limitation Treaty (SALT) II which limits each side's arsenals and restricts weapons development and modernization.


December: The Comprehensive Environmental Response, Compensation and Liability Act (also known as Superfund) is passed in response to the discovery in the late 1970's of a large number of abandoned, leaking hazardous waste dumps.  Under Superfund, the Environmental Protection Agency identifies hazardous sites, takes appropriate action, and sees that the responsible party pays for the clean-up.


January: The Nuclear Waste Policy Act of 1982 is signed, authorizing the development of a high-level nuclear waste repository.


January: Soviet President Gorbachev calls for disarmament by the year 2000.

April: The Chernobyl Nuclear Reactor meltdown and fire occur in the Soviet Union.  Massive quantities of radioactive material are released.

October: The DOE takes custody of the former Weldon Spring Uranium Feed Materials Plant and site characterization begins.  The environmental remediation program is conducted under the CERCLA law and is known as the Weldon Spring Site Remedial Action Project.


December: The Nuclear Waste Policy Amendments Act designates Yucca Mountain, Nevada, for scientific investigation as a candidate site for the nation's first geological repository for high-level radioactive waste and spent nuclear fuel.


November: DOE changes its focus from nuclear materials production to one of environmental clean-up, openness to public input and overall accountability by forming the Office of Environmental Restoration and Waste Management.

The Berlin Wall is torn down.  Many communist governments in Eastern Europe collapse.


October: Congress passes the Radiation Exposure Compensation Act (RECA).  This act provides payments to individuals who contracted certain cancers and other serious diseases as a result of their exposure to radiation released during above-ground nuclear weapons tests ('downwinders') or as a result of their exposure to radiation during employment in underground uranium mines.

November: The Conference on Security and Cooperation in Europe formally ends the Cold War and reduces Warsaw Pact and NATO conventional forces.


May: 178 nations renew the Nuclear Non-Proliferation Treaty.


July: The DOE and Secretary of Energy Bill Richardson acknowledge that nuclear weapons workers placed in harms way should be compensated for suffering occupational illnesses as a result of exposure to the unique hazards in building the Nation's nuclear defense.


July: RECA Amendments pass and added two new claimant categories (uranium mill workers and ore transporters), provided additional compensable illnesses, lowered the radiation exposure threshold for uranium miners, included above-ground uranium miners, modified medical documentation requirements, and removed certain lifestyle restrictions.  It also added additional geographic areas to the downwinder claimant category.

October: The Energy Employees Occupational Illness Compensation Program Act (EEOICPA) passes.  This act provides a $150,000 lump sum payment and related medical expenses to workers who contracted certain diseases as a result of exposure to beryllium, silica or radiation while working for the DOE, its contractors or subcontractors in the nuclear weapons industry.  Under the EEOICPA, benefits are also paid to qualified survivors of deceased employees and uranium employees previously compensated under the RECA.


July: The EEOICPA becomes effective on July 31.

August: Yucca Mountain in Nevada is initially approved to become a storage facility for high level nuclear wastes.


The Defense Authorization bill amends the EEOICPA adding Department of Labor administration of portions of the program and providing additional benefits for RECA and EEOICPA claimants.


February: Special Exposure Cohort status is given to Mallinckrodt Destrehan Street workers (1942-1948).  This status allows eligible employees with any of 22 specified cancers to be compensated without determination of radiation dose and causation.




The Process

1.  Sampling Plant:  Raw Materials Preparation
Mallinckrodt Chemical Works was an official payment-sampler for the Atomic Energy Commission (AEC).  Uranium ore concentrates known as 'yellowcake' were shipped from various mills in the United States and the samples were analyzed for uranium content.  The AEC would pay the mills on the basis of the analytical results.  For example, a single lot of uranium ore concentrate might contain as much as 25,000 pounds of uranium, worth nearly $250,000 at the time.  The sample for analysis might weigh as little as 1/1000 of a pound.  Thus, the goal of the sampling plant was to take the most accurate, representative sample possible to determine uranium content.

2.  Refinery:  Production of Uranium Trioxide
Uranium trioxide, also known as orange oxide, was produced in three steps: digestion, purification by solvent extraction, and denitration.

Digestion:  Ore concentrates received from the Sampling Plant were added to nitric acid and heated.  The resulting slurry contained uranyl nitrate, small amounts of nitric acid, and various impurities.

Solvent Extraction:  The slurry was mixed with tributyl phosphate (TBP) in hexane.  After the mixing phase, the TBP would contain uranyl nitrate and small amounts of impurities.  A byproduct called raffinate contained most of the impurities.  Raffinate was separated out and stored in open pits.  Uranyl nitrate was then extracted from the TBP-hexane solvent.

Denitration:  The purified uranyl nitrate solution was evaporated and pumped to gas-fired denitration pots to produce pure uranium trioxide.

3. Green Salt Plant:  Production of Uranium Tetrafluoride
Reduction and hydrofluorination produced uranium tetrafluoride, also known as green salt.

Reduction:  Uranium trioxide was converted to uranium dioxide by a process known as a two-stage fluid bed reduction reactor.  Some uranium dioxide was utilized in the creation of fuel elements for nuclear power plants, but most was converted to green salt.

Hydrofluorination:  The hydrofluorination reactors were developed by Mallinckrodt Chemical Works and consisted of a series of three horizontal cylinders with motor-driven spiral screws.  Uranium dioxide would be pushed through each cylinder and reacted with hydrogen fluoride gas.  Temperatures within each cylinder were controlled from about 450 to 1,100 degrees F.  Green salt resulted from this process.  Green salt was either used in the Metal Plant or shipped to other AEC installations.

4. Metal Plant:  The Production of UraniumReducing uranium tetrafluoride (green salt) with magnesium made uranium metal.  The reaction took place in a large steel canister called a 'bomb'.  The bomb was first lined with magnesium fluoride in order to protect it from the intense heat that was generated during the reaction.  Green salt was mixed with magnesium chips and then packed in the bomb.  A furnace heated the mixture to start the chemical reaction, which would then proceed spontaneously.  After cooling for about three days, the uranium metal 'dingot' (short for direct ingot) was removed from the bomb and the magnesium fluoride chipped away.  After machining to remove surface impurities, about 3,000 pounds of pure uranium metal measuring about 17 inches in length by 17.5 inches in diameter was the result.  Machined dingots were extruded into rods 13 feet long and 7 inches in diameter for use by other AEC installations.



It All Began in. . . From the Mallinckrodt Chemical Works Tour Guide Book for the
Weldon Spring Uranium Feed Materials Plant dated January 1959

April 1942.  Big things were being done quietly in those days.  Shrouded in secrecy, the greatest brain trust in history had undertaken to release the enormous energy of the atom for the defense of the free world.

Under the trees on the campus of the University of Chicago, three men sat quietly talking.  One, an eminent physicist and Nobel prize-winner, was a leader of a group of scientists determined to marshal the nation’s highest technical facilities for this purpose.  His name:  Arthur Holly Compton.  He told his companions, just in from St. Louis, that he and his colleagues face a problem of vital importance to the war effort.  The crucial requirement was for pure uranium oxide, far purer than it had ever before been prepared except in test tubes. Moreover, his people would need tons of it, first for experimentation, later for its ultimate use.

The visitors from St. Louis, Henry V. Farr and John R. Ruhoff, were chemists from Mallinckrodt Chemical Works, a firm with a long-established reputation for more than ordinary skill in the manufacture of fine chemicals.  Edward Mallinckrodt had asked his technical managers to give his friend Compton whatever he wanted, if humanly possible. 

Compton explained that an ether extraction process had been developed for the purification of uranium nitrate, which worked on a laboratory scale.  Could Mallinckrodt, with long experience in handling ether, adapt it for use in tonnage production of uranium oxide, and achieve the necessary high purity?  The specifications were rigid.  Extreme purity was required.  Time was short; but the assignment did not differ greatly from many others undertaken by Mallinckrodt chemists, also on a highly confidential basis, for the chemical and pharmaceutical industries.

Back in St. Louis, these men quietly, secretly put Mallinckrodt’s technical organization to work.  Less than 15 weeks later the primary problems of commercial production had been solved, a new plant had been designed, built, put into operation, and Dr. Comptons’ scientists were getting uranium oxide. 

After it was all over, the Smyth report recorded:  “Delivery started in July 1942 at a rate of 30 tons a month…it was a remarkable achievement to have developed and put into production on a scale of the order of one ton per day a process transforming grossly impure commercial oxide to oxide of a degree of purity seldom achieved even on a laboratory scale.”

By the fall of 1942, the need was for uranium metal and lots of it.  The Manhattan Project had been created and a chain of supply had been set up in the country, starting with normally available uranium  products and going on, through the oxide step, all the way to metal.  DuPont, Harshaw, Electromet, Linde, Iowa State College and many other organizations had been working on various phases of uranium production.  But still more output was needed.  Some of these companies built new plants for oxide production.  Mallinckrodt’s operations were expanded to include uranium metal production.  Technical information was freely exchanged among these cooperative groups, with the result that their combined production supplied the uranium needed for the atomic energy program.

V-J Day left us with a miraculous achievement, a great and threatening secret – and hope for a bright new future with atomic energy as a peacetime ally.  But the job was still unfinished.  To ensure an adequate supply of uranium, the United States must be able to process any uranium-containing raw material – domestic or imported, crude or refined – in the amounts needed.  This meant the development of new processes, the designing of new plants.  A challenging engineering problem loomed on the horizon. 

With the war over, production of uranium metal was centralized, and it fell to Mallinckrodt to apply the accumulated experience, that of others as well as their own, to the development and integration of processes for producing pure metal from ores.  Leading engineering and construction firms were called in.  In cooperation with Mallinckrodt chemists and engineers, and under the sponsorship first of the Army, later of the Atomic Energy Commission, new facilities were designed and built – facilities that have been the prototypes for others subsequently built.

This is an important part of America’s atomic energy story, and the story of a Mallinckrodt assignment.

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Last Updated: 6/4/2015