Manhattan Project & Beyond

Click on a subject to learn more about each step of the Nuclear Process.

There are two basic types of nuclear weapons: fission and fusion. The earliest nuclear weapons were fission, and made from uranium and plutonium.  These were the devices used in WWII.  After WWII, fusion weapons were created to be more efficient, smaller, and lighter.  These weapons are often referred to has hydrogen bombs and consist mainly of deuterium and tritium.

There are two basic types of nuclear weapons: fission and fusion.   Early nuclear weapons were fission devices which utilized uranium (U-235) and plutonium (Pu).  Fission is the splitting of an atom into two or more smaller ones.  The neutrons release and then attack the atoms, resulting in a chain reaction that grows and creates a massive nuclear explosion.  The first fission weapons were designed like a gun.  An explosion drove the U-235 or Pu into a core containing more material and a neutron generator which began the fission reaction.  The gun-like design was not very effective, so an implosion design was created which compressed material using chemical explosives.  Both nuclear weapons used on Hiroshima and Nagasaki were fission devices.

Fusion weapons are the second type of nuclear weapon and are often referred to as thermonuclear weapons, or hydrogen bombs.  Fusion occurs when two or more nuclei are brought together under extreme heat and pressure to form a single heavier nucleus.   Fusion weapons are smaller, lighter, and more efficient than fission weapons.  Fusion weapons are primarily made from deuterium (D, H, or heavy hydrogen) and tritium (T, #H, or hydrogen-3).  While fusion weapons are more effective, they are more difficult to produce because some gases are hard to store safely, some are in short supply, and a high temperature and pressure are required to produce a fusion reaction.

Uranium was a key element in building a nuclear weapon.  Uranium ores were mainly found in mines in Utah, Colorado, New Mexico and Arizona also known as the Four Corners.  Once the uranium was taken from the mines, it would be transported by truck or railroad to a mill where it was refined into “yellowcake.”

At the beginning of the Manhattan Project, most of the world’s available supply of uranium came from Africa, Brazil, Canada, and India.  The main use of uranium was to dye products in the ceramics industry.   Scientists briefed the manager of the largest producing uranium mine in the Belgian Congo, Edgar Sengier, of the potential use of uranium to build a weapon. Due to his fear of a German invasion in Africa, he ordered all of the mine’s stockpile of uranium (1250 tons) to be shipped to the U.S  where it was stored for two years in a warehouse on Staten Island.

In the U.S., uranium was primarily a byproduct of mining for other minerals such as vanadium, which was used to harden steel and had been mined in the western U.S. since 1898. In 1942, with the beginning of the Manhattan Project, an initiative was made to extract any remaining uranium from mines in Wyoming, Utah, Colorado, New Mexico, Arizona, and Texas. By the end of the war, 1350 tons of uranium rich black oxide had been produced.

After the war, uranium was still in high demand to continue the nuclear effort.  In 1950, the “uranium boom” began near Grants, NM when a Navajo sheepherder, Paddy Martinez, was exploring on the Santa Fe railroad property and found some uranium.  In 1952, a geologist, Charlie Steen found uranium just to the south of Moab, UT.  He made over one million dollars from his claim (but unfortunately died bankrupt.)

Once the uranium ores were obtained and transported by truckers or railroad workers to the mills, the ores were refined into a substance called “yellowcake.”  Yellowcake is another name for uranium oxide.  The milling process consisted of crushing the ore, then removing the uranium oxide with acids or alkali solutions.  At one point there were approximately 50 uranium mills in the U.S.  Between the years of 1947-1971, over 85,359,000 tons of uranium ore were processed and 173,973 tons of yellowcake were sold to the Atomic Energy Commission (AEC).

Unfortunately, many illnesses have been attributed to working as a uranium miner, miller, or transporter in the early years of the uranium boom.  Safety precautions used today were not available, and the long term health effects of exposure to uranium and other toxins were unknown.  Many workers contracted lung cancer, pulmonary fibrosis, pneumoconiosis, silicosis, cor pulmonale, and kidney diseases.  The U.S. government established two programs: Radiation Exposure Compensation Act (RECA) and Energy Employees Occupational Illness Compensation Program Act (EEOICPA)) to help compensate workers both financially and medically for those that qualify.

Many refineries, foundries, and fabrication facilities were built across the U.S. to take the raw materials and turn them into usable forms of fuel or materials for the nuclear weapons.

While scientists worked to create a weapon that had never been built, others were working simultaneously to develop processes and devices to refine and fabricate uranium and plutonium in a way to be used as fuel for the weapons.  At the beginning of the Manhattan Project, the largest supply of uranium in the U.S. came from foreign sources.  However, in many of the western states, uranium-rich mine tailings existed from the vanadium mines.  Over 3 million tons of these tailings in Durango, CO and Uravan, CO were shipped to Grand Junction, CO for further refining.

Uranium hexafluoride gas, UF6, is the most useable form of uranium.  Several facilities provided intermediate products (feed materials) like brown oxide and green salt for use in the chain of creating UF6. Some of these facilities included Linde Air Products (NY), Mallinckrodt Chemical Works (MO), and Ames laboratory (IA).

After WWII, more facilities started using the refinery and fabrication processes as the need for nuclear material increased.   Fernald (OH), Weldon Springs (MO), Allied Signal (IL) were significant feed material production facilities.

Nuclear weapons needed uranium that was at least 85% U235, but U235 happens naturally in less than 1% of uranium.  Therefore, two processes were developed to create “enriched” uranium:  use of a special machine called a Calutron, and gaseous diffusion.

Less than 1% of a naturally occurring uranium samples is U235, but this is the isotope needed to produce a nuclear chain reaction when bombarded by neutrons.   Therefore, processes had to be developed to separate the U235 from the most naturally occurring uranium which is isotope U238.  When the separation occurs, the increased U235 is called “enriched” uranium.  Nuclear weapons grade uranium must be at least 85% U235. More resources were spent during the Manhattan Project producing weapons grade uranium than in any other effort.  There are two main methods for producing enriched uranium.

Ernest Lawrence, a scientist at the University of California-Berkley, was asked by the U.S. government to investigate ways to separate the U235 isotope from uranium samples.   Lawrence created a large device called the “Calutron” to collect isotopes after accelerating them through a constant magnetic field.  These Calutrons were then built at the Y-12 facility in Oak Ridge, TN.  At first, they were operated by scientists from California, but soon local women were trained to operate the control panels, which required constant monitoring of meters and dials.  A challenge was accepted by Lawrence that the local operators could operate his Calutrons more efficiently than his experts.  They conducted a test, and the “young hillbilly girls” out-produced the scientists from Berkley!  Eventually, the Y-12 Calutrons produced most of the 90% weapons grade enriched uranium used in the Little Boy fission bomb dropped on Hiroshima.

The second method for producing enriched uranium was by gaseous diffusion.  UF6, or uranium hexafluoride, is diffused through many stages which results in increased U235 particles in each cascaded sample.  The gaseous diffusion actually replaced the Calutrons once the process was perfected.  The three main gaseous diffusion plants were located in Oak Ridge, TN, Portsmouth, OH, and Paducah, KY.

Today, a centrifuge process is the most efficient method to separate uranium into enriched grade uranium.

Plutonium (Pu), Heavy Water, and Lithium were crucial materials in nuclear weapons.

Plutonium (Pu) was another crucial fissile isotope and superior to U235 due to its higher probability of fission.  It produces more neutrons per fission event, takes smaller critical mass to produce the same amount of energy and is cheaper to produce than highly enriched uranium.

The experimental X-10 Graphite Moderated Reactor in Oak Ridge was the first to produce significant amounts of plutonium, but the Hanford facility in Washington was created to produce large amounts of plutonium for the Manhattan Project.  The B reactor built in 1944 was the first large scale nuclear reactor.

Heavy water was used to slow the reaction down in a reactor.  Heavy water contains a neutron moderator because the nucleus has a proton and one or two neutrons.   There was a secret agreement between Canada and the U.S which allowed British Columbia to supply most of the heavy water produced from 1943-1953.  The Savanna River Site (SRS) in South Carolina was built in 1953 to operate heavy water moderated reactors that produced plutonium and tritium.  Against local protest, the government ordered 1500 families to relocate to build SRS and this is how the community of New Ellenton, SC came into existence as it provided housing for displaced families of Ellenton and surrounding areas.

Tritium is a radioactive isotope of hydrogen and must be manufactured, as naturally occurring tritium is very rare.  The nucleus of tritium contains one proton and two neutrons.

Lithium fuses with other elements to form many compounds.  It is a very light metal – in fact, it floats in water.  When lithium is irradiated with neutrons, it produces tritium.

Fabrication was an important step in taking substances and shaping them into useable materials.

While many new substances like uranium and other materials were first being produced, there was no experience in how to fabricate them into useable materials.  In 1942, under the direction of Al Kauffman and John Chipman, the Massachusetts Institute of Technology Metallurgical Project was created.  They developed many innovative processes to fabricate uranium reactor fuel elements and beryllium (Be).

Brush Beryllium (now named Materion) was important in processing and manufacturing beryllium components for early reactors and nuclear weapons.   Unfortunately, Chronic Beryllium Disease (CBD or Berylliosis), is a respiratory condition caused by breathing in beryllium dust and has been identified in many beryllium workers.

Prior to 1950, the processing of uranium into uranium metal was done at over 20 small facilities spread throughout the U.S.  However, between 1951-1989, the Atomic Energy Commission (AEC) consolidated the processing by building two main facilities, the Feed Materials Production Center near Fernald, OH and the Weldon Spring Feed Materials Plant in Weldon Spring, MO.  Both facilities took yellowcake and processed it into orange and brown oxide, then to green salt, and finally into highly purified uranium metal.   Because the majority of facilities worked in secrecy even after WWII, many employees and local residents thought the Feed Materials Production Center produced animal feed, not nuclear materials.

Weapon assembly involves the entire process of putting a nuclear weapon together from beginning to end.

Under the direction of J. Robert Oppenheimer, many of the world’s best nuclear scientists were assembled in Los Alamos, NM in 1943.  In the beginning, there were 200 employees, but it grew to over 8200 employees by the end of the war.  In two years, the workers at Los Alamos successfully built the weapon that was detonated at the Trinity site in New Mexico on July 16, 1945.  Just a few weeks later, the weapons developed were used over Hiroshima and Nagasaki Japan to end WWII.

Besides the materials needed to create a nuclear weapon, there are many other components such as the casing component, delivery system, and fusing system.  The casing component must protect the device, allowing for transportation without detonation, and have aerodynamic and hydrodynamic characteristics.

While Los Alamos National Laboratory was the original site of weapon development and assembly, numerous other sites were created to help with the assembly.  Rocky Flats in Colorado manufactured over 70,000 plutonium triggers in 40 years.   Mound Laboratory in Ohio created neutron generators made from polonium, beryllium, deuterium, and tritium.  The Pinellas Plant in Florida also made neutron generators for 10 years starting in 1957. Lawrence Livermore National Laboratory in California developed processes and equipment for testing thermonuclear weapons.  Sandia Laboratory in California and New Mexico primarily assembled warheads from 1948-1952, but then became part of the design and engineering of weapons safety and security.   Sandia also helped develop the MIRV (Multiple Independently Targetable Reentry Vehicle).  Iowa Army Ammunitions Plant (IAAP) in Iowa started with conventional explosives, but then produced high explosives for nuclear warhead assemblies.  Finally, the Pantex Plant, which is still active today, has assembled or upgraded over 32,000 nuclear weapons and disassembled over 50,000 nuclear weapons.

Testing nuclear weapons in the U.S. occurred from 1945 until 1992.  Testing included above ground, underwater, underground and outer space.  Officially, the U.S. has conducted over 1,054 nuclear tests with the majority taking place at the Nevada Test Site and the Pacific Proving Grounds.


July 16, 1945, 5:30 am, the explosion of the first nuclear weapon, known as “The Gadget” took place at the Trinity Site, White Sands Test Range, New Mexico.   Two nickel plated, gold foil-covered pieces of plutonium were fit together around a small “urchin”, the beryllium and polonium initiator, to form the “pit” assembly.  The weapon was assembled in a wood-framed adobe McDonald farmhouse located two miles from “ground zero.” The pit assembly was inserted into a five foot diameter casing that contained 5,000 pounds of high explosives and uranium tamper metal.  The device was hoisted to the top of a 100 foot tower, where 32 detonators were attached to wires to complete the assembly. The gadget ignited at a temperature 10,000 times hotter than the surface of the sun.  One could see the fireball from 60 miles away.  Windows shattered up to 120 miles away and some saw the flash from as far as 180 miles.  The fireball rose 10,000 feet and the mushroom cloud another 30,000 feet.

The blast created a crater 9 feet deep and 1,100 feet wide into the ground and the test tower was obliterated.  The heat from the explosion melted the desert floor, creating a glassy green substance now called Trinitite. It was estimated it yielded about 22 thousand tons of TNT.

Because this test was seen and felt for miles away, the nearby Alamogordo Air Base was ordered to issue a press release stating a remote ammunition magazine had exploded to avoid questions and suspicion.

Pacific Proving Grounds (1946-1962)

After WWII, the U.S. continued testing nuclear weapons in the Marshall Islands and other islands in the Pacific Ocean.  Over 105 tests, both above ground and under water were conducted.  Even though these tests only amounted to 14% of all U.S. nuclear tests, it comprised 80% (approximately 210 megatons) of the total yield of U.S. weapons testing.   Unfortunately, one of the tests, Castle Bravo in 1954, resulted in fallout spreading over some populated islands.  Many of the natives exposed suffered from cancer and birth defects.  They were testing a new design and scientists underestimated how the materials would react along with a change in the weather, which resulted in the worst nuclear accident for the U.S.

Nevada Test Site (1950-present)

The Nevada Test Site is only 1,350 square miles in size and is located northwest of Las Vegas, NV.  There were 928 nuclear tests done at this site with 100 of them above ground.   The above ground tests were conducted when the prevailing winds were in the northeasterly direction to avoid contamination of Las Vegas and California.  However, fallout downwind did affect other parts of Nevada, Utah, and other western and mid-western states.  In 1963, the U.S. signed the Limited Test Ban treaty which ended above ground testing of nuclear weapons along with underwater or in outer space, but sill permitted underground testing.  Underground tests were conducted at the Nevada Test Site since 1957 and continued until 1992.

Peaceful Uses of Nuclear Weapons

In 1957, the Plowshare Program was established to investigate the peaceful uses of nuclear weapons.  From 1961-1973, 27 tests involving 35 nuclear detonations were conducted in New Mexico, Nevada, and Colorado.  The purpose of the tests was to look at uses such as excavation of canals and harbors, creation of underground cavities for water and waste storage, flood control by creating dams and reservoirs, cap oil or gas leaks, opening rock formations for oil and gas production access, and creating thermal power sources.   Pressure from environmental groups and economic realities resulted in the program being dissolved in 1975.

The threat of nuclear war continues today even with various treaties in place.  While many countries have reduced their production, many, including the U.S. have a large stockpile of nuclear weapons at their disposal if ever needed.

Even with the end of the Cold War and various nuclear treaties in effect, the money spent on nuclear weapons continues today.  The Pantex Plant in Texas recently completed a major expansion to increase its ability to assemble up to 600 nuclear warheads per year.  New tritium reservoirs and uranium reprocessing continues at Y-12 Plant in Tennessee.  Sandia Laboratory has increased its manufacturing of neutron generators to over 1500 per year.  Fourth generation designs are being developed to be processed without special nuclear materials like U235 and Pu.

70,000 warheads have been produced to date in the U.S. Only 32,000 are still in existence, though many are deactivated.  Over 5,000 are currently active and deployable if needed to defend our country.

Though many of the powerful countries of the world have all signed various nuclear treaties, the threat of nuclear warfare continues especially among rogue or radical nations and terrorists.  Iran continues their development of nuclear weapons.  North Korea has developed nuclear weapons and is currently testing missile systems to reach the U.S.  North Korea’s most recent nuclear test occurred in February 2013.  Terrorist cells could gain access to nuclear material, but simply do not contain the ability to produce these at any large scale.