Tour the Secret City of Oak Ridge

VIsit the First Nuclear Reactor; See Where Atomic Bomb Fuel Was Made

Jul 23, 2007

Hop on a bus at Tennessee's American Museum of Science and Energy and travel back to WW II, to the Cold War, and on to today's world-class sub-atomic research facilities.

The two-and-a-half-hour guided tour spans over 60 years of scientific history at Oak Ridge National Laboratory, covering:

Built in the isolated Bear Creek Valley during World War II, Y-12 grew to hold thousands of workers, many of them women. The workers were brought in from all over the nation to operate calutron machines designed to separate the two main isotopes of uranium--U-235 and U-238. In nature, the amount of U-235 is less than 1%. To create the fuel that would explode a bomb, the naturally radioactive U-235 had to be enriched to over 90%.

The calutron, invented by Lawrence O. Berkley, was based on the mass-spectrometer, a machine that separates nearly identical isotopes based on their different atomic weights. The calutrons shot ionized uranium gas through a huge magnet, which bent the stream of atoms. The difference in atomic weight caused the paths of the two isotopes in the gas to separate slightly, making it possible to capture tiny amounts of U-235.

Over 1,500 calutron machines at the Y-12 plant enriched most of the uranium used in the "Little Boy" bomb, the first atomic bomb dropped on Japan. The calutron process turned out to be less efficient than the later gaseous diffusion process (see K-25 below), and most of the calutrons were dismantled by 1947.

After WW II, some Y-12 scientists applied their knowledge of radioactivity to detect and treat diseases such as cancer. Y-12 continues to play an important role in storing and recycling weapons-grade uranium, and developing cleanup methods for radioactive contamination. It also serves as a center for homeland security research.

Second stop: X-10 and the Graphite Reactor.

Across a ridge and into the Bethel Valley, are the X-10 plant and the Graphite Reactor, which became the world's first continuously operated reactor. It was built in less than a year, in the rush for atomic weapons to win the war.

Here, scientists proved that they could create enough plutonium 239--a radioactive element made from uranium--to detonate a second type of weapon. The result was the "Fat Man" bomb, detonated over Nagasaki, Japan, and ending the war.

The Graphite Reactor, designated a National Historic Landmark, is open to the public. The tour takes you inside the original reactor building, and past a life-size diorama of workers shoving uranium target rods through the seven-foot-thick concrete walls into the core. Before leaving the building, you can climb the stairs to sit at the actual control panel with the original instrumentation in place when the reactor first went critical on November 4, 1943.

Continuing on through the X-10 plant by bus, you glimpse the High-Flux Isotope research reactor, the "Mouse House," where biologists study radioactive effects on mouse and human genetics, and many other research buildings.

Third Stop: The K-25 Gaseous Diffusion Plant

Driving to yet another protected valley, the bus arrives at an overlook of the huge K-25 plant, where a "gaseous diffusion" process for enriching the amount of U-235 in uranium was used. The K-25 building is half a mile long and larger than the Pentagon (It was built by the same man, Leslie R. Groves, the Army General in charge of building the three secret sites of the Manhattan Project.).

Gaseous diffusion makes use of the slight difference in mass of U-235 and U-238 isotopes. A long series of porous membranes, arranged in a "cascade," gradually reduced the concentration of U-238 and increased the concentration of U-235. The K-25 plant continued its uranium enrichment operation, for Cold War nuclear weapons development, as well as for nuclear power plant fuel, until the 1970s.

Atop Chestnut Ridge between X-10 and Y-12, sits a brand-new, world-class research facility run by a consortium of six DOE research labs. The term "spallation" comes from a German word that describes what happens when you hit a rock with a hammer--scattering bits in all directions.

At the SNS, proton beams are accelerated to almost the speed of light towards a target full of the element mercury. When the protons crash into the mercury nuclei, highly energized neutrons scatter away.

Scientists from all over the world are expected to use these high-powered, pulsed neutron beams to study materials at the atomic level. Discoveries made with neutron beam research at other facilities have already provided us with many of the objects we use every day: pocket calculators, compact discs, and medical imaging equipment, for example. Researchers expect the SNS to bring even more advanced materials for a wide range of applications, such as fiber optics, airplanes and semiconductors used in consumer electronics.

Not to be Missed: D. Ray Smith, official Y-12 historian, telling the story of train loads of uranium ore arriving daily in Oak Ridge, but nothing except "salesmen," handcuffed to locked briefcases (containing minute amounts of enriched uranium and plutonium) leaving town.

Tour Information: June through September, Monday through Friday at 12 noon. For U.S. Citizens only, ages 10 and up. Sign up the morning of the tour at the American Museum of Science and Energy, 300 S. Tulane Avenue, Oak Ridge, TN 37830, (865) 576-3200.

The copyright of the article Tour the Secret City of Oak Ridge in Physics History is owned by Holly Martin. Permission to republish Tour the Secret City of Oak Ridge in print or online must be granted by the author in writing.