Tennessee
120
X-10 Graphite Reactor, Oak Ridge, TN
35° 55′ 34.85″ N, 84° 18′ 59.27″ W
The World’s First Viable Nuclear Reactor
The Oak Ridge National Laboratory was created in 1943, at the same time the town of Oak Ridge, Tennessee, was built to house the laboratory’s workers and their families. The laboratory was originally created as part of the Manhattan Project to build the first nuclear bomb, and its role was the production of the uranium and plutonium needed for the bomb.
To produce the plutonium (see page 376), the laboratory first needed to extract the fissile Uranium-235 isotope and then place it in a nuclear reactor. So not only did the uranium extraction plant have to be created, but the first significant nuclear reactor as well.
The only working nuclear reactor in 1943 was a small proof-of-concept, created by Enrico Fermi (see Chapter 97) and known as the Chicago Pile (it had been built under Stagg Field stadium in Chicago). But the Chicago Pile was much too small for real use, and so the X-10 Graphite Reactor was built at Oak Ridge. It operated from 1943 to 1963 and is now open to the public.
The reactor consists of a cube of graphite with edges over 7 meters long and encased in concrete 2 meters thick. Cut into the graphite are 1,248 diamond-shaped slots, into which aluminum cylinders containing a mixture of Uranium-235 and Uranium-238 were inserted. The entire reactor could contain almost 50 tonnes of fuel. The fuel cylinders were inserted by hand (Figure 120-1) from the east side of the reactor; when they were used up, they were pushed through to the western side using long rods and fell out into a deep pool of water. There they lay until the radiation had died down and they could be collected for further processing.
Since the Uranium-235 is fissile, it decays to give off neutrons that go on to hit other Uranium-235 atoms and split them apart, leading to a chain reaction (see page 376). In the X-10 reactor, the fast neutrons from the reaction are slowed by the graphite blocks to become “thermal neutrons”; these have the right energy level to be absorbed by Uranium-235 to keep the reaction going.
Figure 120-1. Inserting the fuel cylinders
To control the speed of the reaction, the reactor had vertically mounted rods made of boron and steel. The rods could be inserted into holes in the reactor to slow (or even stop) the chain reaction. Another set of boron-and-steel rods passed through the reactor horizontally to control the reaction. The boron absorbed the neutrons, preventing (or slowing down) the chain reaction.
The X-10 reactor was the test bed for many nuclear technologies and proved the viability of nuclear reactors. In addition to producing plutonium for the first atomic bombs, it was later used to create radioisotopes for medical use.
Visitors can view the reactor control room and the east side (where fuel was loaded) on a guided tour of the laboratory. Tours start at the American Museum of Science and Energy, which tells the story of the Oak Ridge National Laboratory and the Manhattan Project. The museum also presents nuclear power in the wider context of energy production.
Practical Information
The American Museum of Science and Energy is open to all; its website is at http://www.amse.org/. Tours of the Oak Ridge National Laboratory start at the museum and are held daily; however, due to the sensitive nature of the laboratory’s work, tours are only open to U.S. citizens with advance bookings and identification. Details are available from http://www.ornl.gov/ornlhome/visiting.shtml.
