REACTOR OPERATIONS

• Fuel and Target Fabrication
• Reactor Operations
• Chemical Separation
• Met Lab and Oak Ridge Hazards and Wastes
• Hanford Hazards and Wastes

Not existing naturally in any significant quantities, plutonium had to be made. Making plutonium involved the fission of uranium-235 to produce neutrons that would then be absorbed by atoms of uranium-238 to form the short lived uranium-239. In uranium-239 (an atom with 92 protons and 147 neutrons), a neutron would undergo beta decay to produce a proton, leaving an atom of neptunium-239 (with 93 protons and 146 neutrons), which in turn beta decayed into plutonium-239 (with 94 protons and 145 neutrons). The plutonium studied by scientists such as Glenn Seaborg was created in the laboratory in small amounts, using a cyclotron. The bomb project, however, needed much larger quantities of plutonium and required a substantially different approach to plutonium production. The industrial—scale production of plutonium involved nuclear reactors, or piles.

The first reactor CP-1 (Chicago Pile-1), later relocated and rebuilt as CP-2, was designed and built by the Metallurgical Laboratory (often called the "Met Lab") at the University of Chicago. This experimental reactor was used by Enrico Fermi and his team to investigate the basic physics of chain reactions and uranium. CP-1 was essentially an assembly of natural uranium within a 385-ton structure of graphite bricks. Since only six tons of uranium metal were available, Fermi had to use an additional 34 tons of uranium oxide to complete the reactor. The reactor assembly was initially intended to be spherical in shape. Critical conditions were achieved somewhat sooner than anticipated, however, and the assembly took the shape of a sphere flattened at the top. Cadmium strips, which could be removed and inserted into the assembly, were used to control the chain reaction. The reactor was operated at a power level of only half a watt, with brief intervals at 200 watts.

CP-1, important as it was, provided little technical guidance when it came to the complicated cooling, control, and shielding systems required of a large reactor. Met Lab and the DuPont Corporation, which would build and operate the Hanford reactors, decided first to construct an experimental, air-cooled production reactor at the Oak Ridge X-10 site that would aid in the design, construction, and operation of the then planned helium-cooled production reactors at Hanford. Much more a piece of highly engineered industrial equipment than the science experiment that CP-1 was, the X-10 reactor consisted of a huge block of graphite, measuring 24 feet on each side, surrounded by several feet of high-density concrete that served as a radiation shield. The block was pierced by 1,248 horizontal, diamond-shaped channels in which rows of cylindrical uranium slugs formed long rods. Cooling air circulated through the channels on all sides of the slugs. After a period of operation, operators pushed fresh slugs into the channels from the face of the pile, and the irradiated slugs would fall from the back wall through a chute into an underwater bucket. Designed to operate at a power level of 1,000 kilowatts, the X-10 reactor supplied the Los Alamos lab with the first significant amounts of plutonium, as well as provided invaluable experience for engineers, technicians, reactor operators, and safety officials who then moved on to Hanford.

DuPont chose a slightly different design, using water as a coolant, for the three production reactors at Hanford. Similar to the X-10 reactor in terms of loading and unloading fuel, the Hanford reactors were built on a much larger scale. Whereas the X-10 had an initial design output of 1,000 kilowatts, the Hanford reactors were designed to operate at 250,000 kilowatts. Consisting of a 28- by 36-foot, 1,200-ton graphite cylinder lying on its side, each Hanford reactor was penetrated through its entire length horizontally by 2,004 aluminum tubes. Two hundred tons of uranium slugs, the size of rolls of quarters and sealed in aluminum cans, went into the tubes. Cooling water from the Columbia River, which first had to be treated, was pumped through the aluminum tubes around the uranium slugs at the rate of 30,000 gallons per minute. Water consumption approached that of a city of a third of a million people. Each reactor had its own auxiliary facilities that included a river pump house, large storage and settling basins, a filtration plant, huge motor-driven pumps for delivering water to the face of the pile, and facilities for emergency cooling in case of a power failure.

The first full-scale production plant, the B-Reactor at Hanford, began operations on September 13, 1944, though it quickly exhibited a feature unexpected by the physicists. The scientists continued to increase the power in the reactor over the next several days, until the power suddenly fell on the 28th, eventually shutting the reactor down altogether. The physicists determined that this effect was due to another fission product, xenon-135, which absorbed neutrons and ended the chain reaction. After waiting a few days for the xenon to decay, reactor operations resumed. Ultimately, scientists circumvented the problem of xenon poisoning by increasing the power of the reactor enough to overwhelm the xenon. As reactor operations became routine, the canned uranium slugs periodically would be discharged in quantities of several tons and sent to Hanford's 200 area for plutonium separation.

• Fuel and Target Fabrication
• Reactor Operations
• Chemical Separation
• Met Lab and Oak Ridge Hazards and Wastes
• Hanford Hazards and Wastes

Previous      Next