While the U.S. Manhattan project refined and enriched uranium for an atomic bomb in the early 1940, a parallel project was carried out to create plutonium. Plutonium is very rare in nature so it was necessary to create nuclear reactor in which plutonium could be generated by injecting neutrons into a mass of uranium. Most naturally occurring uranium is the U-238 isotope. When U-238 is bombarded with neutrons, some of it is converted to U-239 by absorption of a neutron. The U-239 immediately decays into neptunium-239 by a neutron emitting an electron which leaves behind a new proton. This process occurs again to create plutonium-239. A very small amount of plutonium results from this process and it must be chemically separated from the unconverted uranium and purified.
In March of 1943, the air cooled X-10 Graphite Reactor was built at the Oak Ridge facility in Tennessee. It consisted of a huge block of graphite that measured twenty four feet on each side. That cube was encased in seven feet of dense concrete as a radiation shield. There were initial problems with finding a way to encase the uranium slugs with a sealed metal shell to prevent corrosion and release of fission products. Several different approaches were tried and ultimately aluminum cans were welded with new techniques were developed. About thirty six tons of uranium were fed into the new reactor and half a gram of plutonium was created within the first month of operation. The reactor continued to produce plutonium for the Manhattan Project for the next year and was retired early in 1945.
While the X-10 was in production, work proceeded at the Hanford facility in Washington on the more advanced water cooled Reactor B that would be water cooled. Six reactors were planned altogether. They were housed in buildings that were one hundred and twenty eight feet high. A total of eight hundred and thirty eight uranium slugs were inserted into Reactor B in mid-September of 1944. In late September, after the reactor had gone critical and fission had begun, the control rods were withdrawn to begin plutonium production. The reactor ran for a while but then the power level dropped and the reactor stopped. It turned out that Xenon-135 being produced during the reactor operation was poisoning the reaction by absorbing neutrons. By loading all two thousand tubes in the reactor, proper functioning was achieved and plutonium could be produced.
Chemists had been working on the problem of how to separate the plutonium from the uranium. Little was known about the chemical properties of plutonium so a lot of basic research was necessary. A process was developed that involved bismuth phosphate that allowed precipitation of plutonium or precipitation of the uranium and impurities from solution. The separation plants consisted of four different buildings which housed a process cell, a concentration building, a purification building and a magazine store. Construction began in April of 1944 at Hanford before final choice of a processing method. New methods of remote control had to be developed to deal with the radioactive materials going through the sequence of buildings. In February of 1945, the first shipment of about two and one half ounces of ninety five percent pure plutonium was sent to the Los Alamos facility in New Mexico.
X-10 Graphite Reactor:
