17 February 2009

Breeder reactor

The invention: A plant that generates electricity from nuclear fission while creating new fuel. The person behind the invention: Walter Henry Zinn (1906-2000), the first director of the Argonne National Laboratory Producing Electricity with More Fuel The discovery of nuclear fission involved both the discovery that the nucleus of a uranium atom would split into two lighter elements when struck by a neutron and the observation that additional neutrons, along with a significant amount of energy, were released at the same time. These neutrons might strike other atoms and cause them to fission (split) also. That, in turn, would release more energy and more neutrons, triggering a chain reaction as the process continued to repeat itself, yielding a continuing supply of heat. Besides the possibility that an explosive weapon could be constructed, early speculation about nuclear fission included its use in the generation of electricity. The occurrence of World War II (1939- 1945) meant that the explosive weapon would be developed first. Both the weapons technology and the basic physics for the electrical reactor had their beginnings in Chicago with the world’s first nuclear chain reaction. The first self-sustaining nuclear chain reaction occurred in a laboratory at the University of Chicago on December 2, 1942. It also became apparent at that time that there was more than one way to build a bomb. At this point, two paths were taken: One was to build an atomic bomb with enough fissionable uranium in it to explode when detonated, and another was to generate fissionable plutonium and build a bomb. Energy was released in both methods, but the second method also produced another fissionable substance. The observation that plutonium and energy could be produced together meant that it would be possible to design electric power systems that would produce fissionable plutonium in quantities as large as, or larger than, the amount of fissionable material consumed. This is the breeder concept, the idea that while using up fissionable uranium 235, another fissionable element can be made. The full development of this concept for electric power was delayed until the end of WorldWar II. Electricity from Atomic Energy On August 1, 1946, the Atomic Energy Commission (AEC) was established to control the development and explore the peaceful uses of nuclear energy. The Argonne National Laboratory was assigned the major responsibilities for pioneering breeder reactor technologies.Walter Henry Zinn was the laboratory’s first director. He led a team that planned a modest facility (Experimental Breeder Reactor I, or EBR-I) for testing the validity of the breeding principle. Planning for this had begun in late 1944 and grew as a natural extension of the physics that developed the plutonium atomic bomb. The conceptual design details for a breeder-electric reactor were reasonably complete by late 1945. On March 1, 1949, the AEC announced the selection of a site in Idaho for the National Reactor Station (later to be named the Idaho National Engineering Laboratory, or INEL). Construction at the INEL site in Arco, Idaho, began in October, 1949. Critical mass was reached in August, 1951. (“Critical mass” is the amount and concentration of fissionable material required to produce a self-sustaining chain reaction.) The system was brought to full operating power, 1.1 megawatts of thermal power, on December 19, 1951. The next day, December 20, at 11:00 a.m., steam was directed to a turbine generator. At 1:23 p.m., the generator was connected to the electrical grid at the site, and “electricity flowed from atomic energy,” in the words of Zinn’s console log of that day. Approximately 200 kilowatts of electric power were generated most of the time that the reactor was run. This was enough to satisfy the needs of the EBR-I facilities. The reactor was shut down in 1964 after five years of use primarily as a test facility. It had also produced the first pure plutonium. With the first fuel loading, a conversion ratio of 1.01 was achieved, meaning that more new fuel was generated than was consumed by about 1 percent. When later fuel loadings were made with plutonium, the conversion ratios were more favorable, reaching as high as 1.27. EBR-I was the first reactor to generate its own fuel and the first power reactor to use plutonium for fuel. The use of EBR-I also included pioneering work on fuel recovery and reprocessing. During its five-year lifetime, EBR-I operated with four different fuel loadings, each designed to establish specific benchmarks of breeder technology. This reactor was seen as the first in a series of increasingly large reactors in a program designed to develop breeder technology. The reactor was replaced by EBR-II, which had been proposed in 1953 and was constructed from 1955 to 1964. EBR-II was capable of producing 20 megawatts of electrical power. It was approximately fifty times more powerful than EBR-I but still small compared to light-water commercial reactors of 600 to 1,100 megawatts in use toward the end of the twentieth century. Consequences The potential for peaceful uses of nuclear fission were dramatized with the start-up of EBR-I in 1951: It was the first in the world to produce electricity, while also being the pioneer in a breeder reactor program. The breeder program was not the only reactor program being developed, however, and it eventually gave way to the light-water reactor design for use in the United States. Still, if energy resources fall into short supply, it is likely that the technologies first developed with EBR-I will find new importance. In France and Japan, commercial reactors make use of breeder reactor technology; these reactors require extensive fuel reprocessing. Following the completion of tests with plutonium loading in 1964, EBR-I was shut down and placed in standby status. In 1966, it was declared a national historical landmark under the stewardship of the U.S. Department of the Interior. The facility was opened to the public in June, 1975.

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