The 94 MWe prototype fast breeder reactor Fermi 1 unit under construction and development at the site from 1957 to 1972. On October 5, 1966 Fermi 1 suffered a partial fuel meltdown. According to the United States Nuclear Regulatory Commission, there was no abnormal radiation release to the environment.
The main cause of the temperature increase was a blockage in one of the spigots that allowed the flow of cooled liquid sodium into the reactor. The blockage caused an insufficient amount of coolant to enter; this was not noticed by the operators until the core temperature alarms sounded. Several fuel rod subassemblies reached high temperatures of around 700 °F (370 °C) (with an expected range near 580 °F, 304 °C), causing them to melt.
Following an extended shutdown that involved fuel replacement, repairs to vessel, and cleanup, Fermi 1 continued to operate intermittently until September 22, 1972, but was never again able to reach a fully operational state. It was officially decommissioned December 31, 1975. It is currently in SAFSTOR with a gradual "final" decommissioning in progress.
A number of accounts of the accident are available. There is some debate about whether the details of the accident as written in the book Fermi-1 New Age for Nuclear Power and published by the American Nuclear Society in 1979 are completely accurate. Several of the claims in the ANS's account are contradicted by certain parts of We Almost Lost Detroit, a book written by local Detroit newsman John Grant Fuller (subtitled "This Is Not A Novel"). The book Normal Accidents, written by Yale professor Charles Perrow, describes this accident in more details.
Read more about this topic: Enrico Fermi Nuclear Generating Station