The Nuclear Plant Outage of Fermi Unit 1

Boomer Fleming
March 7, 2018

Submitted as coursework for PH241, Stanford University, Winter 2018


Fig. 1: Enrico Fermi Atomic Power Plant, Unit 1. (Source: Wikimedia Commons)

Located on the southwest shore of Lake Erie, Michigan, the Enrico Fermi Atomic Power Plant, Unit 1 (seen in Fig.1) is named after famed Italian-American physicist Enrico Fermi. The reactor was a 200 MWt (66 MWe) experiential sodium cooled fast breeder reactor that last operated in 1972. Its realization was led by Walker L. Cisler, former president, CEO, and chair of the board of Detroit Edison. The Power Reactor Development Company was formalized in 1955 and led to construction beginning the year after. In making comparisons at the time with regard to core size and power, Fermi 1 was the largest fast-neutron reactor built to date. Criticality was achieved on August 23, 1963. [1]

Fermi Unit 1 Meltdown

In the first two years of operation, Fermi 1 was kept at power levels below 1 MWt. Over the following 6 months, power levels incrementally increased to 100 MWt. During the increase of power over time, it was noted that coolant temperatures were higher than normal in 2 of the 105 fuel assemblies. [2]

On October 5, 1966 there was a blockage that kept the flow of sodium from reaching part of the core, and caused a partial core meltdown. This was caused by pieces of zirconium that had broken off and blocked sodium flow. Examining the fuel assemblies revealed that melting had occurred in 2 out of the 105. [1] A feature that was introduced late in the reactor's design installed heat-resistant zirconium pieces to shield flow guides from molten fuel, and two had broken loose and caused the meltdown. Inspections that later took place claim that no radioactivity had escaped to the environment and no injuries were reported. [2]

It took about four years to repair damage to the reactor, but a sodium explosion further delayed the reactor's return to generation. In October of 1970, Fermi 1 finally reached a power level of 200 MWt. Only generating 3.4% of its capacity in 1971, PRDC declined to continue to purchase uranium fuel for the plants further operation. After denial of an operating license and shutdown, the plant was officially decommissioned in 1975. [1]


While this outage and ultimate failure of an atomic power plant has largely gone unnoticed in the public eye, it has brought great attention to the problem of flow blockages in sodium coolant by unintended objects. Additionally, Fermi 1 has replicated history in its resulting meltdown regardless of indicating inadequate cooling to its operators on numerous occasions. Because the zirconium objects were actually not an inclusion in the original design of the plant, this event also highlights the necessary avoidance of late additions to the design and construction of reactor systems due to necessary quality control that occurs in the normal design process.

© Boomer Fleming. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] T. B. Cochran et al., "Fast Breeder Reactor Programs: History and Status," International Panel on Fissile Materials, Research Report 8, February 2010, pp. 94-95.

[2] H. W. Bertini et al., "Descriptions of Selected Accidents That Have Occured at Nuclear Reactor Facilities", Oak Ridge National Laboratory, ORNL/NSIC-176, April 1980.