October 5, 1966: Partial Meltdown at Fermi 1

Today marks the fortieth anniversary of a partial meltdown at the Enrico Fermi breeder reactor near Detroit, Michigan. On October 5, 1966, a zirconium plate at the bottom of a reactor vessel became loose during a test for full-power. The plate blocked the flow of liquid-sodium coolant, causing two fuel subassemblies to begin to melt. When radiation monitors sounded, operators shut down the reactor manually. The time from the first alarm to partial meltdown was only four minutes. Although the release of Iodine-131 remained confined to the secondary containment system, utility officials briefly considered the possibility of evacuating nearby Detroit.

The Enrico Fermi Atomic Power Plant, Unit 1 (Fermi 1) was designed by Detroit Edison and Dow Chemical, and owned by a consortium called the Power Reactor Development Company. During the 1950s, Argonne National Laboratory had developed the first experimental breeder reactors, EBR-1 and EBR-2, for civilian use. Like these earlier power plants, Fermi 1 was designed to produce or "breed" fuel by producing more fissile material than was consumed. By closing the fuel cycle loop, fast breeder rectors (FBR) could reprocess fuel and achieve the "plutonium economy" that many saw as the future of nuclear power. Unlike EBR-1 and EBR-2, however, Fermi 1 was cooled with liquid sodium and operated at essentially atmospheric pressure.

The world's first liquid-metal fast breeder reactor (LMFBR) was filled with liquid sodium in December 1960. After criticality was achieved, low-power operations began in August 1963. Testing above 1 Mwt commenced in December 1965, shortly after Fermi 1 received a high-power operating license. On October 5, 1966, a zirconium-sodium flow deflector fractured during a full-power test. Overheating damaged two fuel rods and forced operators to shutdown the breeder reactor.

Fermi 1 was restarted in 1970, but shut down again in 1972 when its core approached the burnup limit. According to the Nuclear Regulatory Commission (NRC), the fuel and blanket subassemblies were shipped offsite in 1973. The non-radioactive, secondary sodium system was drained and the radioactive, primary sodium was stored in tanks and drums until removal from the site in 1984.

Resources:

http://www.nrc.gov/info-finder/decommissioning/power-reactor/enrico-fermi-atomic-power-plant-unit-1.html

http://www.ieer.org/reports/accident.html

http://historicmonroe.org/h024.htm

http://www.insc.anl.gov/cgi-bin/sql_interface?view=rx_com_matrix&qvar=unit&qval=546

http://www.nucleartourist.com

http://en.wikipedia.org/wiki/Fast_breeder_reactor