After the catastrophic events at Japan's Fukushima Daiichi nuclear power complex in March 2011, the U.S. Senate conducted a hearing about nuclear plant safety. A senior scientist from the Natural Resources Defense Council (NRDC), Dr. Thomas Cochran, spoke at that event.
Cochran, who taught nuclear physics as the U.S. Naval Academy, explained that 582 commercial nuclear reactors have been built and operated worldwide. Of those, 137 have shut down permanently for various reasons. Twelve have suffered meltdown incidents.
With commercial reactors operating on average just under 26 years each, Cochran calculated that a serious nuclear accident occurs approximately every two years.
What factors affect nuclear plant safety?Cochran said that domestically, the bulk of America’s nuclear fleet relies on 104 aging reactors that have been operating at higher temperatures and for decades longer than originally intended. Risks with those plants do not decrease with age. Based on nuclear energy’s history around the globe, he concluded that “operational reactors worldwide are not sufficiently safe.”
According to Cochran, three primary factors influence nuclear plant safety: the plant’s design, its environmental risks (such as being in an earthquake zone), and the plant’s “culture of safety” (which includes a plant’s official safety guidelines and how closely workers follow them).
During his Senate testimony, Cochran identified twelve nuclear reactors that have had partial or full meltdown incidents. He listed these reactors:
1. Sodium Reactor Experiment (SRE)
Location: Santa Susana Field Laboratory, California
Reactor Type: Sodium-Cooled graphite-moderated thermal power reactor.
Power: 20 Megawatts thermal (MWt); 6.5 Megawatts electric (MWe).
Began Operating: In July 1957, became first nuclear plant to send electricity to the grid.
Melt Down Occurred: Partial core melt accident between July 12 and July 26, 1959, resulting in melting 1/3 of the fuel.
Shut down: Feb. 1964.
2. Stationary Low-Power Reactor #1 ( SL-1)
Location: National Reactor Testing Station (now Idaho National Laboratory)
Reactor Type: Experimental, gas-cooled, water moderated.
Power: 3.3 MWt; 300 KWe.
Began Operating: Initial criticality March, 1960.
Melt Down Occurred: Improper removal of control rods caused steam explosion, ejecting control rods and the upper control mechanism.
Comments: 3 operators killed, including worker who improperly withdrew control rod.
Shut down: May 1964.
3. Enrico Fermi Unit 1
Location: Frenchtown Township, Monroe County, Michigan
Reactor Type: Liquid Metal Fast Breeder Reactor.
Power: 200 MWt; 65 MWe.
Began Operating: August 23, 1966.
Melt Down Occurred: Oct. 5, 1966, two of 105 fuel assemblies melt.
Shut down: Nov. 1972.
4. Chapelcross Unit 2 Nuclear Power Plant
Location: Annan, Dumfreshire, Scotland, UK
Reactor Type: Gas-cooled, graphite moderated; Magnox.
Power: 180 MWt, up-rated to 265 MWt; originally 23 MWe, up-rated to 60 MWe.
Began Operating: Startup May 1959.
Melt Down Occurred: Damage to a single fuel channel May, 1967 resulting in damage to one section of the core.
Shut down: June 2004.
5. Saint-Laurent A-1 Nuclear Power Plant
Location: St. Laurent-Nouan, Loir-et-Cher, Centre, France
Reactor Type: Gas-cooled, graphite moderated.
Power: 1570 MWt; 405 MWe.
Began Operating: Connected to grid March 12, 1969.
Melt Down Occurred: 50 Kg of Uranium melted Oct. 17, 1969.
Shut Down: May 27, 1992.