1952 – Chalk River, Ontario, Canada, NRX Reactor Melted Down

/ AGR Daily News

12 December 1952 – Chalk River, Ontario, Canada – Reactor core melted down
A reactor shutoff rod failure, combined with several operator errors, led to a major power excursion of more than double the reactor’s rated output at AECL‘s NRX reactor. The operators purged the reactor’s heavy water moderator, and the reaction stopped in under 30 seconds. A cover gas system failure led to hydrogen explosions, which severely damaged the reactor core. The fission products from approximately 30 kg (66 lb) of uranium were released through the reactor stack. Contaminated light-water coolant leaked from the damaged coolant circuit into the reactor building; some 4,000 m3(140,000 cu ft) were pumped via pipeline to a disposal area to avoid contamination of the Ottawa River. After the incident, approximately 1202 people were involved in the two year cleanup.[1] No immediate fatalities or injuries resulted from the incident; a 1982 follow-up study of exposed workers showed no long-term health effects, though Atomic Energy of Canada Limited (AECL) dosimetry files were lost in a 1956 fire . Future U.S. President Jimmy Carter, an engineer and then a Lieutenant in the US Navy, was among the cleanup crew.[2] http://en.wikipedia.org/wiki/List_of_civilian_nuclear_accidents

According to Wikipedia; “NRX was a heavy water moderated, light water cooled, nuclear research reactor at the Canadian Chalk River Laboratories, which came into operation in 1947 at a design power rating of 10 MW (thermal), increasing to 42 MW by 1954. At the time of its construction it was Canada’s most expensive science facility and the world’s most powerful nuclear research reactor.[1] Although nuclear reactors would not generate electricity until 1951,[2] NRX was remarkable both in terms of its heat output and the number of neutrons it generated.

When a nuclear reactor is operating its nuclear chain reaction generates many billions of free neutrons, and in the late 1940s NRX was the most intense neutron source in the world. 

NRX experienced one of the world’s first major reactor accidents on 12 December 1952. The reactor began operation on 22 July 1947 under the National Research Council of Canada, and was taken over by Atomic Energy of Canada Limited (AECL) shortly before the 1952 accident. The accident was cleaned up and the reactor restarted within two years. NRX operated for 45 years, being shut down permanently on 8 April 1993.[3] It is currently undergoing decommissioning at the Chalk River Laboratories site.”
http://en.wikipedia.org/wiki/NRX

Wiki seems to downplay any and all nuclear accidents that it does mention. Here is a much more informative quote from a much longer article about this nuclear disaster, hidden in plain sight; 
“”The NRX reactor underwent a violent power excursion that destroyed the core of the reactor, causing some fuel melting. Unaccountably, the shut-off rods failed to fully descend into the core. A series of hydrogen gas explosions (or steam explosions) hurled the four-ton gasholder dome four feet through the air where it jammed in the superstructure. Thousands of curies of fission products were released into the atmosphere, and a million gallons of radioactively contaminated water had to be pumped out of the basement and ‘disposed of’ in shallow trenches not far from the Ottawa River. The core of the NRX reactor could not be decontaminated; it had to be buried as radioactive waste.” (Dr. Gordon Edwards, CCNR)” Many more details on this nuclear disaster at; 

End

1952 – NRX Reactor Melted Down in Ontario, Canada; via @AGreenRoad
http://agreenroad.blogspot.com/2014/04/1952-nrx-reactor-melted-down-in-ontario.html


For a more complete list of all nuclear plant meltdowns globally, go to;

Nuclear Accidents, Recycling Nuclear Weapons/Fuel
http://agreenroad.blogspot.com/p/nuclear-accidents-around-world.html