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Chalk River Nuclear Accident

Chalk River Nuclear Accident

The Chalk River Laboratories or Chalk River Labs and formerly Chalk River Nuclear Laboratories are facilities located near the Chalk River population, Ontario (Canada) dedicated to the investigation of nuclear reactions.

The installation was born in 1942 as a result of the collaboration between British and Canadian nuclear researchers. In 1944 the Chalk River Laboratories were inaugurated and in September 1945 the installation put into operation the first nuclear reactor outside the United States.

The NRX is a research nuclear reactor, moderated by heavy water, cooled by light water. It was built during the war period with the aim of using it for military purposes, although the designers contemplated many other civil applications. At present the Chalk River Laboratories are of great importance in the medical applications of nuclear energy.

The Chalk River facility suffered two nuclear accidents in 1952 and 1958. The first of these would be the first civil nuclear accident in the history of nuclear energy.

First nuclear accident at Chalk River

The first accident occurred on December 12, 1952. The NRX reactor suffered a failure in the shutdown that, together with several bad decisions of the operators of the facilities, caused a chain reaction that more than doubled the power of the nuclear reactor.

Operators opened the 4 pressure containment valves in the cooling system, which caused an explosion that destroyed the core of the nuclear reactor, causing a spill of nuclear fuel.

Inexplicably, the closing of the control rods did not completely fall in the reactor core. A series of explosions of hydrogen gas (or explosions of steam) launched the four-ton dome into the air. Thousands of nuclear fission particles were released into the atmosphere along with one million liters of radioactively contaminated water. The contaminated water had to be pumped out of the basement and poured into shallow ditches, near the Ottawa River.

The core of the NRX reactor could not be decontaminated, but had to be buried as radioactive waste. Instead, a new nuclear reactor, even more powerful, was placed in order to continue its operation.

Jimmy CarterAs a curiosity, a young Jimmy Carter (a nuclear engineer of the US Navy) was one of hundreds of Canadian and American military who were ordered to participate in the NRX cleanup as a result of this nuclear accident. Later  he would be president of the USA.

At that time, the INES Scale (international scale of nuclear events) was not yet created, but at present, due to the characteristics of the accident, it would be at level 5 (accident with risk outside the site).

Second Chalk River nuclear accident

Five years later, in 1958, several metal uranium nuclear fuel rods from the NRU reactor overheated and ruptured inside the reactor core. One of the damaged bars caught fire and broke in two, while it was being removed from the base by a robotic crane. It fell into a shallow maintenance well.

The burning of nuclear fuel was left there, laying deadly nuclear fission products and the emission of alpha particles throughout the Chalk River reactor building. The ventilation system was stuck in the "open" position, which contaminated the access areas of the building, as well as an important area in favor of the wind at the reactor site.

A relay team of scientists and technicians finally extinguished the fire. More than a thousand men were involved in the clean-up operations after these two accidents in Chalk River.

Consequences of the Chalk River nuclear accidents

More than 600 men were needed only for the cleaning of the NRU. The official reports of the AECL (Atomic Energy of Canada Limited) note that very few of these men were exposed to excessive radiation, that is, most of the doses of radioactivity recorded did not exceed the levels that were considered admissible for workers in nuclear facilities at that time. The reports also indicated that there were no adverse health effects caused by the radioactive exposures received.

However, no medical follow-up has been done to see if the population of men involved in Chalk River accidents in the future showed a higher than normal incidence of cancer.

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Last review: August 24, 2015