|Fig. 1: President James Earl "Jimmy" Carter over 25 years after his involvement at Chalk River. (Source: Wikimedia Commons)|
On the 12th of December, 1952, a failure occurred in the National Research Experimental (NRX) nuclear reactor at Chalk River Laboratories in Ontario, Canada. The accident occurred when an error was made in in calculating the amount of heavy water required to cool the reactor, which caused the reactor power to rise.  The safety mechanism in place to halt this process, which would have impeded the chain reaction by lowering rods of neutron-absorbing material into the reactor, failed. [1,2] Resultingly, the reactor power continued to rise until an operator in the control room triggered a system that disposed of the heavy water from the reactor into its holding tank. This effectively shut down the reactor, but the uranium element had already become molten and destroyed the cooling compartment in which it was situated.  A substantial amount of gaseous radioactive matter was released through the ventilation system high over the site, triggering all of the radiation alarms in the plant. Accordingly, the entire plant was evacuated. Among the men involved in the restoration of the reactor was future President of the United States, Jimmy Carter (Fig. 1); who, despite his experience at the site and later presiding over Three Mile Island, continued to support the potential for safe and effective nuclear energy. 
In order to repair the reactor at Chalk River Laboratories (Fig. 2), a wide array of experts were assembled to clean the any spilled radioactive material, replace the damaged reactor components, remove the damaged fuel elements, and improve the controls and shielding mechanisms in the lab.  This coalition included the Atomic Energy of Canada Limited (AECL), the Canadian Army, the Royal Canadian Air Force, and the U.S. Navy were involved.  A young Lieutenant Carter of the U.S. Navy was involved in the mission to remove the radioactive reactor from the site. The intensity of the radiation meant that each person involved in this effort could only spend about ninety seconds at the hot core location based on estimations of acceptable levels of radiation exposure.  In order to for the team to gain knowledge of the reactor design that would allow them to effectively utilize their limited window. A replica of the reactor was constructed on a nearby tennis court and cameras in the below-ground chamber monitored the damaged reactor and each time a team member managed to remove an element from the core, the equivalent piece was removed on the mock-up.  Eventually, Carter, among others in the group, descended into the reactor and worked frantically to remove the damaged fuel rods. After the rods were removed it was clear that the moderator tank was irrecoverable, so the tank was lifted out by an overhead crane and then buried in a canvas bag over a mile away at a waste management site.  The entirety of the operation took just fourteen months. 
|Fig. 2: Chalk River Laboratories in 2008. (Source: Wikimedia Commons)|
Occurring in the infancy of industrial nuclear power, this accident and subsequent recovery mission had profound effects on the understanding of safety mechanisms in nuclear reactors. The NRX reactor at the time was outfitted with emergency water cooling that would be activated if the regular cooling were to fail and would remove the afterheat from the fission products even once the chain reaction had ceased.  This emergency water cooling would not only cool the reactor but also recover and dispose of fission byproducts that could have leaked into the containment vessel. This system was supplemental to the neutron-absorbing shut-off rods intended to halt the chain reaction when lowered into the reactor (that failed on the day of the incident).  Nonetheless, these safety systems were not infallible and the containment vessel surrounding the reactor was meant to be the last-ditch safety system that would prevent the release of any radioactivity. However, in the wake of the incident the Atomic Energy Commission (AEC) commissioned the Brookhaven National Laboratory in 1957 to estimate the consequences of a failure in such a reactor. Brookhaven obtained dramatic results, estimating 3,400 casualties from the radiation and property damage of $7 billion.  Despite these findings, the AEC did not release the report on the basis that no explanation was provided for how such a failure would occur or its likelihood. But, it was soon recognized that large scale reactors in development were capable of melting through their containment vessels if they were to lose access to cooling. This realization brought to light the very real possibility of catastrophic failure in the event that the cooling system should fail, and led to the prioritization of failsafe and redundant cooling mechanisms to ensure that the reactor would always be cooled to avoid a breach of the containment vessel. 
© Zachary Meza. 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.
 K. Krenz, Deep Waters: The Ottawa River and Canada's Nuclear Adventure (McGill-Queen's University Press, 2004), p. 95.
 A. M. Weinberg, The First Nuclear Era: The Life and Times of a Technological Fixer (American Institute of Physics, 1994), p. 194
 J. Carter, A Full Life: Reflections at Ninety (Simon & Schuster, 2015).
 J. Carter, Why Not the Best?: the First 50 Years (University of Arkansas Press, 1996), p. 54.