Chalk River Laboratories

Chalk River was also the site of two nuclear accidents in the 1950s. The first incident occurred in 1952, when there was a power excursion and partial loss of coolant in the NRX reactor, which resulted in significant damage to the core. The control rods could not be lowered into the core because of mechanical problems and human errors. Three rods did not reach their destination and were taken out again by accident. The fuel rods were overheated, resulting in a meltdown. The reactor and the reactor building were seriously damaged by hydrogen explosions. The seal of the reactor vessel was blown up four feet. In the cellar of the building, some 4,500 tons of radioactive water was found. This water was dumped in ditches around 1600 meters from the border of the Ottawa River. During this accident some 10,000 curies or 370 TBq of radioactive material was released.[5] Future U.S. president Jimmy Carter, then a U.S. Navy officer in Schenectady, NY, lead a team of 26 men including 13 U.S. Navy volunteers in the hazardous cleanup.[6][7] [8]Arthur V. McKeon and Fred Hieber were among the U.S. Navy volunteers. Two years later the reactor was in use again.[9]

The second accident, in 1958, involved a fuel rupture and fire in the National Research Universal reactor (NRU) reactor building. Some fuel rods were overheated. With a robotic crane, one of the rods with metallic uranium was pulled out of the reactor vessel. When the arm of the crane moved away from the vessel, the uranium caught fire and the rod broke. The largest part of the rod fell down into the containment vessel, still burning. The whole building was contaminated. The valves of the ventilation system were opened, and a large area outside the building was contaminated. The fire was extinguished by scientists and maintenance men in protective clothing running along the hole in the containment vessel with buckets of wet sand, throwing the sand down at the moment they passed the smoking entrance.[10]

Both accidents required a major cleanup effort involving many civilian and military personnel. Follow-up health monitoring of these workers has not revealed any adverse impacts from the two accidents.[11][12] However, the Canadian Coalition for Nuclear Responsibility, an anti-nuclear watchdog group, notes that some cleanup workers who were part of the military contingent assigned to the NRU reactor building unsuccessfully applied for a military disability pension due to health damages.[6]

Chalk River Laboratories remain an AECL facility to this day and are used as both a research (in partnership with the NRC) and production facility (on behalf of AECL) in support of other Canadian electrical utilities.

On November 18, 2007, the NRU, which makes medical radioisotopes, was shut down for routine maintenance. This shutdown was extended when AECL, in consultation with the Canadian Nuclear Safety Commission (CNSC), decided to connect seismically-qualified emergency power supplies (EPS) to two of the reactor's cooling pumps (in addition to the AC and DC backup power systems already in place), which had been required as part of its August 2006 operating licence issued by the CNSC. This resulted in a worldwide shortage of radioisotopes for medical treatments because Chalk River makes the majority of the world's supply of medical radioisotopes, including two-thirds of the world's technetium-99m.[13]

On December 11, 2007, the House of Commons of Canada, acting on independent expert advice, passed emergency legislation authorizing the restarting of the NRU reactor and its operation for 120 days (counter to the decision of the CNSC), which was passed by the Senate and received Royal Assent on December 12. Prime Minister Stephen Harper criticized the CNSC for this shutdown which "jeopardized the health and safety of tens of thousands of Canadians", insisting that there was no risk, contrary to the testimony of then CNSC President & CEO Linda Keen. She would later be fired for ignoring a decision by Parliament to restart the reactor, reflecting its policy that the safety of citizens requiring essential nuclear medicine should be taken into account in assessing the overall safety concerns of the reactor's operation.[14][15][16][17][18] The NRU reactor was restarted on December 16, 2007.

On December 5, 2008, heavy water containing tritium leaked from the NRU.[19] The leaked water was contained within the facility, and the Canadian Nuclear Safety Commission (CNSC) was notified immediately, as required.

In its formal report to the CNSC, filed on December 9, 2008 (when the volume of leakage was determined to meet the requirement for such a report) AECL mentioned that 47 litres of heavy water were released from the reactor, about 10% of which evaporated and the rest contained, but affirmed that the spill was not serious and did not present a threat to public health.[20] The amount that evaporated to the atmosphere is considered to be minor, accounting for less than a thousandth of the regulatory limit.[21] The public was informed of the shutdown at the reactor, but not the details of the leakage since it was not deemed to pose a risk to the public or environment. The leak stopped before the source could be identified, and the reactor was restarted on December 11, 2008 with the approval of the CNSC, after a strategy for dealing with the leak (should it reappear) was put in place.

In an unrelated incident, the same reactor had been leaking 7,001 litres of light water per day from a crack in a weld of the reactor's reflector system. This water has been systematically collected, purified in an on-site Waste Treatment Centre, and eventually released to the Ottawa River in accordance with CNSC, Health Canada, and Ministry of the Environment regulations. Although the leakage is not a concern to the CNSC from a health, safety or environmental perspective,[22] AECL has plans for a repair to reduce the current leakage rate for operational reasons.

In mid-May 2009, the heavy water leak at the base of the NRU reactor vessel, first detected in 2008 (see above), returned at a greater rate and prompted another temporary shutdown that lasted until August 2010. The lengthy shutdown was necessary to first completely defuel the entire reactor, then ascertain the full extent of the corrosion to the vessel, and finally to effect the repairs – all with remote and restricted access from a minimum distance of 8 metres due to the residual radioactive fields in the reactor vessel. The 2009 shutdown occurred at a time when only one of the other four worldwide regular medical isotope sourcing reactors was producing, resulting in a worldwide shortage.