On August 1, 1983, pressure tubes — which hold fuel rods — ruptured due to hydriding at the Pickering reactor 2. Some coolant escaped, but was recovered before it left the plant, and there was no release of radioactive material from the containment building. All four reactors were re-tubed with new materials (Zr-2.5%Nb) over ten years;[48]
On August 2, 1992, a heavy water leak at Pickering reactor 1 heat exchanger released 2.3 petabecquerel (PBq) of radioactive tritium into Lake Ontario, resulting in increased levels of tritium in drinking water along the lake shoreline;[5]
On December 10, 1994, a pipe break at Pickering reactor 2 resulted in a major loss of coolant accident and a spill of 185 tonnes of heavy water. The Emergency Core Cooling System had to be used to prevent a core meltdown.[50] It has been called "the most serious nuclear accident in Canada" by The Standing Senate Committee on Energy, the Environment and Natural Resources in 2001.