12 December 1952. 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 subsequent 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. Subsequent monitoring of surrounding water sources revealed no contamination. After the incident, approximately 1202 people were involved in the two-year-long cleanup. 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 U.S. Navy, was among the cleanup crew.