The McMaster Nuclear Reactor (MNR) is Canada’s most powerful research reactor, providing neutrons for research and medical isotope production. Operational since 1959, it was the first university-based research reactor in the British Commonwealth. Upgraded to 5 MW in the 1970s, MNR has a maximum thermal neutron flux of 1 x 10¹⁴ neutrons/cm²s. Classified as a medium flux reactor, it surpasses other Canadian university reactors, which typically operate at 0.02 MW.