The NRU opened in 1957. On November 3, 1957 the NRU (National Research Universal Reactor) first went critical. This was a natural-uranium fuelled, heavy-water moderated and cooled research reactor (converted to high-enriched-uranium fuel in the 1960s, and finally to low-enriched-uranium fuel in the 1990s). The NRU is a world-renowned research facility, producing about 60% of the world's supply of molybdenum-99, the principle isotope used for nuclear medical diagnosis. Canada also pioneered use of cobalt-60 for medical diagnosis in 1951 and currently the NRU reactor produces the medical-use cobalt-60, while selected CANDU reactors produce industrial-use cobalt-60, comprising 85% of the world's supply. NRU was primarily a Canadian design, and a significant improvement on NRX. Other than radioisotope production, the NRU provides irradiation services for nuclear materials and fuels testing, as well as producing neutron beams for the National Research Council's Canadian Neutron Beam Laboratory.