be held under high pressure to allow it to reach higher temperatures. This allowed the fuel tubes to be made thinner, reducing the number of neutrons lost in interactions with the tubing, and further increasing the neutron economy. The reactor had vertical fuel channels, in contrast with the normal CANDU arrangement where the tubes are horizontal. The reactor did not use conventional control rods, but relied on control of the level of the heavy water moderator to adjust the power output. The reactor could be shut down quickly (SCRAMed) by the rapid dumping of the moderator. Commercialization In 1971 AECL initiated design engineering of a 500 MWe CANDU-OCR, based on uranium carbide fuel. Carbide fuels would corrode in water but not the oil coolant. Carbide fuels were much easier to produce than the more complex ceramics being used in most reactor designs. This design effort was shut down in 1973, but WR-1 tested the concept anyway. Another possibility was to use metallic fuel, which would increase the density of the fuel and offer higher burnup. The metallic fuel conducts heat better so that a higher power core could be used in the same space. Accidents In November 1978 there was a major loss-of-coolant accident. 2,739 liters of coolant oil leaked, most of it into the Winnipeg River. The repair took several weeks for workers to complete. There was another leak in 1980 of 680 liters. Status WR1 was shut down for the last time for economic reasons, on May 17, 1985 although it was the youngest of AECL's large research reactors. The reactor is in an interim decommissioning stage, defuelled and largely disassembled. The site will be returned to greenfield status at the end of decommissioning. See also Gentilly Nuclear Generating Station, a boiling-water cooled CANDU reactor Notes References Bibliography External links The Canadian Nuclear FAQ AECL - Atomic Energy of Canada Limited Atomic Energy of Canada Limited Whiteshell Reactor No. 1 WR-1, UNIQUE AMONG RESEARCH REACTORS Canadian Nuclear Association Nuclear research reactors