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Cominco had produced electrolytic hydrogen at Trail, British Columbia, since 1930. Urey suggested in 1941 that it could produce heavy water. To the existing $10 million plant consisting of 3,215 cells consuming 75 MW of hydroelectric power, secondary electrolysis cells were added to increase the deuterium concentration in the water from 2.3% to 99.8%. For this process, Hugh Taylor of Princeton developed a platinum-on-carbon catalyst for the first three stages while Urey developed a nickel-chromia one for the fourth stage tower. The final cost was $2.8 million. The Canadian Government did not officially learn of the project until August 1942. Trail's heavy water production started in January 1944 and continued until 1956. Heavy water from Trail was used for Chicago Pile 3, the first reactor using heavy water and natural uranium, which went critical on 15 May 1944.