 However, the Montreal Laboratory had designed and was building pilot reactors, and had carried out some work on separating plutonium from uranium.The Manhattan Project had pursued both avenues, and the scientists who had worked at Los Alamos were aware of work there with composite cores that used both; but there were concerns that Britain might not have the money, resources or skilled manpower for this.In the end, it came down to economics; a reactor could be built more cheaply than a separation plant that produced an equivalent quantity of enriched uranium, and made more efficient use of uranium fuel.