The purpose of the reactor was to breed plutonium from natural (not isotopically enriched) uranium metal, as uranium enrichment was a difficult process, while plutonium is relatively simple to process chemically. The Y12 uranium enrichment plant required 14,700 tons of silver for its enrichment calutrons, as well as 22,000 employees and more electrical power than most entire states required at the time. Reactor B required only a few dozen employees and fewer exotic materials, which were also required in far smaller amounts. The largest part of the reactor was 1200 tons of graphite used as a moderator, and its power consumption was vastly smaller, requiring only enough electricity to run the cooling pumps.