Two Seconds

The world's first controlled nuclear chain reaction took place beneath the bleachers of Stagg Field at the University of Chicago. Under the direction of Enrico Fermi, lumps of uranium were dropped into holes in graphite blocks. Fermi's first experiments toward building a functioning nuclear reactor involved using blocks of graphite. It's mostly carbon and it's a very good moderator. To make a nuclear reactor you need to slow the neutrons down. You can't use the neutron as it comes off of a fission reaction. It's going too fast. In a bomb you want fast neutrons, but in a reactor you want them slowed down. But even slowed down, a nuclear chain reaction produced incredible amounts of heat. Without a way to cool the Chicago pile, its only use was for demonstration. There was a really short period of time between the demonstration of a chain reaction by Fermi and the design of this reactor. So people were sort of learning as they went. And so they were continuing to experiment at Chicago where the first chain reaction was done. There was really a team of people. The scientists at Chicago and the DuPont engineers working together to build this first of a kind reactor. As a moderator, the Germans had abandoned graphite in favor of heavy water, but the American effort followed Fermi's lead and stuck with graphite. The advantage graphite had there was you could build a block, a reactor out of graphite, and the graphite could support the fuel and all the cooling tubes and everything else. Heavy water was of course just water and you had to introduce all kinds of other vessels there to contain the water and contain the fuels. The challenge was how to cool the reactor. The Columbia River offered the most accessible solution, water. But even water can hamper a nuclear chain reaction. So the mission was to use as little water as possible, which meant moving it through the reactor at great speed. This is where Hanford's maze of pipes and armies of pumps came into play. As if shot from a pistol, water was sent screaming through the reactor, traveling the full 40 feet, front to rear, in only two seconds. Too cool.