By Earl Hunsinger
Nuclear power is considered by many, to be complicated and dangerous. The use of radioactive materials certainly has the potential to be dangerous. The radioactive waste produced by this use is even more potentially dangerous, if only because of the need for safe, long term storage. However, as far as being complicated, nuclear power plants are only complicated, because of the redundant safety measures used.
Many people would probably be surprised to learn that in itself, the generation of power from radioactive materials (uranium), is not complicated at all. In many ways it is simpler than burning coal. The very name given to the material used implies this simplicity. The uranium, which is the heart of the power plant, is often called a nuclear pile. The history of the first nuclear pile illustrates why this is so, along with the simplicity of this most feared source of power.
On September 12, 1933, the famous physicist Lord Rutherford was quoted in The Times of London as saying that, anyone who looked to the atom as a potential source of power was "talking moonshine." As the Hungarian theoretical physicist Leo Szilard later said, "Pronouncements of experts to the effect that something cannot be done have always irritated me." As a consequence, as Szilard stopped on a street corner in London's Southampton Row waiting for the light to change, he was thinking of how Rutherford might be proved wrong.
As the light changed to green and he began to walk across the street, he realized that the solution was to find an element that would be split when struck by neutrons and would release two neutrons for every neutron that it absorbed. With a large enough quantity of this element, a chain reaction could be created, with two neutrons becoming four, four becoming eight, and so on. This simple, yet profound insight, would lead to nuclear power plants, and their more sinister cousins, atomic bombs.
Eventually, it was discovered that uranium could be used to sustain the type of chain reaction that Szilard had envisioned. By 1942, the world was engulfed in war, and the Manhattan Project had begun. The scientists working on this top secret scientific project had been given with the task of building the world's first atomic bomb. As part of this work, the Italian immigrant and physicist Enrico Fermi, was leading a group of scientists (including Leo Szilard) in the construction of the world's first nuclear reactor.
The site chosen for the experiment was a squash court under the football field at the University of Chicago. Blocks of graphite and uranium were laid in a circular pattern on the floor of the court. The plan was to stack these blocks so that they eventually formed a sphere (literally a pile) with a radius of approximately thirteen feet. Cadmium rods were added as the blocks were stacked. These would absorb neutrons and so stop the chain reaction.
According to the University of Chicago website, when the last of the cadmium coated rods was withdrawn at 3:25 pm on December 2, 1942, the world's first self sustaining nuclear chain reaction was initiated.
The reactor, also known as Chicago Pile-1 (CP-1), had very few safety devices. The book, The Making of the Atomic Bomb, by Richard Rhodes, estimated that if the scientists present on that day had allowed the chain reaction to continue for an hour and a half, the reactor would have reached a million kilowatts. Long before that, it would have killed them all and melted down. The only safety systems that they employed consisted of the spare cadmium rods suspended over the pile of uranium by a rope, with a man standing by the rope with an ax, ready to cut it if things got out of control.
According to Paul W. Frame of the Oak Ridge Associated Universities, the safety term SCRAM, which refers to the sudden shutdown of a reactor, pays homage to this man. SCRAM is said to stand for "safety control rod ax man."
Present day nuclear reactors are much more than just a pile of uranium and graphite bricks. Steam is produced from the heat generated by the chain reaction. This steam is used to turn turbines, which are in turn used to generate electricity. Extensive shielding is built around the radioactive material and elaborate safety systems are installed. Still, as complicated as these systems are, the basic principle remains the same, as it was way back then in that squash court.