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CP1 - The first nuclear pile.
Also CP2, Site A and Plot M
As is the case with many large American cities, Chicago has spawned it's share of run down, dirty and dangerous areas. I have visited the city many times, as I am only an hour or two away, and have come to know, that there are certain areas where you just don't go. Still, there is a mix, and it is surprising what you can find. As in New York, in some places, only a few blocks separates the good from the very bad. One of these areas is the location of the University of Chicago. Much of the surrounding neighborhood has turned bad, poor, run down, and dangerous; but the campus itself is quite a contrast to it's surroundings, and a pleasant place for the privileged few who attend the university.
Within this extensive campus stands a large sculpture, on the east side of Ellis Avenue between 56th and 57th, wedged in between the Max Pelevsky Dormitory, and the tennis courts. Henry Moore, sculptor, named this work simply Nuclear Energy. The twelve foot high modern, metal sculpture stands within a concrete plaza, and may strike the visitor as nothing special, just another scrap of oddly shaped modern art; but it marks one of the milestones in a project which was to change history, and remake the world. This place was a part of the Manhattan Project, and of the development of the atom bomb, and of nuclear energy.
Generally, when people think of the development of nuclear energy, and of the atom bomb, visions of the Trinity site come to mind, or of Oak Ridge, Los Alamos, or possibly Hanford; but these places came latter, and were primarily chosen for their isolation. Chicago played a much larger role than most people realize, in the development of nuclear technology, as it still does. Even today, two of the largest nuclear physics facilities, Fermilab, and Argonne, are located on the outskirts of Chicago.
The sculpture marks the site of the first controlled nuclear reaction. This reaction took place in what was called a nuclear pile; but which we today would call a nuclear reactor. It was the work of Enrico Fermi, and others, and was the culmination of the old experimental, philosophical physics, and the beginning of the new more hard edged practical physics. The gentleman physicists of the previous several generations were about to be replaced by a new breed, just as a century before, they had themselves replaced the old physicist/philosophers. Also due for replacement was the old Stagg Field, built at the turn of the century. Stagg field was torn down in 1957, including the stands under which the first pile was constructed. There is a new Stagg Field now, several blocks from this original site. One could have wished that they would have preserved at least the grandstands under which the pile was built; but this was not to be.
The whole story is pretty fascinating, and yet it is only a single chapter in the development of nuclear technology. The site was chosen in part, due to a strike, which interfered in the construction of the pile. This first reactor was an example of primitive engineering, allied with advanced science. Men stood above the structure, armed with buckets of bromated water, prepared to douse the reactor, should things get out of hand. The structure itself was built from bricks, rods, and pellets. An assortment of scientists, military people, and various others stood on a stand above the floor where the pile stood, awaiting the results. The whole thing was top secret, and there are thus no photographs of this very historical event; but sketches, and artists depictions were latter drawn. Future events were more carefully recorded by what would then be a much more secure and confidant nation. Trinity was exceptionally well recorded, as was the loading and dropping of the first nuclear weapons, and the countless nuclear tests to come.
A cadmium plated rod was slowly
withdrawn, by scientist George Weil, while every ear was cocked in rapt
attention, straining to hear the faint clicks from a radiation counter. Though
accounts vary, giving the moment of criticality as having occurred anywhere from
3:20, to 3:48, according to the official record, it was at , on
CP1 was a relatively large and heavy structure, and quite primitive, by today's standards. It nearly filled the 30 x 60 foot squash courts in which it was assembled. The framework was built of wooden timbers, which supported the actual reactor components. These components consisted of about 400 tons of graphite bricks, along with fissionables. The energy came from over six tons of uranium, along with another 34 tons of uranium oxide. The unit was designed to be roughly spherical, or at least as spherical as a structure made of bricks, and laid down by scientists could be. The wooden timbers supported the narrower bottom portions of the squared off sphere, keeping the structure from collapsing. The upper layers needed no support. A large, square balloon, hung over the structure. This is the simplest, and most easily constructed, of all of the reactor types, and is also the most dangerous.
The fissionable materials were placed, as pellets, within the cavities of the graphite bricks. The graphite acted as a moderating material, slowing down the neutrons so that they could react with the uranium. This is the same material as is used in pencil leads, and is very slippery. The graphite bricks were constructed in a special workshop, and were machined with a pair of holes in each, so that each could contain two pellets of uranium oxide, or in some cases two pellets of actual uranium metal. The pellets were about the size and shape of hockey pucks. Fabricators, who worked on the project, commented that walking across the floor of the shop in which these bricks were made, was like walking across a skating rink, because of the graphite dust everywhere. A photo of one of the original bricks, on display at Argonne National Laboratory, is shown at right.
Today, such a structure would not be allowed in the center of a major city; but this was wartime. By today's standards, this was an incredibly dangerous, insecure, and dirty device. America has not built a graphite reactor since the forties, though this is the design most often found in the former Soviet Union. There was nothing like radiation shielding, no facility for cooling, and no barrier other than the surrounding balloon, to keep any escaping nuclear particles inside. Though there was no danger of anything like a nuclear explosion (which requires quite a different kind of containment), there is always the possibility of meltdown, or release of nuclear materials, as well as the radiation danger. A graphite moderated reactor also adds the danger of fire, since graphite will catch fire if sufficiently heated. What the team did have in place was a sort of a Rube Goldberg series of safety precautions. There was a set of electronically controlled rods which would be automatically pushed into the pile, at certain levels of radiation. There was also a rod weighted to be pulled into the reactor, and held off by a rope. In the event of emergency, Dr. Norman Hillberry was standing by with an axe, to cut the rope. Finally, above the reactor stood three other scientists, with buckets of a cadmium salt solution, with which they would douse the structure, at any indications of danger.The site today is nothing very spectacular, unless you know it's history. Still, it is well worth a visit, if you happen to pass anywhere near. Unlike most other nuclear related sites, a visit is a simple matter. You park your car, or get out of your cab, and saunter over. If you happen to be up at Argonne National Laboratory, there is even a shuttle bus, which stops nearby. The place gets little attention, these days, and many of the locals do not even know what is signified by the statue. The nuclear materials only stood on this spot for a short time. Due to safety, and security considerations, the pile was dismantled, after a few months, and reassembled at a spot over twenty miles outside of town, which was latter to give birth to Argonne National Laboratory. Eventually, due to their radioactivity, the materials would be buried on an Illinois hillside, the original site of the labs, and of the reactor; laid to rest as it were. Argonne National Laboratory has a model of the CP1 reactor, which is shown in photo to the right.
For the determined nuclear tourists, a visit to this nearby hillside might be in order. Officially, the spot is know as Site A, with a nearby area known as Plot M, and is a public space. As a matter of fact, you can go and have a picnic on the spot, if you like. There are bike trails and picnic areas all around the hill, as it is a part of a park preserve. The monitoring teams come to visit, every so often, and check levels of radiation, and of various chemicals.
Buried at this spot are the remains of the first two nuclear reactors, which used the same nuclear materials. In February of 1943, for a number of reasons, CP1 was disassembled, and moved, to a spot about 25 - 30 miles outside of town, in the Argonne woods of the Pallos Park area, where it was reconstructed as CP2, in March of 1943. CP2 was essentially a reconstructed CP1, with a few safety improvements, some radiation shielding, and a more solid permanent structure. Bomb materials were actually produced by reactor, CP2, as well as by several others. The remains of CP2, and thus CP1, are encased in a concrete vault, and offer no radiation danger, in their present state. This site is about three miles from the present location of Argonne National Laboratory, in what is now a nature preserve.
As with the site of CP1, the old Argonne National Laboratory, including the entombed remains of reactors CP1 and CP2, gives little indication of what it once was. As with the site on Ellis, there is nothing left but a marker, placed at the sites after the fact. What is truly amazing about the Pallos Woods section is how quickly and completely the woods have once again made the site their own. Without the markers, or a good map, you would never know what had once stood here. For anyone with any interest in the subject, I strongly recommend a visit to all three sites, which can be done in a single, somewhat busy day.
As of this writing, Argonne National Laboratory has weekly tours, usually on Saturday mornings, or afternoons. It is a simple enough matter to visit the woods, either before an afternoon tour, or after a morning tour. These two sites compliment each other nicely. The Pallos Woods area is also quite nice, and is worthwhile just for the pleasant walk along it's shaded paths.