X-10

        The X-10 reactor ran from 1942 until 1963. In 1966 it was declared a national landmark. This was not the first reactor, or even the second, though it is arguably the first reactor to be put to practical use. This was, in actuality, a very simple device. It has been described as a piece of twenty first century technology, using twentieth (or even nineteenth) century methods. So what high tech materials, and high tech design features were incorporated into this reactor? Well, the whole thing was constructed of concrete, graphite blocks, pitch (yes pitch, like what you use on your roof), and piping. There was not a mechanical moving part in the whole device, and such a structure could have been built a hundred, or even a thousand or more years ago, had humanity understood the physics involved. A gun, a mechanical alarm clock, or even a doorbell is more complicated than a graphite reactor. At it's most basic, this type of nuclear reactor is simply a collection of regularly spaced tubes, set in concrete, and eventually in carbon (graphite). It is not too far fetched to imagine the early English, or even the Romans building such a device, had they known the theory. Certainly they had the building techniques.
        To make the whole thing work, fuel must be inserted. The fuel used in this reactor is natural uranium. Much has been made of enriched uranium, and various types of nuclear materials for weapons, and power generation. The most common reactor in use today is the light water reactor, which requires reactor grade uranium. Reactor grade uranium is enriched to about 3% U235. Natural uranium only has 0.7% U235, and can not be used in light water reactors. Nuclear bombs require 90% enrichment or better, as do the breeder type reactors, and the fast reactors. Though they have many disadvantages, the one great advantage of the graphite moderated reactor is that it can use regular, non enriched uranium. This was the type of fuel used in this first reactor; really, there was no choice. There would not be sufficient enriched uranium for months, of not years, and that would be used for bomb making. The only other type of reactor which can use natural uranium for fuel is the heavy water reactor, and heavy water is exceptionally difficult to make in the quantities required.
        X-10 was not designed to produce electricity, nor were the other early reactors designed for such a task. So why build them? These early reactors were all designed as a part of the Manhattan Project, to try and build a nuclear bomb. While certain parts of the project labored to separate the small amounts of uranium 235 from the U238 of which most of uranium consists, some scientists theorized that a new element, with an atomic number of 94, would make a great nuclear explosive. This element did not exist in nature; but could be made in a nuclear reactor. What made this such an intriguing possibility, was the idea that this element could be made in a pure isotopic form in a reactor, and then separated by simple chemical means, rather than by the painstakingly slow, and energy intensive methods being used to separate uranium. So this is what the early reactors were designed to do, including the X-10 reactor at Oak Ridge. This new element was eventually to be named plutonium. This is the element that makes up the pits (or cores) of the vast majority of today's nuclear weapons.
        Still, I may have overstated things just a bit. Though the design of this type of reactor is simple, the fuel, and some of the materials used are a bit fussy. The fuel slugs used must be absolutely pure, though they do not need more than the natural 0.7% concentration of U235. Also, the graphite used must be very pure, and free from boron contamination, which was a problem that plagued early American reactor building, and caused the German nuclear program to abandon graphite moderated reactors altogether, and go off on a failed attempt to build a heavy water reactor. Happily for the world, the Germans never were able to produce enough heavy water to build their reactor.


	This is the loading face, of the X-10 graphite reactor. The mission of this reactor was to produce plutonium 239, for possible use in a nuclear bomb. Fuel is loaded in small slugs, that are pushed through the loading face with a metal rod - very high tech.

	An indication of the height of the building. while in operation, a man would stand poised, and the top of the structure, to cut ropes, dump bucket of borated water, and enact the other primitive safety features of the day. Compared with today's boiling water reactors, or high pressure reactors, the old graphite reactors were quite dangerous, and unpredictable. The infamous Chernobyl reactor was of such a design. These make fairly poor power rectors; but are quite good at producing usable plutonium.
	Our guide explains the workings of the reactor. This reactor has been shut down since 1963, and preserved as a monument. However, if it were required, the reactor could be put back in to service.
	The talk is over, and we now have the run of the place. Many wander around; but most will end up climbing the stairs to the control room. At one time, this whole area was open to the public, for casual visitation.
	Up we go, into the control room. This was the very latest in top secret, high tech when it was built 60 years ago. Much has changed since then.
	A couple of last looks at the loading face. Unlike most power reactors, the graphite reactor can be loaded or unloaded, one slug at a time, without shutting the whole reactor down. This is idea for producing plutonium, because you need to get the plutonium out, before it begins to fission as part of the reactor core. This can not be easily done in a modern power reactor, but is quite simple in a graphite reactor. Also note in the photo below, that the entire platform on which the loaders stand is an elevator, allowing them to reach all heights of the loading face.

	Latter on, there were some firefighting and safety modifications added
	On display is the log book, including the entries made when the reactor first went critical.

	A model purporting to show a single loading tube. It can be seen the the concrete loading face serves to keep the tubes aligned, and shields the loaders from heat and radiation. The face is seven feet thick. There is then a three foot wide open air space, which acts as a cooling duct. Finally , there is the graphite core itself, all twenty four feet of it. So the reactor core is merely a block of graphite, holding regularly spaced tubes, into which uranium slugs are pushed by the loaders.
	This model of the reactor probably shows the workings a bit better, and gives a sense of proportion.
	At the back of the reactor stands the core. Just to the rear of the core is a pool, for storage of ejected slugs. Once cooled in the pool, the slugs may be removed for processing, or for separation of plutonium, or radioactive isotopes.
	A look at the side of the model, showing the isotope rooms, where special isotopes may be made through irradiation of various elements.
	Another side view of the reactor model.
	Every student of chemistry or physics will recognize the distinctive shape of the Periodic Table of the Elements. In this case, each compartment has an element sample contained within. Very interesting.
	A container for radioactive fuel.
	This is a major historic site, and is on many registers of historic places. In addition, the site is particularly well preserved.