Patent Number: 039716996
Section: description

The neutronic reactor is constructed upon a concrete base 10, and generally includes a moderator 12 in which fuel elements 14 are disposed, and a shield 16 surrounding the moderator 12. A plurality of parallel coolant tubes 18 traverse the moderator 12, and the fuel elements 14 are slidably disposed upon ribs 20 within the coolant tubes 18. The fuel elements 14 comprise bodies 22 of material fissionable by neutrons of thermal energy encased in a protective jacket 24. A suitable material for the jacket 24 is aluminum, and the thermal neutron fissionable material 22 may be natural uranium, or in the event that it is not desired to convert material to fissionable material, a composition composed of 1 part U.sup.235 to 139 parts of thallium. Control rods 26 are slidably disposed within wells 28 extending through the moderator 12 of the reactor in order to control the neutronic reaction, as is well known in the art. The coolant tubes 18 are provided with caps 30 at the end thereof, and a fluid coolant, generally water may be flown through the tubes 18 in order to cool the fuel elements 14 and the moderator 12 in a conventional manner. A gas-tight envelope 32 is disposed between the moderator 12 and the shield 16 and prevents the ambient atmosphere from infiltrating into the moderator 12 of the reactor. The coolant channels 18 pierce the envelope 32, and are sealed thereto. The gas enclosure 32 is provided with a pair of apertures 34 and 36 on opposite sides of the reactor in order to introduce the gas into the moderator 12. The one aperture 34 is adjacent to the top of the reactor, and the other aperture 36 is adjacent to the bottom of the reactor, as shown in FIG. 1. Pipes 38 and 40 having valves 42 and 44 are sealed to the apertures 34 and 36, the pipe 38 being connected to a source 41 of gas with the moderator material, and the pipe 40 providing an outlet for the gases from the reactor. In the particular construction of the reactor described, the coolant tubes 18 are spaced from adjacent tubes by 83/8 inches. The tubes 18 are constructed of aluminum with an inner diameter of approximately 1.611 inches and an outer diameter of approximately 1.729 inches. A water coolant may be flown through the channels 18. The fuel elements are approximately 1.44 inches in diameter, the outer jacket 24 being approximately 0.028 inch of aluminum and the inner fissionable body 22 being of natural uranium. The moderator 12 is constructed of graphite, forming a cube 25 feet on a side. The copending patent application of Enrico Fermi and Leo Szilard, Ser. No. 568,904, filed Dec. 19, 1944, now U.S. Pat. No. 2,708,656, issued May 17, 1955, discloses a reactor constructed in a manner similar to the reactor described above, and describes the nuclear principles of its operation in greater detail. Carbon dioxide may be introduced into the moderator material through the pipe 38 and exhausted through the pipe 40. Carbon dioxide and carbon react according to the equation EQU C + CO.sub.2 = 2 CO. in order to minimize the deterioration of the moderator, an inert gas is mixed with the reactive gas. Mixtures of helium or carbon monoxide and carbon dioxide have been found to be particularly suitable. A concentration of 40 to 60 percent carbon dioxide by volume with helium under standard conditions of pressure and temperature appears to adequately retard the deterioration of the graphite while inhibiting graphite expansion satisfactorily. It is also to be noted, that carbon monoxide will react with carbon dioxide to form carbon, since the chemical equations above are reversible at suitable temperatures. It has been found that small quantities of carbon monoxide in the carbon dioxide circulated through a graphite moderator of a reactor will also inhibit the deterioration of the graphite described above. The man skilled in the art will readily devise many other modifications and embodiments of the present invention as a result of reading the foregoing disclosure. Hence, it is intended that the scope of the present invention be not limited by the foregoing disclosure, but rather only by the appended claims.