Patent Number: 039740285
Section: description

Referring to the drawings, the invention will be described as embodied in a water cooled, graphite moderated uranium reactor in which the uranium is in the form of aluminum jacketed short rods, sometimes called slugs, positioned end-to-end in horizontal coolant carrying passages in the graphite moderator. Such a reactor embodying liquid cooling for high power outputs, up to 500,000 kilowatts, for example, is shown in FIGS. 1 and 2. Specific features of this reactor are more fully described, and claimed in the application of Edward Creutz et al., Ser. No. 574,153, filed Jan. 23, 1945, now Pat. No. 2,910,418 dated Oct. 27, 1959. The reactor proper comprises a cylindrically shaped structure built of graphite blocks 1. The reactor is surrounded with a graphite reflector 2 forming an extension of the moderator and is enclosed by a fluid tight steel casing 3, supported in I beams 4 within a concrete tank 5, erected on foundation 6. Tank 5 is preferably filled with water 7 to act as a shield for neutrons and gamma radiation. The encased reactor is surrounded on all sides except one by the water 7, and the side not surrounded, which is to be the charging face 8 of the reactor is provided with a shield tank 9 filled, for example, with lead shot and water. Coolant tubes 10, preferably of aluminum extend through the adjacent concrete wall 11, through shield tank 9, through the graphite moderator blocks 1 to an outlet face 12 of casing 3 to empty into water 7 in tank 5. Only a few tubes 10 are shown in FIG. 1 for sake of clarity of illustration. On the outside of tank 5 where the coolant tubes 10 enter the reactor, the ends of the coolant tubes are removably capped, and are supplied with coolant under pressure from conveniently positioned manifolds. Thus water can be passed through tubes 10 to be discharged at outlet face 12 into tank 5. Water, after having passed through the reactor is removed through outlet pipe 13. The coolant tubes 10 may then be charged with short aluminum jacketed uranium slugs by uncapping the tube to be loaded and pushing slugs into the tubes in end to end relationship by a loading mechanism 14. The reactor can be loaded with sufficient uranium to make the reactor operative to produce high neutron densities, the heat being dissipated by the coolant circulation. This coolant may be water, for example, from a source such as a river, passed once through the reactor, and then discarded, or, the water may be cooled and recirculated in a closed system. Some of the dimensions of one reactor which has been successfully operated are as follows: overall dimensions of the moderator EQU 36 ft. wide .times. 36 ft. high .times. 28 ft. deep reflector -- 2 feet thick PA1 cooling tubes -- 2004 in number PA1 cooling tubes inside diameter 1.611 inches PA1 annular water space -- 0.086 inches. With 1500 central water tubes 10 filled to capacity with uranium slugs, two hundred short tons of uranium are contained in the reactor. This loading of 1500 tubes will make the reactor considerably above critical size and provide an excess reproduction ratio. (Critical size is the size at which a reactor is just chain-reacting and the reproduction ratio is 1). As has been explained, if all of the 1500 tubes are loaded full length with uranium the power in the form of heat generated in the central tube becomes the limiting factor in operation. The power developed will follow a curve similar to curve Y in FIG. 4. However, in accordance with the present invention, the reactor may be loaded with less fissionable material in the transversely central passages than at the edges, in which case the power curve may be similar to curve X of FIG. 4. It will be noted in FIG. 4 that the ratio of heat in a tube disposed L feet from the center of the reactor to heat in the average tube is plotted on the ordinate and the ratio of the distance of a tube L feet from the axis to the total radius of metal is plotted along the abscissa. The amount of excess reproduction ratio that is available when the 1500 tubes of the reactor are fully loaded with 200 tons of uranium will determine the amount of metal that may be removed from the central tubes without making the reactor smaller than critical size. The curves shown in FIG. 3 depict the lengths of uranium metal from the shortest loaded tube at the axis of the reactor to the longest loaded tube 10 near the periphery of the active zone. The dotted line represents the greatest effective length of uranium which the reactor will hold. Curve A shows a loading design for a reactor, as described, which if it contained 200 tons of metal with 1500 tubes fully loaded would have a reproduction ratio of 1.005 or an excess reproduction ratio of 0.5%. This excess reproduction ratio may be used by loading the 1500 tubes with 188 tons of metal in accordance with curve A where the shortest central tube will be loaded with uranium to an effective length of 540 cms. The remainder of the tube may be loaded with spacers of an inactive material such as carbon or aluminum. Starting with the axial tube, the tubes are loaded with increasing lengths of uranium, as shown in curve A, until the tubes located about 250 cms. from the axis are fully loaded to approximately 760 cms. effective length. The remaining tubes located outside the 250 cms. radius to the outside radius are fully loaded to 760 cms. effective length. The effective length from a point at a distance from each end of the uranium where the neutron density extrapolates to zero. It is slightly longer than the actual length; the difference between actual and effective length depending on the efficiency of the reflector 2. A reactor loaded in accordance with curve A under optimum conditions will yield 318 megawatts. Curve B depicts a proper loading for a reactor which when 1500 tubes are loaded with 200 tons of uranium would have a reproduction ratio of 1.0106 or an excess of 1.06%. With only 177 tons of uranium loaded in accordance with curve B, the reactor will be chain reacting and capable, under optimum conditions, of delivering 348 megawatts. Thus, it will be noted in comparing curves A and B that with proper loading the power output may be increased although the amount of fissionable material is decreased. This, of course, is due to the flattening of the neutron reproduction curve so that a larger number of the tubes are brought up to or near maximum power. A reactor has been described in which the amount of fissionable material in the central tubes has been shortened in one direction. This will flatten the neutron activity curve along one axis. Provided sufficient excess reproduction ratio is available, it would be possible to change the loading in accordance with the present invention in two dimensions of the reactor, thus flattening the neutron activity curve on two axes. It will be understood that the method and apparatus described are illustrative only. The invention is limited only by the appended claims.