Oct. 22, 1957 E. P. WIGNER ETA 2,810,689 FLUID MODERATED REACTOR Filed Nov. 6, 1945 5 Sheets-Sheet li - - - - - - - - - - -a- - - -a - - - - Parana - - - k SSSX sateagazzazz Bill.R | S. |||||| till s: Hill|| | | | | N Z t222222a2ateS 22.97e2e 1 Z2/29-zer -4C22 -2°. (22/zza2-e-r -724/2ZZ4724-et 12, 222-2222/22/22e t22227.2e2/. Oct. 22, 1957 E. P. WIGNER ET AL 2,810,689 FLUID MODERATED REACTOR Filed Nov. 6, 1945 5 Sheets-Sheet 2 FIG 2 s /722/2/Z ZoZrs. 22eze 122/292/zer 225-222 Z22er (242 v22.2%67 222/2 22 -126/2ZZe22 Oct. 22, 1957 E. P. WIGNER ET AL 2,810,689 FLUID MODERATED REACTOR Filed Nov. 6, 1945. 5 Sheets-Sheet 3 Q.©OooOcolooooo9po 1722/2Zz ao Zrs. 4/22zzesses: $RN §§§§ \\$}}?! 2%. h Q\\§§§ §§§§ ise §§§§§ ?? Oct. 22, 1957 E. P. WGNER ETAL 2,810,689 FLUID MODERATED REACTOR Filed Nov. 6, 1945 5 Sheets-Sheet 4 %WASIZ ES2 s 2 MXY SS2 2 2 % S. se s 4.& ear 12z/2Z Zors: 4229/e/ze Z Z2/2 ze 2/222aesses: FIES 1e o 216 2%27. 7:42.72 222/zza22e CA222222az Z/2Zzaez2 2. 532, -2/ 124-1242% e-4- --zeez. Oct. 22, 1957 E. P. WIGNER ETAL 2,810,689 FLUID MODERATED REACTOR Filed Nov. 6, 1945 5 Sheets-Sheet 5 /7Z z/2ZZ 422s. 22.9ese 122/2S22e2 2eed af. (2242-22ezr 47222 MX122279 222-22. 1 2/222avezr was ze (2/2e2/. - * 2,810,689 United States Patent Office Patented Oct. 22, 1957 1. 2 Fig. 6 is a further modification of a plug shown at the top of the structure shown in Fig. 2; and 2,810,689 Fig. 7 shows the helium circulating system embodied in Fig. 1. FLUID MODERATED REACTOR Referring more particularly to Figs. 1 and 2, numeral Eugene P. Wigner, Leo A. Ohlinger, Gale J. Young, and 1 denotes a reactor of a neutron chain reacting system Alvin M. Weinberg, Chicago, Ill., assignors to the having an active portion contained within a cylindrical United States of America as represented by the United tank. 2 of aluminum, or other suitable non-corrodible States Atomic Energy Commission material, relatively non-absorbing with respect to neu Application November 6, 1945, Serial No. 627,070 O trons, said active portion comprising a plurality of rods 3 of fissionable material, such as uranium, uranium oxide, 1 Claim. (Cl. 204-193.2) or other compounds of uranium, suspended in a neutron slowing fluid (i. e. moderator) contained in said tank, for example, deuterium (i. e. heavy hydrogen), or deu The present invention relates generally to neutronic 5 terium oxide (D2O) commonly known as heavy water. reactors having liquid moderators, and more particularly Broadly, such a liquid moderator type reactor is well to neutronic reactors having liquid moderators in which known now as is shown by the above mentioned Fermi the reactor is cooled during operation by a circulated and et al. patent. Alternately, a deuterocarbon material op cooled liquid moderator, and to means and methods of erated at high temperature or heated by external heating cooling such a reactor through circulation and cooling 20 means (if non-liquid at lower temperatures) may be used of the moderator. as a moderator, since it is essentially a hydrocarbon with In neutronic reactors, a neutron fissionable isotope, its hydrogen in the form of deuterium, the deuterium such as U233, U235, or 94289 or mixtures thereof, is sub content being useful in slowing neutrons. The tank 2 jected to fission by absorption of neutrons, and a self is substantially filled with the moderator and has sufficient sustaining chain reaction is established by the neutrons 25 heavy water so that the active portion of heavy water with evolved by the fission. In general, such reactors com the immersed uranium exceeds the critical size (that prise bodies of compositions containing such fissionable is, the size wherein the rate of lose of neutrons from material, for example, natural uranium, disposed in a the outside walls of the reactor equals the rate of gain neutron slowing material which slow the neutrons to of neutrons in the heavy water uranium active portion thermal energies. Such a slowing material is termed 30 of the reactor of the neutron chain reaction system). a neutron moderator. Carbon, beryllium, and D2O Such critical size can be forecasted by taking measure (heavy water) are typical moderators suitable for such ments and plotting, for example, the reciprocals of neu use. Heat is evolved during the reaction which in reac tron density at a certain point in the reactor tank as tors heretofore known is removed by passage of a coolant ordinates against Some measure of the overall size of through the reactor in heat exchange relationship there 35 the uranium heavy water active portion (e. g. the level with. Specific details of the theory and the essential to which the heavy water has risen in the tank) as characteristics of such reactors are set forth in the copend abscissas as the size is being increased by raising the ing application of Enrico Fermi and Leo Szilard, Serial level of heavy water in the tank. From these values, a No. 568,904, filed December 19, 1944, now U. S. Patent curve will be obtained which when extrapolated will in No. 2,708,656, dated May 17, 1955. - 40 dicate in advance or forecast what the critical size will Hence, an object of the present invention is to pro be before it is actually reached. This critical size will vide a novel neutronic reactor of the liquid moderator occur at the point where the curve crosses the axis of the type in which the moderator is circulated and cooled and abscissa. This method of determining critical size in ad employed as the cooling medium for the fissionable mate vance was discovered prior to this invention. rial. 45 Each of the uranium rods 3 is preferably sheathed in Another object is to provide a novel cooled self-sustain aluminum or other suitable non-corrodible material rela ing chain reacting system of the liquid moderator type tively non-absorbent to neutrons, closely fitting the rods having relatively high neutron densities and incorporat to provide good heat transfer. These sheaths prevent ing novel cooling means having a minimum of impurities passage of fission fragments from the uranium into the so that the system is of relatively smaller size as com 50 heavy Water, to prevent the heavy water from becom pared with known systeins of similar type. ing highly radioactive. Each rod 3 is suspended by a Another object is to provide novel means for cooling supporting cable 4 in a cylindrical tube 5 of a substan a neutronic reactor of the liquid moderator type. tially non-corrodible material having low neutron absorb Another object is to provide a novel method of cooling ing characteristics such as, for example, aluminum, a neutronic reactor of the liquid moderator type. 55 beryllium, or lead. The upper end of cable 4 is sup Other objects and advantages of the present invention ported by an eye 6 extending through and having an are apparent from the following description taken in upper counterpart above, a plug 7 sealed to a distributor conjunction with the accompanying drawings, in which: head 8, by a screw threaded collar 7a, the head 8 being Fig. 1 is a diagrammatic vertical central sectional view, in turn sealed to the upper end of tube 5. By such partly in elevation, of a self-sustaining neutron chain 60 construction, each rod 3 is readily replaceable by merely reacting system involving the present invention; dropping a hook or other suitable tool from a crane Fig. a is an enlarged top view of the control rod or other lifting device (not shown) after unscrewing the shown in Fig. 1; collar 7a to engage the upper part of eye 6, so that the Fig. 2 is an enlarged sectional view of one of the rod 3 can be lifted with the cabie 4. Tube 5 extends 65 through a sleeve 9 in a radiation shield 10 (which pre uranium rods and Surrounding tube shown in Fig. 1; vents undesired biological effects as explained below) Fig. 3 is a Sectional view taken along line 3-3 of and is Sealed to the upper end of sleeve 9 by a gas-tight Fig. 1, Selected elements being shown in elevation for stuffing box 11 to prevent the escape of heavy water clarity; vapor and helium gas present in the tank as is herein Fig. 4 shows a modification of the plug used at the 70 after described. top of the structure shown in Fig. 2; The shield 10 comprises a series of spaced iron plates Fig. 5 is a top view of the plug shown in Fig. 4;. having cooling water flowing therebetween as indicated 2,810,689 3 4. by arrows in Fig. 1. The effect of the shield 10 is to weight of an element the better it serves as a shield for slow neutrons and to absorb gamma rays. More spe penetrating radiations, such as gamma radiations. Lead cifically, iron is more effective than most metals to slow of a particular thickness is, therefore, an excellent shield fast neutrons by inelastic collisions. In such collisions, for certain purposes while water of the same thickness the neutron energy is used up in producing an excited is only fair, for example. However, thick water shields state of the iron nucleus which later emits energy as are convenient and satisfactory.