ANP QUARTERLY PROGRESS REPORT ATED REACTOR . L. Greenstreet D. V. P. Williams Physics Division E. V. Sandin J. W. Nooks Pratt & Whitney Aircraft The second of two critical assemblies of <strong>the</strong> reflector-moderated reactor was constructed as a part of a program presented previously.' The posed of a beryllium reflector and a fuel region of enriched uranium metal and Teflon (CF2)n. The first assembly, an essentially spherical fuel core surrounded by <strong>the</strong> reflector, was described in <strong>the</strong> previous report.2 Since it contained no extraneous structural materials, <strong>the</strong> experimental results could be compared with <strong>the</strong> results of multigroup reactor calculations. The results of <strong>the</strong> second experiment were also to be correlated with <strong>the</strong> calculations, since <strong>the</strong> second assembly, too, was unpoisoned by structure. The assembly has a central polyhedral core, or island, of beryllium about 10 in. in diameter enclosed by a 4.5-in.-thick uranium-Teflon fuel annulus. The fuel is surrounded by an effectively infinite beryllium reflector. Aluminum shells, 0.065 in. thick, separate <strong>the</strong> fuel from <strong>the</strong> island and from <strong>the</strong> reflector and provide structural stability. The assembly is completely described el~ewhere,~ and a summary of its composition is given in Table 4.1. Figure 4.1 is a view of <strong>the</strong> mid-section. The calculated4 critical fuel loading was 7.16 kg of U235, or 0.142 g of U235 per cubic centimeter of fuel annulug. The first critical experimental array of 7.39 kg at a density of 0.146 g of U235 'D. Scott and B. L. Greenstreet, ANP Quar. Prog. Rep. Mar. 10, 1954, <strong>ORNL</strong>-1692, p 45. L 'D. Scott et al., ANP Quar. Prog. Rep. Sept. 10, 1954, <strong>ORNL</strong>-1771. .. p 44. 3B. L. Greenstreet, Reflector-Moderated Critical Assembly Ex erimental Program - Part 11, <strong>ORNL</strong> CF-54- 10-1 19 (Oct. e,, 1954). 4W. E. Kinney, private communication, Oct. 25, 1954. 4. CRITICAL EXPERIMENTS A. D. Callihan Physics Division per cubic centimeter of f about 7.5% excess reactivity. In order to com- pletely fill <strong>the</strong> fuel region without excess control rod poison, it was necessary to decrease <strong>the</strong> loading to 4.66 kg of U235 at a density of 0.092 g of U235 per cubic centimeter of fuel annulus. This latter loading has been shown, by calibrated control rods, to contain 0.92% excess reactivity, equivalent to about 0.31 kg of U235, which gives 4.35 kg of U235 as <strong>the</strong> critical mass of <strong>the</strong> unpoisoned assembly. A series of measurements of neutron and fissionrate distributions and of reactivity coefficients will be made prior to <strong>the</strong> incorporation, in <strong>the</strong> structure, of additional materials to simulate reactor components. TABLE 4.1. COMPOSITION OF SECOND REFLECTOR-MODERATED REACTOR CRITICAL ASSEMBLY Beryllium Island 3 Volume, ft 0.37 Average radius, in. 5.18 Fuel Annulus (exclusive cf aluminum core shells and interface sheets) 3 Volume, ft Average inside radius, in. Average outside radius, in. Mass of (k$ Teflon Uranium u235** Uranium coating material Scotch tape Core Shells and Interface Sheets Mass of aluminum, kg Reflector 3 Volume, ft Minimum thickness, in. Mass of (kg) Beryllium Aluminum 1.78 (50.4 liters) 5.18 9.57 99.38 5.00 4.66 0.05 0.12 5.85 22.22 11.5 1155.0 29.2 *Density, 1.97 g of Teflon per cubic centimeter of fuel annu I us. **Density,0.092 g of U235 per cubic centimeter of fuel annulus. * F f ' . .v' -
Fig. 4.1. Second Reflector-Moderated Reactor Critical Assembly. PERlOD ENDING DECEMBER 70, 7954 53