Analysis of the Clean Bucklings of 1.3 Per Cent Enriched Uranium-Water Lattices

The experimental results on the relaxation lengths of the clean, 0.6" diameter, 1.3 per cent U235 enriched uranium-water lattices have been completed for the 2:1, 3:1, and 4:1 water to fuel volume ratios. A re-determination of the relaxation lengths of the 1.5:1 lattices as a function of the size of the assembly is presently being carried out. Similar work for the 1:1 water-uranium hexagonal lattices is awaiting the fabrication of the appropriate tube sheets. On the basis of the experimental results obtained to date, we have investigated some of the questions relating to the accuracy with which the bucklings of these water lattices can be determined. The standard method of finding the buckling of thermal reactors in the past has involved the fitting of radial flux traverses to determine the lateral reflector savings of the assembly. The method has thus far proved impractical in view of the small size of our enriched uranium-water assemblies. Experimental values are required of the reflector savings correct to about 0.1 cm as a function of loading, azimuth and distance from the source plane. The variation with azimuth is expected because of the irregular loading patterns, and radial flux harmonics will exist near the bottom and top of the assemblies. However, with the recent foil techniques perfected by Kouts and his group, it may prove feasible to use this method of analysis on some of our larger assemblies.