Exponential Measurements

For a monodisperse suspension the decay rate can be described by a first order rate equation. For a polydisperse suspension the decay rate is a sum of exponentials. Measurement of the decay rate permits computation of particle size [338]. 

For the exponential measurements, two lengths of rods were used to make assemblies 150 cm in length. For the 24-cm pitch square lattice, 24 assemblies were arranged on a 6 X 6 array with three assemblies removed from each comer. For 27- and 30-cm pitches, 21 assemblies... 

As part of a Swedish-U.S. exchange program on D3O moderated power reactors, critical substitution measurements were made in the Process Development nie (PDP) of the bucklings of D 0 moderated lattices utilizing fuel assemblies intended for use in the Swedish R-3/Adam reactor. Exponential measurements on these fuel assemblies have been reported in the previous paper.. Each of these fuel assemblies was a cluster of nineteen UOa rods. Complete descriptions of the assemblies have been given. ... 

Many the lattices which were investigated at BNL as subcritical assemblies were also studied in critical assemblies at Westinghouse (Bettis). b some cases the techniques at the two laboratories were similar, and in other cases the techniques were different. There were also a few critical e]q >eriments at BNL. The subcritical experiments at BNL fall. into two classes miniature lattice measurements and exponential measurements. Values of e, p, and f were obtained in small assemblies (miniature lattices) which have a neutron multq>lication of about 3, and in which the central neutron spectrum is characteristic of a critical assembly. Values of M and B were measured in larger assemblies (exponential assemblies) in which the neutron multiplication is between 3 and 50. Thus, there are considerable data to compare reactor parameters as measured in similar lattices by subcritical and critical techniques. 

E. C. Wingfield and E. J. Hennelly, "Exponential Measurements of Natural Uranium Rods in Heavy Water and Comparison With Critical Experiments , Nuclear Sci. and Eng.. 12, 348 (1962). 

ERLANDSSON, L, and R. PERSSON, "Exponential. Measurements on the SRL Four-Tube Fuel Assemblies... 

BAUMANN, N. P., et al., "High Temperature Exponential Measurements and Room Temperature Critical Substitution Measurements on Swedish R3/Adam Fuel Assemblies In Heavy Water, Nukleonik, Band 4, Heft S, (1962). 

E]q>onential and critical-sq>proach experiments were performed on several slightly enriched uranium metal tubes md tube-in-tube combinations in light water. Exponential measurements were, performed on 1) 1.002 wt% U-235 ehriched uranium tubes 2) 1.002 wt% U-23S-enriched tubes containing an inner tube of 1.002 wt% U-235 3) 1.25 wt% U-235-enrlched tubes, and 4) 1.25 wt%U-235-enriched tubes containing an inner tube of 0.95 wt%U-235. Critical-m proach measurements were performed on 1.95 wt%enriched-uranium tubes. The dimensions of the tubes and the results of the ejqieriments are presented in Tables land n. 

Results of Exponential Measurements with Slightly Enriched Uranium Metal Tubes in Light Water... 

The poisoned lattices consisted of a 6 1 ratio of 2.1 wt% enriched uranium 2.33-in.-o.d. tubes and 2.4-in.-o.d. cans containing ground Pyrex glass. Each can was surrounded by a ring of six uranium tubes. Only the 2.8-ln. lattice pitch was measured and seven rings filled the lattice. The exponential measurement Indicates a buckling of 34.04 m" and 140 fuel tubes for criticality (compared to 28.3 tubes for criticality in the 2.8-in. lattice without poison). 

The systems examined were reflected with water. The experimental vessels used were 42 in. in height with diameters of 12, 18, and 24 iii. Critical approach measurements were used to determine the critical height of the assembly containing the 5 wt% B rings, while exponential measurements were used on the other assemblies. 

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