Reflector savings

The bucklings were calculated using pubUshed reflector savings values for slightly enriched uranium. 

The bucklings shown in the table were evaluated from the assumed reflector saving, X, the calculated values of the. semi-axis of the critical assemblies, and the tables of Reference 1. 

The clean critical size, reflector savings, and temperature coefficients were measured tor two 1.8% enriched cores with water to uranium volume ratios of 4.4 and 6.0 (excluding control rod water channels and axial water gaps). In addition the clean critical size was obtained for the 1.59% enriched core. The clean critical size and reflector savings were also measured for the 1.8% cores containing 18% and 14% voids (ratio of void to water plus voids), respectively. The voids were obtained by inserting low density (9 Ib/ft ) foamed polyurethane void simulators between fuel rows to obtain a uniform displacement of water. These simulators are coated to reduce wafer absorption to a negligible value. The measurements are summarized in Table I. 

TABLE IV. Comparison of Reflector Savings with 0.387-ln Rods of 1.3% Enrichment... 

The experiments that have been performed are standard. Critical configurations have been determined for many different compositions. Reactivity coefficients have been determined by period measurements or by use of control rods calibrated by period measurements. Reactivity worths have also been determined analysis of the response to oscillator and rod drop experiments. Rossl-o measurements have been made on a number of assemblies to determine the ratio (rf the effective delayed neutron fractlqn to the prompt neutron lifetime and thus indirect to give information on the neutron spectrum. Detector responses, both as a function of detector material and as a function of position, have been made to determine data relevant to power distributions, bucklings, reflector savings, and neutron spectra. Spectrum measurements have been made by use of ehiulslon plates. 

Table I, due to Hansen and Wood, gives a few reflector savings measured on the plane surfaces of 15-in. and 21-in. diameter U(93). discs, compared with computed values for infinite slabs. 

Buckling and reflector-savings measurements were performed by both the standard flux-shape technique and the "variable loading" technique in which a series of axial relaxation lengths were measured as a function of lattice size and fitted to the equation... 

The reflector savings quoted were computed assuming the lattice boundaries to be the metal direction and half a water gap out in the reflector in the y direction. 

From Table I it can be seen that the reflector savings measured in the x and y directions are the same, but that the "variable loading technique gives values from... 

Differences of this sort have beeii observed before in other BNL measurements using these techniques and there is, in addition, a theoretical basis for expecting a difference in the reflector saving liiferiwd by the two methods. Whether or not the magnitude of the difference observed can be properly accounted for by the theory will be shown by the detailed analysis now in progress. 

Using a one-group critical equation (with constant reflector savings assumed) migration areas of 44.6 cm in radial (M ) and 46.0 cm in axial direction (h were determined. Theoretical value for migration area for this lattice is 42.29 cm using Mercury code in which Deutsch s Method is used. ... 

HANSEN, G. E., et aL, Reflector Savings of Moderating Materials on Large Diameter U(93.2) Slabs, ... 

Reflector savings were computed and are shown in Fig. 1. Experimental values are also shown. The discrepancy at large V q/V is not understood. 

Analysis Of the reflector savings was done with the FOG code, utilizing the 4-group averaged cross sections obtained by the above procedure. 

The. calculations for the poisoned lattices. were also performed and they are also in excellent agreement with the measurements, except for the reflector savings. 

Lattice Spacing (in.) Pu-240 Isotopic Composition (wt%) No. of Rods For Critical Experimental Temperature Calculated Multiplications Reflector Savings (cm) Bucklings (m- )... 

The modified conversion ratio, U-238 to U-235 fission ratio (5 ), U-238 capture cadmium ratio, and thermal disadvantage factor have been measured in the lull range of lattices, while critical bucklings and reflector savings liave been measured in the looser assemblies. The measurements of lattice and ceU parameters were carried out as previously described. ... 

Lattice. Pitch, cm Clad H to U-238 Atom Ratio Critical Bucklins cm X 10 Radial Reflector Savings, cm 6 Modified Conversion Ratio ... 

BENNETT, R. A., and E. Z. BLOCK, Reflector Savings of One Per Cent Enriched Uranyl-Nltrate, Nuclear Physics Research Quarterly Report Oct, Nov., Dec, 1957, HW-54591, (March 5,1958). 

The results for k jj at the Best Bm values and the calculated and measured values for reflector savings x are shown in Table I. The measured and calculated results iat p and are shown in Table n. 

An additional comparison of the data io calculated critical masses was made in spherical geoketry. Radii of equivalent spheres were obtained by equating bucklings in spherical and the experimental rectanguto geometries in which appropriate values of the extrapolation distances and reflector savings were used. The masses derived... 

Critical parameters for low enrichment uranium rods are usually for lattices with optimum moderation and full reflection by water. When uranium rods are cleaned or dissolved in nitric acid, a more efficient neutron reflector, uranyl nitrate, is produced. This difference (increased reflector savings) should be considered in deriving safe process controls, for example, if additional batches are processed in the same bath. 

Reflector savings for water reach a maximum at 6 in., but for uranyl nitrate the savings continue to increase significantly with thickness, particularly as enrichment and concentration increase. The results (Tables i and n) are based on 20-ln.-thick uranyl nitrate refledtori but they should be reliable for all thicknesses to 5.0% "tI with concentrations to 200 g U/liter or to 2.0% U with concentrations to 1000 g U/liter since the... 

Batteller Northwest study indicated reflector, savings approach a maximum under these conditions. jNote that, at enrichments >2.1% 0, the uranyl nitrate, (reflector), can attain criticality. ... 

C. A. ROGERS. R. C. LLOTO, S. R. BIERMAN, iand E. D. CIJIYTON, Reflector Savings for Uranyl Nitrate Low Enrichment, BNWL-1258, Battelle-Northwest Laboratory (November 1969).. 

Additional measurements were made using a mockup of the dump valve and a water-filled top reflector plug to determine the reflector saving difference between the experimental conditions and 15-cm water reflection. 

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