INTEGRAL AND DIFFERENTIAL MEASUREMENTS AS TESTS OF NEUTRON DIFFUSION CALCULATIONS IN THE PURDUE UNIVERSITY FAST BREEDER BLANKET FACILITY
Abstract
The Purdue University Fast Breeder Blanket Facility (FBBF) was designed as a realistic mock-up of the radial blanket of a fast breeder reactor. Measurements made in the FBBF blanket can be used as benchmark tests of calculational methods used in the design of fast reactor blankets. Integral and differential measurements in the FBBF were used to test the accuracy of a two-dimensional diffusion calculation of the neutron flux. Neutron reaction rates for ('238)U capture, ('55)Mn capture, ('232)Th capture, ('197)Au capture, ('186)W capture, ('115)In capture, and ('115)In inelastic scattering were measured by activation analysis in three different blanket configurations of the FBBF. Circular metal foils were irradiated between the pellets in the blanket fuel rods. The absolute activity produced in each foil was measured with a Ge(Li) spectrometer system. Various corrections were made to the foil activities and absolute reaction rates for the infinitely dilute target material were obtained. These reaction rates and previously measured fission rates and neutron spectra were compared with the results of the two-dimensional neutron diffusion calculation. The calculated absolute integral reaction rates compare favorably with the absolute measurements in the inner part of the blanket. The calculated results diverge from the measured results with increasing penetration into the blanket. Three possible areas of deficiency in the calculations were identified. First, the neutron number density appears to be underpredicted by the calculation with the errors compounding across the blanket. Second, the calculations overestimate the low-energy portion of the neutron spectrum when compared to the measurements. Third, mutual shielding of reaction resonances in the detector foils by ('238)U resonances appear to cause difficulties with some reaction rates that are not adequately handled by the calculations.
Degree
Ph.D.
Subject Area
Nuclear physics
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