EXPERIMENTAL AND CALCULATIONAL INVESTIGATIONS ON HIGH ENERGY NEUTRON FLUXES AND REACTION RATES IN THE PURDUE FAST BREEDER BLANKET FACILITY (FISSION, THRESHOLD, SCANNING, QUARTZ)
Abstract
The Purdue Fast Breeder Blanket Facility (FBBF) is a source-driven facility which simulates the neutron environment of a fast reactor blanket, allowing calculation-to-experiment (C/E) comparisons to be performed on an absolute basis. Fission rates for ('239)Pu, ('235)U, ('237)Np, ('238)U, and ('232)Th were measured and compared to standard diffusion calculations to provide an improved description and understanding of the high energy neutron fluxes and reaction rate distributions in the FBBF blanket. Fused quartz track recorders were irradiated with fission foils, and automatically analyzed by an image processing system, with a especially developed software, to obtain absolute specific fission rates. The measurements were used as tests of standard two-dimensional diffusion calculations performed with the codes 1DX and 2DB, and the nuclear library LIB-IV. Previously reported deviations between C/E values for ('238)U and ('232)Th fission rates were resolved by reassessing the masses of the fission foils. The C/E values for fission rates are close to unity in the inner part of the blanket and drop off with radius, similar to previously reported trends. The fine structure of the C/E trajectories revealed that the deviations are larger for threshold than for non-threshold reaction rates. They are also larger in the blanket with stainless steel secondary cladding than in the one with aluminum. The sources of neutrons in the calculations were also singled out to allow neutron transmission as well as in situ effects to be separately investigated. The investigations indicated that the underestimation of the transmission of fast neutrons through the blanket causes the C/E deviations to compound with increasing distance from the source. In the outer part of the blanket, where a severe underestimation of the fast neutron fluxes occurs, neutrons born in ('235)U fissions dominate the high energy population, causing the lower and higher energy portions of the neutron spectrum to be strongly coupled.
Degree
Ph.D.
Subject Area
Nuclear physics
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.