Graduate Thesis Or Dissertation
 

Feasibility of neutron radiographing reactor fuel assemblies

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bv73c370d

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  • Verification of fast reactor safety requires experiments wherein fuel bundles, enclosed in massive steel capsules, are subjected to simulated accident conditions in reactors such as TREAT(16) at ANL Idaho. To date, only small bundles (one to seven pins) have been tested in the experimental series. Determination of the fuel configuration within the capsule has depended on the neutron hodoscope during the reactor power burst and on thermal neutron radiographic techniques for more precise determination before and after the test. The purpose of this study is to determine whether there are neutron radiographic techniques that could provide the nondestructive evaluation capability needed for extension of the experimental series to much larger fuel bundles (e.g., 37 pins to 217 pins) as is projected for the NRC-ERDA fast reactor safety studies program SAREF.(17) There are two parts to the total problem: (1) can an adequate signal to noise ratio be obtained and (2) can the information from such complex geometries be adequately decoded by means, for example, of two or three dimensional image reconstruction techniques. This thesis addresses the first question only. It is shown that neutrons of epi-thermal energy could provide useful penetration and contrast sensitivity. Experiments performed, using pin bundles of simulated fuel designed to give the same neutron attenuation characteristics as fuel of the "Fast Flux Test Facility" (FFTF), confirm that the epi-thermal flux intensity available from a typical TRIGA research reactor is sufficient and that sensitivity can be obtained to at least a single pellet sized axial gap in the center of a 217 pin FFTF fuel assembly. The study includes evaluations of (1) neutron source characteristics, (2) neutron imaging methods, (3) fuel bundle simulation, (4) neutron beam generated fission background and (5) the dependence of radiographic sensitivity on angle of orientation for symmetrical bundles.
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