No description available.

A cadmium-aluminum shield for the V.P.I. subcritical reactor was designed and constructed. Aluminum provides structural strength. Suitable access to fuel and experimental facilities was provided. Experimentally it was determined that the shield is opaque to an influx of thermal neutrons. This is manifested by a depression in neutron density near the boundaries of the pile when the shielded and unshielded region counting rates are compared. The natural-uranium slugs and the highly radioactive source are padlocked within the shield. The assembly is also protected from contamination. Practically no additional biological protection is afforded by the shield due to the neutron-gamma reaction in cadmium. / Master of Science

No description available.

No description available.

Increased conversion ratios and burnup can be achieved by mechanically changing the fuel-to-water volume ratio of a reactor over the core lifetime. As the fuel-to-water ratio decreases, the neutron spectrum softens, thereby increasing core reactivity. Proposed mechanical spectral shift reactors utilize this concept. RFD-1, a 1-dimensional, 4-group code was developed to compute fuel burnup cycles for spectral shift reactors. The code calculates burnup for a triangular core lattice having a beginning fuel to water ratio as high as 1.30. Core shutdown occurs at a fuel to water ratio of 0.50. The microscopic cross sections were obtained through use of the VIM code and tabulated for use in RFD-1 as a function of fuel to water ratio and burnup time. The fission product group cross sections were developed using the VIM and TOAFEW codes. The flexibility of RFD-1 allows the user to study a wide variety of possible core configurations. Results of RFD-1 show that increased conversion and burnup, using lower initial enrichments than that of standard Pressurized Water Reactors, result for mechanical spectral shift designs. The next step is to study specific spectral shift designs in greater detail. The RFD-1 code could be improved primarily through refinements in its cross section data tables. / Master of Science