Dysprosium-cadmium

The thermal utilization of the lattice was determined using the known volume fractions of the constituents of a unit cell and the corresponding macroscopic cross sections along with the thermal-neutron distrlbutitms in these constituents. The distributions were obtained from activations of sets of bare and cadmium-covered dysprosium foils placed in the various parts of the central cell at a distance of 18 in. above the bottom of the assembly where the cadmium ratio no longer varied with height. The value of f obtained was 0.9445 0.0009. 

Flux measurements were made with thorium, cadmium covered gold, and dysprosium foils to provide buckling data at various neutron energy levels. Fine flux structure was Investigated 1 intracell and thermal activations with dysprosium foils. 

Thermal-flux distributions. were measured with. bare and cadmium-covered gold and dysprosium foils. Ther- mal fluxes derived from the two detectors agreed, except near the perturbers Where the disagreement i prOached 10% due to spectral effects. Figure 1 shows t tcal flux distributions at 72% D 0. Agreement with theoretical calculations was generally satisfactory. 

The standard cadmium ratio technique wais used for the measurement of p , the ratio of epi- to subcadmium captures in Th. The 27.4-day half-life Pa produced in ThO, wafers was y counted. The differential technique was used to determine lny> dysprosium thermal disadvantage factor. Dysprosium aluminum foils 1.19-mm diam x 0.127-mm thick were distributed throughout a unit cell. 

Dysprosium-aluminum wire has been chosen to measure the thermal-neutron spatial distribution. Dysprosium has a high cross section for thermal-neutron activation and a convenient half-life of 140 min. Thermal-neutron flux distributions will be made through the glory hole on both sides of core center and along the fine control rod when it is fully inserted. An absolute thermal-flux measurement will be made at the core center with a standard gold foil. This foil will be counted on an end-window GM counter whose efficiency for the standard gold foil has been determined from a previous standard pile irradiation. The results from the two activation detectors will yield the average thermal flux in the reactor core as described in Section II. A cadmium-ratio measurement of AGN-201 fuel can also be made in order to determine the fraction of the total fission rate due to epithermal neutrons. 

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