| Popis: |
Sixteen types of Biso-coated designs, on ThO/sub 2/ kernels, were irradiated in High Flux Isotope Reactor target capsules HT-12 through HT-15. The report addresses the description of the experiment and extensive postirradiation analyses and experiments to determine fertile-particle burnup, fuel coating failures, and fission product behavior. Several low-temperature isotropic (LTI) pyrocarbon coatings, which ''survived'' according to visual inspection, were shown to have developed permeability during irradiation. These particles were irradiated at temperatures approximately equal to 1250/sup 0/C and to burnups equal to or greater than 8 percent fission per initial heavy-metal atom (FIMA). No evidence of permeability was found in similar particles irradiated at temperatures approximately equal to 1550/sup 0/C and burnups approximately equal to 16 percent FIMA. Failures due to permeability were not detectable by visual inspection but required a more extensive investigation by the 1000/sup 0/C gaseous chlorine leaching technique. Maximum particle surface operating temperatures were found to be approximately 300/sup 0/C in excess of design limits of 900/sup 0/C (low-temperature magazines) and 1250/sup 0/C (high-temperature magazines). The extremes of high temperatures and fast neutron fluences up to 1.6 x 10/sup 22/ neutrons/cm/sup 2/ produced severe degradation and swelling of the Poco graphite magazines and sample holders. |
