CRITICAL STUDIES OF A FAST REACTOR CORE CONTAINING DEPLETED URANIUM AND SODIUM AS DILUENTS. (APR-III Assembly 36)

Critical studies were performed with a metallic, fast reactor core designed to snvestigate the effects of replacing highly absorbing U/sup 238/ diluent with high-scattering, lowabsorbing sodium diluent. The fuel was 15.7 wt% enriched U/sup 235/ and the core contained 18.2 vol% sodium and 12.68 vol% stainless steel. The experimental program was designed to measure the effect of the material replacement on spectral indices, which consisted of the standard fission ratios, foil irradiations, and a large number of central reactivity coefficients. Other measurements included the Rossi- alpha , radial fission traverses, and edge reactivity worths of a few samples. (auth

Advanced Methods Comparisons of Reaction Rates in the Purdue Fast Breeder Blanket Facility

A review of worldwide results revealed that reaction rates in the blanket region are generally underpredicted with the discrepancy increasing with penetration; however, these results vary widely. Experiments in the large uniform Purdue Fast Breeder Blanket Facility (FBBF) blanket yield an accurate quantification of this discrepancy. Using standard production code methods (diffusion theory with 50 group cross sections), a consistent Calculated/Experimental (C/E) drop-off was observed for various reaction rates. A 50% increase in the calculated results at the outer edge of the blanket is necessary for agreement with experiments. The usefulness of refined group constant generation utilizing specialized weighting spectra and transport theory methods in correcting this discrepancy was analyzed. Refined group constants reduce the discrepancy to half that observed using the standard method. The surprising result was that transport methods had no effect on the blanket deviations; thus, transport theory considerations do not constitute or even contribute to an explanation of the blanket discrepancies. The residual blanket C/E drop-off (about half the standard drop-off) using advanced methods must be caused by some approximations which are applied in all current methods. 27 refs., 3 figs., 1 tab