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A Criticality Study of Fissile-Metal and Fissile-Solution Combinations

D. C. Hunt, Robert E. Rothe

Nuclear Science and Engineering

Volume 53 / Number 1 / January 1974 / Pages 79-92


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In evaluating fissile-material recovery operations involving metal salvage immersed in a reagent, a criticality safety engineer must be able to identify systems of minimum critical mass. Further, he must know the effect on the reproduction factor caused by changes in process variables such as container size or the fissile concentration of the reagent. This paper reports no new experimental results but studies the criticality aspects of fissile-metal immersion by analyzing the most applicable of the existing measurements. The results are expressed in terms of the critical mass of the metal region (excluding the mass of fissile material in solution) as a function of the fissile concentration and dimensions of the liquid cylinder., The analysis indicates that the critical mass of practical combinations of uranium metal and uranium solution always exceeds that of an 18.7-g/cm3, 93.2% 235U-enriched uranium sphere centered in a 300-g/liter metal-water mixture. The corresponding conservative approximation for plutonium systems holds for a 19.7-g/cm3, 95% 239Pu sphere in a 200-g/liter metal-water mixture. The upper limit of applicability of these results is 500 g/liter for both plutonium and uranium systems. The calculational techniques described in this paper underestimate critical masses of uranium by ∼5%; the calculated masses of plutonium are sufficiently overestimated to be conservative in practical applications.

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