Unformatted text preview: Solution: For a given material, koo is fixed, and the geometry affects only the nonleakage probabilities ~~ and P~. These nonleakage probabilities both increase as the critical buckling Bc decreases. For a given volume, B; is smallest for a sphere (see Table 10.6). Thus, a sphere has the smallest critical mass. Alternatiely, for a given volume, a sphere has the smallest surface area and hence the least amount of neutron leakage. Thus, if the sphere is critical, any other shape must have a greater volume (mass) of material to be critical. 10. If the uranium fuel enrichment in a reactor is increased, what is the effect on koo? Explain. Solution: As the uranium enrichment increases, only the thermal fission factor 1/ is affected. The thermal fission factor is As the enrichment increases, the ratio N238/ N235 decreases, 11 increase, and koo increases. July 24, 2002...
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 Spring '06
 CADY
 Fundamental physics concepts, Nuclear weapon, Koo, Plutonium239, Nuclear weapon design

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