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Unformatted text preview: a core, power cannot decrease any faster than the decay rate of the longest lived delayed neutron precursors. For 235U the mean lifetime of the longest lived precursors is about 80 s. Thus, the smallest asymptotic period for a very subcritical reactor is T = -80 s. Asymptotically, the power decays exponen-tially, i.e., P(t) = P(O) exp[tjT]. Solving this equation for t, and ignoring any prompt drop in power, the time to decrease the power to O.OOOlP(O) is Then from Eq. (10.16), which can be written as P(t) = P(O) exp[tjT], ( P(t) ) = (85 t=Tln P(O) = 785 s = 13.1 min. July 24, 2002 ( 166 W ) ;) In wow:...
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- Spring '06