Delayed neutron data of 235U, 238U and 239Pu have been evaluated and recommended for JENDL-3.3. Adjustment of Vd was carried out on the basis of the ßeff measurements at FCA, MASURCA and TCA using the JENDL-3.2 data as the initial guess. Through this adjustment the vd value for 238U below 3.5 MeV was decreased by about 3% from 0.0481 to 0.0466. The vd values of 235U and 239Pu were also determined in this way. Further appropriate six group constants, the decay constants A¿ and the group yields αi, were determined from experimental data of the delayed neutron emission rates, which were collected and compiled by Spriggs through the SG6 activity of WPEC. Applicability of the resultant group constants was validated through the analyses of the reactivity measurements based on the period or the rod-drop methods.
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