Evaluation of delayed neutron data for JENDL-3.3

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