Measurement of keff with an improved neutron source multiplication method based on numerical analysis

In this work, we developed a numerical analysis-associated experiment method to determine the effective mul- tiplication factor heft, which is difficult to obtain directly from conventional neutron source multiplication （NSM） method. The method is based on the relationship between keff, subcritical multiplication factor ks and external neutron source efficiency in the subcritical system. On basis of the theoretical analysis, the dependence of ks and on subcriticality and source position was investigated at the Chinese Fast Burst Reactor-II （CFBR-Ⅱ）. A series of k were measured by NSM experiments at four subcritical states （ke= 0.996, 0.994, 0.991 and 0.986） with the 252Cf neutron source located at different positions （from the system center to outside） at each subcritical states. The φ＊ was obtained by Monte-Carlo simulation for each condition. With the measured k and calculated φ＊, keff of the subcritical system was evaluated with a relative difference of 〈 1% between values obtained by the improved method and by positive period method. Especially, the relative difference of 〈 0.18% with the source located at the system center.