Interpretation of the central cell reactivity worth and experimental determination of a characteristic value of the reactor cell composition Ksub(m)+

It has been made clear that the reactivity worth of the central cell may be considered equal to the worth of the leakage neutrons from the cell. Thus, the value may be used to evaluate the results of neutron leakage calculations. A method is proposed for the experimental determination of km +, a characteristic value of the reactor cell composition, by making use of the reactivity worth of the cell measured at the core center. The quantity km + is a kind of infinite multiplication factor defined in the fundamental mode spectra. Since accurate methods based on the fine group treatment are available for calculating km +, its measurement is valuable for evaluating the cross section library used for reactor calculations. As an example, the value of km + has been obtained for the FCA Assembly V-2, and the resulting experimental and calculated values are examined.