Effective Cross Section of ~(238)U Samples for Analyzing Doppler Effect Measurements in Fast Critical Assembly

摘要

A new effective cross section of ~(238)U sample has been derived to accurately analyze the Doppler effect measurements in a fast critical assembly. The neutron spectrum in the sample is determined by considering the interference effect of neutron spectrum between the sample and the surrounding fuel region, and is used to obtain the effective cross section of the sample. The new effective cross section can be calculated using the conventional self-shielding factors. The use of the present cross section has increased the Doppler reactivity worth in ZPPR-9 by about 4% compared to the result calculated by the conventional self-shielding factor method without the spectrum interference effect. The physical meaning of this increment is discussed.