Examination of applicability of IK method in the negative reactivity measurements

An alternative analysis procedure of the inverse kinetic method was applied to measurements of large negative reactivity in a subcritical fast reactor and its applicability was examined in comparison with conventional ones. The measurements were carried out in the rod-drop experiment with an external neutron source at a fast critical assembly FCA in JAERI. The negative reactivity in this experiment was supplied with control rod drops by about 6 $. It was found that the results of the conventional analysis procedures depend on their regression models when a count rate of neutron detector is small, and their experimental errors are somewhat unknown. The new analysis procedure based on the maximum-likelihood method can be successfully applied in a wide range of counting statistics and it is also useful to check the validity of the conventional procedures. (author)