Investigations of sample reactivity worth measurement in a fast neutron reactor with the inverse kinetics method

A new method for the measurement of sample reactivity worth in a fast neutron reactor named the inverse kinetics method is proposed in the paper. The sample reactivity worth could be obtained by measuring the reactivity step change in the process of sample fetching and placing in the delayed critical reactor. Compared with the traditional period method, the advantage is that the accuracy of reactor reactivity control will not exert any influence on the uncertainty of reactivity worth measurement. The inverse kinetics method has been used to measure the reactivity worth of Ф20 mm × 9 mm Au, V and Be samples at the center of the upper surface of a highly enriched uranium fast neutron reactor, and the results are 5.17¢, 4.40¢ and 5.90¢ respectively, which are consistent with those obtained with the period method. The standard uncertainty of measurement of the results is about 0.03¢, which achieves an obvious improvement compared with that (∼0.08¢) of the period method.