Examination of Actual Neutron Count Rate Data during a Control Rod Drop Testing for Estimation of Control Rod Worth in PWRs

The Modified Neutron Source Multiplication (MNSM) method, which is based on the extraction of the fundamental mode of neutron flux distribution, has been proposed to estimate subcriticality. It has been proven applicable to a small critical assembly and domestic PWRs during criticality approach. In the following study, it is also shown by numerical simulation that it is applicable to estimate the subcriticality using neutron count rate data during the control rod drop testing in PWRs. As the next step, we looked further into the actual data of neutron count rate in order to examine whether the expected signal response was observed for the estimation. It was found that the actual data have shown the expected response, and the control rod worth could have been estimated in the same manner as during criticality approach. A new procedure is also proposed to measure a reference reactivity that is essentially required to evaluate the reactivity of each control rod worth.