Reactivity estimation based on the linear equation of characteristic time profile of power in subcritical quasi-steady state

The reactivity was estimated from a time profile of neutron count rate or simulated data in a quasi-steady state (QSS) after a sudden status change of reactivity or external neutron source strength. The estimation was based on the equation of power in subcritical QSS. The purpose of the study is to develop the method of timely reactivity estimation from complicated time profile of neutron count rate. The developed method was applied to the data simulating neutron count rate created by using one-point kinetics code, AGNES, and Poisson-distributed random noise. It was also applied to the transient subcritical experiment data measured by using transient experiment criticality facility. The result shows that the difference of the estimated and reference values was within about 5% or less for rho(s) > -10 for simulated data and within about 7% or less for rho(s) similar or equal to 1.4 and -3.1 for the experimental data. The possibility of the reactivity estimation several 10 seconds after the status change was also shown. [GRAPHICS] .