Dynamic Rod Worth Estimation with Extended Kalman Filter and Background Current Elimination

The dynamical rod worth method (DRWM) is a fast and accurate method to measure and validate the worth of control rod during the zero power physics test at pressure water nuclear reactors. The control rod worth is obtained from the reactivity change caused by the fast insertion of the control rod into the bottom of the core. The reactivity is calculated based the measured ex-core detector signals which normally varies from ~ 10²nA to ~ 10⁰nA during the rod insertion process. During the later stage of the test, as the detector signal becomes ~ 10⁰nA, the impact of the measurement noise and the gamma-ray background current on the reactivity calculation becomes significant. In this paper, we developed an extended Kalman filter (EKF) with suitable weighing matrices to filter out the measurement noise. With most measurement noise filtered out, a background current estimation method is used to eliminate the effect of the background current. By combining the background current estimation method with EKF filter, accurate control rod worth is obtained from the real test data.