Subcriticality estimation by extended Kalman filter technique in transient experiment with external neutron source at Kyoto University Critical Assembly

Abstract

The monitoring subcriticality by the extended Kalman filter (EKF) is evaluated in the presence of an external neutron source through transient analyses and compares with that by inverse kinetic method at Kyoto University Critical Assembly. Throughout the transient experiment, subcriticality is deduced with the use of neutron counts measured every 1 s. For ensuring the initial condition of the EKF technique, the basic transient experiment is carried out by dropping a control rod into the core at a critical state, and the result by the EKF technique shows remarkably accurate subcriticality as compared with the reference value obtained by the rod drop method with less fluctuation than by the inverse kinetic method. In the ADS transient experiment with the 14 MeV stable neutron source, the subcriticality is set as target subcriticality of the accelerator-driven system ($$k_\mathrm{eff}= 0.97$$); the external neutrons are then injected from outside the core. The EKF technique reveals significantly good agreement with MCNP6.1, whereas subcriticality by the inverse kinetic method fluctuates widely during the transient experiment. Thus transient experiment shows that the EKF technique is applicable to subcriticality monitoring with a high time resolution and a high degree of precision.