Estimation of reactor core water level using gamma distribution measured at multiple axial points outside reactor in severe accident scenarios employing interacting multiple model

Highlights: • Gamma radiation is available irrespective of operating condition of reactor. • Measured gamma radiation outside reactor is affected by reactor core water level. • IMM with three model conditioned KF is used to estimate the axial radiation distribution. • Estimated radiation distribution is used to predict water level inside reactor core. • SA initiated by five cases are tested for Gamma radiation and water level estimation. The water level inside the core provides information about the reactor's safe operation. In severe accidents (SA), the water level information inside the reactor core may not be available as the conventional reactor devices for water level measurement are out of range. The gamma radiation collected from the detectors placed outside the reactor vessel is axially affected by the water level and fuel distribution present inside the core. This study predicts the water level in the core from the radiation distribution during events arising after the SA. An interacting multiple model (IMM) algorithm is used to determine the core water level by estimating the time-varying radiation distribution at multiple axial points. Numerical experiments using MELCOR code simulate the gamma radiation distribution in different SA scenarios. The results show that water level is estimated with reasonable accuracy using the proposed IMM method and helps diagnose and develop SA conditions measures.