Monitoring and analysis of nuclear power plant signals based on nonlinear dynamical methodology

The spatial correlation of a trajectory in the state space drawn by a dynamical system gives the information (fractal) dimension of the system, and enables the onset of the limit-cycle (or persistent) oscillation to be examined. On-line monitoring system with this methodology was established for a PWR-type nuclear power plant (NPP). The potential use of this methodology in monitoring NPP was tested from two actual situations in which anomaly developed. The spatial correlations of various NPP signals under normal operating conditions were calculated, yielding information unobtainable by conventional linear methodology. For example, results indicated that the coolant pump vibration was not linearly stabilized, that is, it was a limit-cycle oscillation. Swelling oscillation in the pressurizer pressure was also discovered by this methodology. (author)