Numerical simulator for noise diagnostic investigations in NPPs

A coupled thermohydraulics and neutron model is used to simulate signals of thermocouples, ex-core and in-core neutron detectors of nuclear power plan ts (NPP). Noise sources are generated as time functions and the dynamic beh avior of the reactor core is modeled by one-dimensional two-group diffusion equations coupled with an axial thermohydraulics model. These equations ar e solved by numerical methods and the resulting time series are considered as virtual measurements. We show that one can model only a finite set of no ise sources with high accuracy by this approach because of the finite natur e of numerical methods. The selection of length of space segments is presen ted and the effect of space aliasing is briefly discussed. An automatic ste psize selection algorithm is introduced which was applied successfully in t he simulator. Simulation results are analyzed and compared with real measur ements by studying disturbance propagation in the coolant. (C) 1998 Elsevie r Science Ltd. All rights reserved.