A simple nonlinear model for pendular chaotic oscillations of reactor core barrel

We propose a non-linear model reproducing the unidirectional (quasi)pendular motion of pressurized water reactor (PWR) core barrel (CB), which is in intermittent contact with reactor pressure vessel (RPV) in places of lower fastenings. Analytic formulae are obtained, which allow one to elucidate the influence of reactor parameters on the character of motion. We show by the example of the WWER-1000 reactor that, in the framework of our model, there exists a possibility of chaotic pendular oscillations in the certain region of three parameters, namely, (i) the pendular oscillation frequency, (ii) the resulting force acting on the CB at the main circulation pump (MCP) frequency from the coolant flows of opposite legs, and (iii) the clearance between the CB and RPV. Vibratory monitoring, which is realized in modem diagnostic systems, in principle, allows one to distinguish between regular and chaotic regimes, thus giving information about the state of fastenings in the lower part of the CB and RPV. We also demonstrate the possibility of stabilizing chaotic oscillations by applying recently proposed control technique. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.