A simple nonlinear model for pendular chaotic oscillations of reactor corebarrel

We propose a non-linear model reproducing the unidirectional (quasi)pendula r motion of pressurized water reactor (PWR) core barrel (CB), which is in i ntermittent contact with reactor pressure vessel (RPV) in places of lower f astenings. 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, ther e exists a possibility of chaotic pendular oscillations in the certain regi on of three parameters, namely, (i) the pendular oscillation frequency, (ii ) the resulting force acting on the CB at the main circulation pump (MCP) f requency from the coolant flows of opposite legs, and (iii) the clearance b etween the CB and RPV. Vibratory monitoring, which is realized in modem dia gnostic systems, in principle, allows one to distinguish between regular an d 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 s tabilizing chaotic oscillations by applying recently proposed control techn ique. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.