Abstract
Among various fluctuating quantities in a BWR plant the present authors dealt with core channel flow fluctuations. Using the instrumented fuel assemblies (IFA) installed in the Japan Power Demonstration Reactor IC core, fluctuations of the inlet and outlet channel flow rates were observed at power operation condition. Correlation analyses of the fluctuating signals revealed the followings : (a) the flow fluctuations in any WA channel showed almost uncorrelated cross-correlation with other IFA channel flow, (b) cross-correlation between the neutron density fluctuations and each IFA channel flow fluctuations also showed little correlation, and (c) the forced circulation pump flow showed unexpectedly weak correlation with the core channel flow.
To attempt to explain the above facts, some hypotheses are introduced : (1) Each channel will be actuated by an independent weak noise source. (2) The fluctuating flow of a channel will interfere with each other, then the interferences will spread to the whole core and balance in a stationary state forming a certain statistical pattern. A dynamic equation of the channel flow fluctuations is introduced based on the above hypotheses, and the covariance functions of inter-channel flow fluctuations are calculated. The hypotheses are discussed by comparing with the results of identification by the use of an autoregressive model.
