Experimental Studies of Core Flow Fluctuations as Noise Source in BWR

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 II 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 IFA 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...