A correlator for investigating random fluctuations in nuclear power reactors

In nominally steady operation of a nuclear power reactor small fluctuations are observed in various parameters, e.g. reactor power, coolant flow and temperature. The cross-correlation between simultaneous recordings of these fluctuations can give information on the kinetics of the reactor system without disturbing its normal operation. An apparatus has been built to explore the practical possibilities of the technique and this paper describes its design principles, practical implementation and the results of tests. Some typical results obtained on the Dounreay Fast Reactor are also given. The equipment records the fluctuations in four channels on magnetic tape, the correlation functions being obtained subsequently by analogue computing techniques in an accelerated time scale. A novel feature is the use of a continuously-rotating magnetic drum with multiple heads to delay one signal relative to another. Delays equivalent to 25 seconds in recording time can be obtained, the smallest delay being 0.05 second. Tests with sinusoidal signals show that frequencies can be measured to better than 2% and the r.m.s. error of all points on the correlation curve is less than 2% of full scale. These errors are shown to be considerably less than the statistical errors due to the finite recording time.