Use of Campbell´s Method in Nuclear Reactor Control Instrumentation

The measurement of statistical fluctuations from neutron detectors yield an information proportional to the root mean square of the flux which is used in reactor control. The theory shows that neutron-gamma discrimination is improved by a factor 100 relative to a current measurement, when an uncompensated ionization chamber is used. Another advantage of this method is to have the possibility to connect on the same detector two measuring channels (logarithmic and linear channel for instance). An experimental logarithmic amplifier has been realized upon this principle. It operates over a three decade range (six decade flux range). Experimental results of measurements done on high flux experimental reactor are given.