Intermediate-range nuclear instrumentation consists of a minimum of two redundant channels. Each of these channels is made up of a boron-lined or boron gas-filled compensated ion chamber and associated signal measuring equipment of which the output is a steady current produced by the neutron flux.
The compensated ion chamber is utilized in the intermediate range because the current output is proportional to the relatively stable neutron flux, and it compensates for signals from gamma flux. This range of indication also provides a measure of the rate of change of neutron level. This rate of change is displayed on meters in terms of startup rate in decades per minute (-1 to +10 decades per minute). High startup rate on either channel may initiate a protective action. This protective action may be in the form of a control rod withdrawal inhibit and alarm, or a high startup rate reactor trip.
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