Three ranges are used to monitor the power level of a reactor throughout the full range of reactor operation. The intermediate range makes use of a compensated ion chamber.

EO 3.4Given a block diagram of a typical intermediate range instrument, STATE the purpose of major components.

a. Log n amplifier

b. Differentiator

c. Reactor protection interface

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.

Figure 36 shows a typical intermediate-range channel.

Compensated Ion Chamber

Figure 36 Intermediate Range Channel

Typically, the compensated ion chamber output is an analog current ranging from 10^-11 to 10^-3 amperes, but varies with reactor design. The log n amplifier is a logarithmic current amplifier that converts the detector output to a signal proportional to the logarithm of the detector current. This logarithmic output is proportional to the logarithm of the neutron level.

The determination of rate change of the logarithm of the neutron level, as in the source range, is accomplished by the differentiator. The differentiator measures reactor period or startup rate. Startup rate in the intermediate range is more stable because the neutron level signal is subject to less sudden large variations. For this reason, intermediate-range startup rate is often used as an input to the reactor protection system.

The reactor protective interface provides signals for protective actions. Examples of protective actions include control rod withdrawal interlocks and startup rate reactor trips.

Summary

The purposes of intermediate range components are summarized below.

Intermediate Range Instrumentation Summary

The log n amplifier converts the detector output signal to a signal proportional to the logarithm of the detector current.

The differentiator provides an output proportional to the rate of change of power.

The reactor protection interface provides signals for protective actions.