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

EO 3.5STATE the reason gamma compensation is NOT required in the power range.

EO 3.6Given a block diagram of a typical power range instrument, STATE the purpose of major components.

a. Linear amplifier

b. Reactor protection interface

Power range nuclear instrumentation normally consists of four identical linear power level channels which originate in eight uncompensated ion chambers. The output is a steady current produced by the neutron flux. Uncompensated ion chambers are utilized in the power range because gamma compensation is unnecessary; the neutron-to-gamma flux ratio is high. Having a high neutron-to-gamma flux ratio means that the number of gammas is insignificant compared to the number of neutrons.

The output of each power range channel is directly proportional to reactor power and typically covers a range from 0% to 125% of full power, but varies with each reactor. The output of each channel is displayed on a meter in terms of power level in percent of full rated power. The gain of each instrument is adjustable which provides a means for calibrating the output. This adjustment is normally determined by using a plant heat balance. Protective actions may be initiated by high power level on any two channels; this is termed coincidence operation.

Figure 37 shows a typical power range channel.

Figure 37 Power Range Channel

Two detectors in each channel are functionally connected in parallel so that the measured signal is the sum of the two detectors. This output drives a linear amplifier which amplifies the signal to a useful level.

The reactor protective interface provides signals for protective actions. Examples of protective action signals provided by the power range include:

A signal to the reactor protection system at a selected value (normally 10% reactor power) to disable the high startup rate reactor trip

A signal to protective systems when reactor power level exceeds predetermined values

A signal for use in the reactor control system

A signal to the power-to-flow circuit

Summary

Gamma compensation is NOT required in the power range since neutrons outnumber gammas by such a large number that gammas are insignificant. The purposes of power range components are summarized below.

Power Range Instrumentation Summary

The linear amplifier amplifies the signal to a useful level.

The reactor protective interface provides signals for protective actions.