5- 4.1 Introduction

In the power-range channels, neutron-flux-measuring circuits monitor the neutron flux when the reactor is operating at or nea. full power. The channels provide information necessary for either manual or automatic control of the reactor

The power-range channels cover linearly one decade of power, thus providing a much finer control of power level than is possible with the logarithmic channels The system provides a linear display of power level over a wide range, the range being changed by switching

A power-range channel, shown in Fig 5 18, consists of a CIC, high-voltage supply, linear picoammeter, and readout and control signals Each of these items is discussed in the following paragraphs.

5- 4.2 Sensor

A CIC with the same characteristics as those used in the intermediate-level channel is used [see Sec. 5-3.2(a) and the discussion of CIC’s in Chap. 2, Sec 2-2 2].

5- 4.3 High-Voltage Supplies

See Sec 5-3.2(b).

5- 4.4 Linear Picoammeter

The signal from the CIC is monitored by a linear picoammeter with either manual or automatic range con­trol. In a manually operated unit, the current range is predetermined and normally provides an accurate indica­
tion of power level only for the highest two decades of power. Figure 5 19 shows an automatic range-changing picoammeter that gives continuous coverage from a few watts to full power The unit automatically changes range on an increasing and decreasing signal at the range set points

The basic current-measuring device of the picoammeter is an electrometer with appropriate feedback resistors to determine the range of operation. The electrometer, shown schematically m Fig 5.20, consists of a very high input impedance operational amplifier.

5- 4.5 Readout Indication

Signals generated from the picoammeter are presented to the operator in several ways The range is indicated by readout lamps, the level is displayed on meters and recorders marked 0 to 100% The level can also be displayed on a digital readout unit

5- 4.6 Control and Safety Circuits

Alarm units are provided in the picoammeter for initiating a. reactor shutdown if the power level exceeds a predetermined maximum value The alarm unit is described in Sec 5 2.4(e) The relays are connected in a two-out-of — three sequence to increase system reliability against single failures causing reactor shutdown (see Chap. 11)

5- 4.7 Calibration and Checkout

As with the other channels described in this chapter, a built-in test source is provided to check the system response from the picoammeter The test source also provides a means for setting and checking the alarm units



Fig. 5.19—Automatic range-changing picoammeter






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