Radiation Detectors
SOURCE RANGE NUCLEAR INSTRUMENTATION
SOURCE RANGE NUCLEAR INSTRUMENTATION
Three ranges are used to monitor the power level of a reactor throughout the full
range of reactor operation. The source range makes use of a proportional
counter.
EO 3.3
Given a block diagram of a typical source range
instrument, STATE the purpose of major components.
a.
Linear amplifier
b.
Discriminator
c.
Pulse integrator
d.
Log count rate amplifier
e.
Differentiator
Source range instrumentation normally consists of two redundant count rate channels, each
composed of a high-sensitivity proportional counter and associated signal measuring equipment.
These channels are typically used over a counting range of 0.1 to 106 counts per second, but vary
based on reactor design. Their outputs are displayed on meters in terms of the logarithm of the
count rate.
Source range instrumentation also measures the rate of change of the count rate. The rate of
change is displayed on meters in terms of the startup rate from -1 to +10 decades per minute.
Protective functions are not normally associated with source range instrumentation because of
inherent limitations in this range. However, interlocks may be incorporated.
Many reactor plants have found it necessary to place source range proportional counters in lead
shielding to reduce gamma flux at the detectors. This serves two functions: (a) it increases the
low end sensitivity of the detector, and (b) it adds to detector life. Another means by which
detector life is extended is to disable the high voltage power supply to the detector and short the
signal lead when neutron flux has passed into the intermediate range. There are some reactor
plants that have made provisions for moving the source range detectors from their operating
positions to a position of reduced neutron flux level, once the flux level increases above the
source range.
Rev. 0
Page 63
IC-06
