Figure 21 Typical Compensation Curve

COMPENSATED ION CHAMBER Radiation Detectors The ionization chamber compensation Figure 21 Typical Compensation Curve curve, Figure 21, is a plot of the percent compensation versus compensating voltage. This compensation curve must be plotted prior to using a compensated ion chamber. In ideal situations, compensated ion chambers operate at 100% compensation, and indicated current is due to neutrons. Small changes in compensating voltage change the percent compensation. The consequences of operating with an overcompensated or undercompensated chamber are important. The purpose of nuclear instrumentation is to detect and measure neutron level, which is the direct measure of core power. If the compensating voltage is set too high, or overcompensated, some neutron current, as well as all of the gamma current, is blocked, and indicated power is lower than actual core power. If compensating voltage is set too low, or undercompensated, not all of the gamma current is blocked, and indicated power is higher than actual core power. At high power, gamma flux is relatively small compared to neutron flux, and the effects of improper compensation may not be noticed. It is extremely important, however, that the chamber be properly compensated during reactor startup and shutdown. IC-06 Page 38 Rev. 0