The A.C. Coupled Shut-down Amplifier as a Safety Device in Nuclear Power Stations

The shut-down amplifier supplies information to the safety circuits, so as to produce a reactor shut-down when the power exceeds a pre-determined level. A current, proportional to the reactor power, is obtained from a neutron sensitive ionization chamber. This current is compared with that obtained from a variable reference source whose output is calibrated in terms of equivalent reactor power. The shut-down amplifier gives a safe output only when the reactor power is below the reference setting. Any other condition, including fault conditions in the amplifier, must produce a trip signal. The two most essential design features of such an amplifier are absolute reliability of trip action in response to reactor power levels and low fault rate to minimize the number of spurious reactor shut-downs.