The amount of power produced is a function of the neutron flux and its resultant heat generation in the primary loop. The temperature selected to produce automatic “scram” is 540° F. This temperature “scram” circuit provides an independent backup to the neutron flux “scram.”
EXCESSIVE RISE OR FALL IN PRESSURE
Too low a pressure could result in boiling of the primary coolant, while too high a pressure could result in poor heat transfer as well as placing unnecessary stresses on the reactor’s fuel element core structure. There are a number of causes for either condition, all of which would relay a “scram” signal to the operator and to the automatic safety system.
EXCESSIVE OUTLET PRESSURE
In addition to protection against rapid rate of change in pressure, a scram circuit is provided to prevent any steady excessive outlet pressure that could result in damage to the core and related equipment.
LOSS OF FLOW
This condition would result from a mechanical failure in the primary loop pumps, piping, etc., or by accidentally stopping the pumps when the reactor is at power, or by loss of power to the pumps. When a single pump fails to operate for any reason, an alarm is sounded to warn the operator. If all four pumps fail to operate for any reason, a signal is sent to the reactor safety system to “scram” the reactor.
LOSS OF POWER TO SAFETY CIRCUITS
The hydraulic drives that operate the “scram” mechanism require reserve pressure to keep them in the “ready” position for “scram” condition and are an integral part of the safety circuitry. A power failure in the safety circuits would automatically put the hydraulic drives into operation to “scram” the reactor.