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. LOSS OF POWER TO CONTROL ROD DRIVES Each of the 21 control rods has its own drive mounted vertically on the upper reactor head. Of these, 9 are servo controlled and 12 are of the nonservo type. The 9 servo rods have variable speed drives and operate in two groups in a synchronous manner, according to demand signals from the reactor system. The 12-rod group can be operated manually or in groups according to predetermined conditions. All of these operate at a speed determined by their gearing. The safety considerations are as follows: 1. Each servo loop contains a monitor that will sound an alarm and initiate a fast insertion if the rod fails to follow its command signal. 2. Another circuit monitors all nine servo monitors, and should any of the servo monitors malfunction, an alarm will sound and appropriate corrective action will be taken through the automatic safety system. 3. “Scram” action starts in the safety system and is independent of operator control. Once started, a “scram” action cannot be stopped. 4. For conditions that do not warrant “scram” action, a fast insertion serves to reduce power and permit the operator to correct the condition without a complete shutdown. A manual fast insertion can be made by the operator.