REACTOR CONTROL AND SAFETY SYSTEMS The design of the control system is such that a malfunction which leads to an abnormal withdrawal rate of the rods will not result in a dangerous condition. Studies indicate that the minimum reactor period resulting from maximum withdrawal of the rods is not less than 30 seconds. The control system is designed to maintain the _net_ reactivity insertion always less than the delayed neutron fraction. The entire reactor system is protected by the safety system. This system causes the reactor to terminate power production if a dangerous operating condition exists. The safety system also contains interlocks which prevent actions which would otherwise jeopardize the reactor system. The control and safety systems are capable of protecting the reactor system from damage due to any credible accident except a major leak in the primary loop. The reactor will “scram” (shut down) automatically from any of seven causes: (1) shorter than a safe reactor period, (2) excessive power, (3) excessive rise or fall in reactor pressure, (4) excessive reactor outlet pressure, (5) loss of flow, (6) loss of power to safety circuits, and (7) loss of power to control rod drives. INSTRUMENTS DOUBLE CHECKED The nuclear instrumentation system provides maximum reliability and safety, yet minimizes erroneous readings or signals from the monitoring channels. This is done by using two or more measuring channels in each operating range, and then interlocking the circuits so that at least two of them give the same signal of abnormal operating conditions before initiating a reactor “scram.” Increased reliability is obtained by using “solid state” instruments or magnetic amplifier units rather than electron tubes and relays. REACTOR SAFETY SYSTEM This system constantly monitors signals from the nuclear and non-nuclear instrumentation, and when necessary takes corrective action. Corrective action will be either in the form of “fast insertion” of the control rods, or in the form of reactor “scram.” Fast insertion takes place at a rate of 15 inches per minute, while a scram is achieved in 1.6 seconds. Fast insertion consists of moving all control rods to the full down position at the fastest rate possible through the electromechanical drives. For reactor “scram,” all rods are driven to full down position under the force of a net hydraulic pressure of 1,250 psi. SHORTER THAN A SAFE PERIOD The reactor period is a measure of the rate of reactor power increase; the shorter the period the faster the rise. Ten neutron-measuring channels, covering the full range from source level to 150 percent of maximum power, measure neutron intensity (flux level) and its rate of change. These data are continuously transmitted to the reactor operator and the automatic control and safety system. Too fast a rate of change, or shorter than a safe period, will automatically “scram” the reactor. EXCESSIVE POWER