Automatic shutdown controller for nuclear reactor system with control drums

A nuclear reactor system, comprising:

• a pressure vessel;
• a nuclear reactor core disposed in the pressure vessel, the nuclear reactor core including a plurality of fuel elements and at least one moderator element;
• a plurality of control drums disposed longitudinally within the pressure vessel and laterally surrounding the plurality of fuel elements and the at least one moderator element to control reactivity of the nuclear reactor core, wherein each of the control drums includes a reflector material on a first portion of an outer surface and an absorber material on a second portion of the outer surface;
• an automatic shutdown controller including:
• a counterweight that is internal to a control drum of the plurality of control drums to impart a bias on the control drum,
• an actuator coupled to the counterweight,
• a guide ramp that opposes a lower end of the control drum and includes a guide surface, and
• a control drum reciprocal surface that extends from the lower end of the control drum;
• and
• an electrical drive mechanism that is:
• (a) powered by electrical power from a power source, (b) coupled to rotatably control the control drum, and (c) further coupled to the actuator, wherein:
• both the electrical drive mechanism and the actuator counteract the bias of the counterweight during availability of the electrical power from the power source, and
• during a loss or interruption of the electrical power from the power source such that the electrical power is no longer available to the electrical drive mechanism and the actuator, the guide surface is responsive to the bias of the counterweight and the control drum reciprocal surface to rotatably control the control drum to align the absorber material to face inwards towards the nuclear reactor core.