CRD Mechanical Flashcards
What are the functions of groups 1 - 4? 5-7? APSRs?
Groups 1 - 4 are the safety groups and provide adequate S/D
Groups 5-7 are the regulating rods that are independently powered and provide a means of moving rods to achieve criticality and control power output in mode 1.
APSRs (axial power shaping rods) are partial length rods (63”) that are used for adjusting axial flux distribution.
What is the purpose of the ball check valves equipped on the CRDs?
The ball check valves are at the base of the thermal barrier to permit flow into the void created when the rod drops on reactor trip. APSRs are not equipped with the ball check valve.
What are the control rods made of and what length is the poison absorption?
AgInCd (Silver,Indium,Cadmium) -> Neutron absorber
Poison absorption length is 139”
What are the 2 different speeds that the control rods are operated in?
- Run Speed - operate at 30”/min
- Jog Speed - operate at 3”/min
What prevents the APSRs from inserting on a reactor trip?
APSRs are mechanically held by contact buttons on the bottom of the segment arms to prevent insertion when de-energized
What is the thermal barrier of a control rod and what is its function?
Thermal barrier restricts circulation of the primary coolant and acts as an insulator to prevent rod from getting too hot. It limits temperature to 300-350 degrees F and houses the ball check valves.
What is the purpose of the synchronizing bearing?
The sync bearing is positioned on the upper portion of the rotor assembly and ensure both segment arms move together
Describe the segment arms and roller nuts and means by which a control rod remains engaged?
The segment arms are magnetically powered to engage the segment arms, overcoming spring pressure. When the CRD is energized the segment arms engage the roller nuts (4 per rod) and allow movement of the control rod. Once the rod is de-energized by a RX trip, the segment arms are no longer magnetically held and the spring pressure disengages the segment arms from the roller nuts and allows the rod to drop.
What prevents outward travel of a control rod and prevents it from contacting the top closure assembly? What would happen if this feature failed?
The first rod which reaches its out limit stops rod movement of the group. If this feature were to fail, it would contact the top closure assembly and cause the motor to skip poles of the torque tube.
What prevents rotation of the lead screw and allows only up and down motion?
The torque taker is keyed to the torque tube.
What absorbs the shock of the lead screw dropping by narrowing of the tube? What device absorbs the remaining energy near end of the stroke?
The buffer (snubber) assembly design limits the shock initially and belleville washers absorb the remaining energy.
What provides API indication and where are the magnets mounted? RPI?
API indication is generated from a 4” magnet mounted to the torque taker using 79 reed switches housed in a fiberglass housing along the rod.
RPI indication is generated from a stepping motor that operates a rheostat. RPI indication can be read on the PI Panel or PDS.
How much ICW flow is there through the stator water jacket?
2 gpm of ICW flow cools the 6 phase, 4 pole stepping motor which keeps temperature < 120 degrees F.
What are the CRD temperature limitations?
Max stator temperature requiring de-energizing CRDM is 180 degrees F.
Max temp of cooling water entering CRD is 120 degrees F.
Min cooling water temp is 60 degrees F
Min allowable RC temperature for ICW to be aligned to de-energized CRD stators is 200 degrees F.
