1. Control Rod Drive System (PRD) Overview
P. J. Sebastiani
University of Pittsburgh ME 2120
February 7, 2011

2. Control Rod Drive System (PRD) Agenda
Purpose of the System
Background
Required Outputs
Initial Conditions
Time-Dependent Boundary Conditions
Required Geometry
Pertinent Physics
Viewable Signals

3. Control Rod Drive System (PRD) Purpose of the System
Reactivity Control
The reactor core utilizes Rod Cluster Control Assemblies which provide reactivity control for:
Rapid shutdown (i.e., reactor trip)
Reactivity changes due to temperature changes with power (i.e., power defect)
Reactivity changes due to coolant temperature changes in the power range (i.e., moderator temperature feedback)
Reactivity changes due to void formation

4. Control Rod Drive System (PRD) Background
Rod Cluster Control Assemblies (RCCAs)
RCCAs consists of absorber rods attached to a spider connector which, in turn, is connected to a drive shaft.
RCCA control elements consist of cylindrical neutron absorber rods (control rods).
The control rods extend the full length of the core when fully inserted.
The RCCAs are arranged into groups and electrically interconnected so that the entire group moves together.
Reactivity of the core is changed by raising or lowering a group within the core.

5. Control Rod Drive System (PRD) Background (continued)
RCCA Diagram (within Fuel Assembly)

6. Control Rod Drive System (PRD) Background (continued)
RCCA Groups in the Core
NOTE: AP1000 will have a different rod pattern

7. Control Rod Drive System (PRD) Background (continued)
Control Rod Drive Mechanism
The RCCAs are positioned by latch-type magnetic jack control rod drive mechanisms (CRDMs) mounted on the reactor vessel head
Used to raise and lower the RCCAs (in/out of core)
Instantly releases RCCAs when necessary for rapid reactor shutdown (i.e., Reactor Trip)
Latch positions are referred to as “steps”
Stepping distance: 5/8 inch (in)
Total rod position indication length: ~230 steps (~144 in)
Maximum Rods Move Speed: 45 inch/min (72 steps/min)

8. Control Rod Drive System (PRD) Required Outputs
Rods Move Speed
Manual Control (default setting): 48 steps/min
Automatic Control: up to 72 steps/min (see Pertinent Physics Section)
Rods Move Direction
In or Out

9. Control Rod Drive System (PRD) Initial Conditions
Control Scheme
Automatic or Manual Control
Rod Insertion Limits
Technical Specification Limits on rod position to ensure adequate Shutdown Margin for the core
Rod Position
The current rod position at the start of the simulation

10. Control Rod Drive System (PRD) Time-Dependent Boundary Conditions
Core Average Temperature (TAVG)
Calculated using cold leg (TCOLD) and hot leg (THOT) temperature values
Input to the “Temperature Error” signal
Reactor Power (2 separate inputs)
One input from Turbine Impulse Pressure (for Temperature Error calculation)
Will this be available in PANTHER model?
One input from Power Range Detector (for Power Mismatch calculation)

11. Control Rod Drive System (PRD) Time-Dependent Boundary Conditions (cont.)
Trip Breaker Setting
i.e., Manual Reactor Trip
Open or Closed

12. Control Rod Drive System (PRD) Required Geometry
Control Rod Pattern
See Background Section for example

13. Control Rod Drive System (PRD) Pertinent Physics
Total Error Calculation

14. Control Rod Drive System (PRD) Pertinent Physics
Rods Move Speed

15. Control Rod Drive System (PRD) Viewable Signals
Control Scheme Selection
AUTO or MANUAL
Rod Position (steps withdrawn)
Rod Speed (steps/min)
Total Error
Rods Move Indication
Lamp for moving or not moving
“Clicking” noise during rod movement

16. End of Presentation