Control Rod Drive System (PRD) Overview

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