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Control Rod Drive System (PRD) Overview

● P. J. Sebastiani● University of Pittsburgh ME 2120● February 7, 2011

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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

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Control Rod Drive System (PRD)Purpose of the SystemReactivity 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

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Control Rod Drive System (PRD)BackgroundRod 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.

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

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Control Rod Drive System (PRD)Background (continued)RCCA Groups in the Core

NOTE: AP1000 will have a different rod pattern

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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)

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Control Rod Drive System (PRD)Required OutputsRods 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

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Control Rod Drive System (PRD)Initial ConditionsControl Scheme

– Automatic or Manual ControlRod 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

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Control Rod Drive System (PRD)Time-Dependent Boundary ConditionsCore Average Temperature (TAVG)

– Calculated using cold leg (TCOLD) and hot leg (THOT)

temperature values

– Input to the “Temperature Error” signalReactor 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)

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Control Rod Drive System (PRD)Time-Dependent Boundary Conditions (cont.)

Trip Breaker Setting– i.e., Manual Reactor Trip

– Open or Closed

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Control Rod Drive System (PRD)Required GeometryControl Rod Pattern

– See Background Section for example

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Control Rod Drive System (PRD)Pertinent PhysicsTotal Error Calculation

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Control Rod Drive System (PRD)Pertinent PhysicsRods Move Speed

Deadband

Inward Motion

Total Error (TRef - TAvg)

Outward MotionSpeed

72 spm

40 spm

8 spm

-5.0 -3.0 -1.5 0 +1.5 +3.0 +5.0 F

LockupLockup

º

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Control Rod Drive System (PRD)Viewable SignalsControl 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

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End of Presentation