Reactor Plant Control

1. Reactor Plant Control The Nuclear Gas Pedal

2. Topics To Cover • Components of Reactor • Reactor Core • Reactor Vessel • Supporting Components • Pressurizer (Pzr) • Reactor Coolant Pumps (RCP’s) • Steam Generators (S/G’s) • Shielding • Control of Reactor

3. Goal: Determine Functions

4. Primary Loop

5. Core Assembly • Fuel Assembly: stores, supports, and isolates fuel • Plate: UO2 clad with Zr metal; very thin to allow for effective heat transfer • Forms corrosion resistant layer to prevent corrosion by coolant

6. Core Assembly • Primary Coolant: removes heat produced by fission in fuel • Naval reactors use water (effective, easily replaceable, does not radiate) • Typical outlet temp ~ 500 oF • Typical inlet temp ~ 450 oF • Typical temp w/in core = ?

7. Pressure Vessel • Purpose: provides structural support for Rx core & directs flow of coolant thru core • Closure Head: removable cover on top of pressure vessel • Closure bolts hold down • Uses seal to prevent leakage • Houses Control Rods

8. Control Rods • Shutdown: with all rods lowered, Rx cannot go critical • Startup: lift control rods to reduce “leakage” until Rx is critical; continue to lift until temp of moderator reacts to rod height changes -> let moderator control power • SCRAM: quick shutdown of Rx; drop rods to bottom vice electronically lower (SuperCritical Reactor Ax Man)

9. Pressurizer (Pzr) • Purpose: maintains primary coolant in subcooled state (prevent boiling) and provides surge volume for power transients • Operates at saturation conditions to allow for steam space (NO other part of primary at saturation conditions) • Uses electric heaters/spray to maintain high temp & pressure

10. Pressurizer (Pzr) • If Pzr not used: • Boiling in reactor core reduces ability to remove heat (mass flow rate and heat capacity reduced) • Boiling in pumps causes cavitation -> loss of flow through core

11. Reactor Coolant Pumps (RCP) • RCP: circulates primary coolant through the core • Multiple RCP’s for redundancy

12. Steam Generator (S/G) • S/G: acts as heat sink for reactor and produces steam for MS system • Shell and tube heat exchanger • Moisture Separators • Non-nuclear side called the “Secondary”

13. Shielding • Serves two purposes: • Reduce radiation outside reactor compartment to protect personnel • Reduce radiation inside reactor compartment to protect instruments/equipment

14. Shielding • All contained within RC to minimize radiation: • Pressure Vessel & Core • Pressurizer (Pzr) • Reactor Coolant Pumps (RCP’s) • Steam Generators (S/G’s)

16. Reactor Plant Control • Core reactivity/power is inversely proportional to moderator temperature (negative temperature coefficient) • Operating AA1/3 -> AAIII Ordered • Open throttles -> Steam demand -> Tc • Tave -> density moderator -> greater chance neutrons will collide with H2O

17. Reactor Control • Higher prob. that neutron will thermalize and cause fission -> fission rate -> Rx power • Th -> Tave -> density moderator -> more chance of fast leakage • Lower prob. that neutron will thermalize -> fission rate -> reactor power • Tave returns to steady state

18. Reactor Control • Overall, REACTOR POWER FOLLOWS STEAM DEMAND • While Tave will remain roughly constant from steady-state to steady-state, Th and Tc will change depending on steam demand

19. Any Questions?