NUCE 402: Introduction to Nuclear System and Operation (PDF)

NUCE 402: Introduction to Nuclear System and Operation Chapter 4 (Plant Control) Dr. Ahmed Alkaabi  power Basic Plant Control Start up  load ms...

NUCE 402: Introduction to Nuclear System and Operation Chapter 4 (Plant Control) Dr. Ahmed Alkaabi  power Basic Plant Control Start up  load ms Plant control Scheme Shut down load Rx (QRX  Th) Turbine -(ms  Pimp) ms SG -(QSG  Tc) - Ps - Ts - ms Generator - load  power Basic Plant Control QSG ↑ = UA (Tprimary - Tsecondary ↓) constant Basic Control Scheme I :  to maintain a constant average reactor coolant temperature at all power Primary Secondary Th Tc Basic Plant Control Basic Control Scheme I : (load 0100%)  to maintain a constant average reactor coolant temperature at all power  main advantages minimize the size of the pressurizer through minimizing the variations of RCS water volume small reactivity variation due to small RCS temperature variation  main disadvantages large steam pressure variation -> large level variation in the steam generators and minimizing load at full power Basic Plant Control QSG ↑ = UA (Tprimary ↑ - Tsecondary ) constant Basic Control Scheme II :  to maintain a constant steam pressure at all power Primary Secondary Basic Plant Control Basic Control Scheme II :  to maintain a constant steam pressure at all power  Main advantages small steam pressure variation -> small level variation in the steam generators and maximizing load at full power  Main disadvantages maximize the size of the pressurizer and the requirement on CVCS through maximizing the variations of RCS water volume large reactivity variation due to large RCS temperature excursion Basic Plant Control Sliding Tavg Control Scheme :  Characteristics of a Sliding Average Temperature Program Basic Plant Control Sliding Tavg Control Scheme :  Reactor power is adjusted to maintain a programmed Tavg as turbine power is changed turbine-side control: the turbine governor valves are controlled by the error between the reference load and the actual load which is measured by the impulse pressure reactor-side control: the control rods are controlled by the errors between the reference Tavg and the actual Tavg the actual load is measured through the impulse pressure in the turbine  power Basic Plant Control Start up  load ms Plant control Scheme Shut down load Rx (QRX  Th) Turbine -(ms  Pimp) ms SG -(QSG  Tc) - Ps - Ts - ms Generator - load  power Fission Process and Criticality Negative feedback effect From Reactor concepts manual by USNRC Technical training center Practical Example #1 Plant control in case of more demand on load  More demand on load with automatic mode negative feedback without control rod movement – Qdemand (↑ )  pimpref (↑ )  ( + ) (pimpref - pimp)  ms (↑ ) Ps(↓ )  Ts (↓ )  QSG (↑ )  TCL (↓ )  Tavg (↓ )  ( + )ρreacivity  QRX (↑ )  Tavg (↑ ) QSG (↑ )  Ps (↑ )  ms (↑ ) QSG = UA SG (Tprimary - Tsecondary ) Practical Example #1 Plant control in case of more demand on load  More demand on load with automatic mode feedback control with control rod movement – feedforward control with control rod movement – Qdemand (↑ )  pimpref (↑ )  ( + ) (Tavgref - Tavg) control rod (↑ )  ( + )ρreacivity  QRX (↑ )  Tavg (↑ ) QSG (↑ )  Ps (↑ )  ms (↑ ) – long-term control rod movement: Xe oscillation QRX (↑ )  Xe (↓ )  ( + )ρreacivity after about two hours  control rod (↓ ) to maintain Tavg = Tavgref  ( - )ρreacivity  Xe (↑ ) after about four hours to build up to equilibrium value Practical Example #2 QSG = UA SG (Tprimary - Tsecondary ) Plant response in case of plugging of S/G tubes – U(↓ ) or A(↓ )  ps(↓ ) Ts (↓ )  pimp (↓ )  Athrottle (↑ )  the same Qload  QSG (↑ )  QRX (↑ ) When turbine and generator output stays the same and Tavg stays the same → reactor power and power through SG must increase → lowering thermal efficiency (higher reactor power but the same turbine power) As the number of the SG tubes plugged increases, the area of the turbine throttles increases. The turbine margin, usually 5-10%, is provided to accommodate the need of the more opening of the turbine throttles so that the turbine power may remain the same. Practical Example #3 Plant response in case of degradation of condenser tubes – Qcondenser = (UA) condenser (Tcondenser - Tcoolingwater ) – U(↓ ) or A(↓ )  pc(↑ ) Tc (↑ )  pimp (↑ )  Athrottle (↓ )  ms (↓ )  Qload (↓ ) ps(↑ )  QRX (↓ )  QSG (↓ ) When the turbine impulse pressure stays the same and maintaining the same Tavgref (no control rod movement )  lowering QSG and QRX due to higher Ps Turbine and generator output remains lower It can be a main cause of load degradation with reactor operating time Homework practice Plant control in case of less demand on load  less demand on load with automatic mode negative feedback without control rod movement – Qdemand (↓ )  pimpref ( )  ( ) (pimpref - pimp)  ms ( ) Ps( )  Ts ( )  QSG ( )  TCL ( )  Tavg ( )( )ρreacivity  QRX ( )  Tavg ( ) QSG ( )  Ps ( )  ms ( ) QSG = UA SG (Tprimary - Tsecondary )