Steam Dumps

Question 1

STATE the four (4) functions of the steam dump system

Answer 1

• It prevents plant trips following limited load reduction by assisting the rod control system in returning Tavg to a program band.
• It returns Tavg to no-load value (557°F) following a plant trip without steam generator safety valve actuation.
• It creates an artificial steam load during turbine startup and shutdown to ensure smooth reactor load shifts.
• It provides a means of cooling down the reactor plant following reactor shutdown.

Question 2

DESCRIBE the two (2) modes of operation of the steam dump system.

Answer 2

• RCS Tavg Mode
• Utilized during power operation
• Steam Dump’s work in conjunction with Rod Control System to restore RCS Temperature to program value (Tref)
• Steam Pressure Mode
• Utilized during Plant startup and shutdown when Tavg is ≤0% plant power value of 557°F
• Steam Dumps are controlled to maintain Steam Generator pressure at setpoint pressure selected by the Operator
• Since S/G’s are at saturation, varying steam pressure directly varies RCS temperature.

Question 3

DESCRIBE how to locally operate a steam dump valve.

Answer 3

Manual handwheel on each steam dump for local operation. CAN ONLY BE OPENED WITH HANDWHEEL. For local closing of the valve, air to the actuator can be isolated to fail the valve closed.

Question 4

DESCRIBE why the condenser steam dump valves are arranged into four banks of valves.

Answer 4

Provides a gradual linear response for steam dump operation.