Extraction Steam and Heater Drains

Question 1

Where does the shell side and tube side of the MSR’s drain?

Answer 1

Shell Side

• This is the exhause of the HP Turbine. It is dried and re-heated in the MSR before entering the LP turbines.
• Condensate from the shell side drians to T-5, MSR Drain Tank.

Tube Side

• This is HP steam off the the main steam line. It used to heat the shell side steam. Makes 4 passes then flows to T-4A/B, Reheater Drain Tanks.

Question 2

Where do the high pressure feedwater heaters get heating from?

Answer 2

E-6A/B

• Third stage HP turbine exhaust
• T-4A/B Reheater Drain Tanks

E-5A/B

• E-6A/B Drains
• HP Turbine Exhaust Cross Under Drains (East Side Cross Under Only)

Question 3

What is the purpose of a Bleeder Trip Valve?

Answer 3

On turbine trip, it closes to prevent the steam in the feedwater heaters from rushing backing into the turbine and causing an overspeed.

Closes on high level in feedwater heater

BTVs are on lines feeding:

• E-6A/B
• E-4A/B
• E-3A/B

Question 4

How are the drains “cascade” in the High Pressure Feedwater Heater System?

Answer 4

Condensed extraction steam and drains from tanks T-4A/B are drained from the 6A/B heaters to the 5A/B heaters respectively.

5A/B also receive east side cross-under drains.

Question 5

How is level controlled in E-5A/B?

Answer 5

Controlled by the valve “disc operating position”, which is influenced by the sum of the torques around the disc hinge pin (i.e., flow momentum, disc weight, bushing friction forces, etc.

Essentially weighted check valves in the drain lines to T-5, MSR Drain Tank.

High level in E-5A/B causes, E-6A/B Level control valve to close (on drain line)

High level in E-6A/B, High Level Dump opens to main condenser.

Question 6

What is the high pressure portion of the extraction and heater drain system?

Answer 6

High pressure components.

• High Pressure Turbine
• Feedwater Heaters, 6A/B and 5A/B.
• Moisture Separator Drain Tank, T-5
• Heater Drain Pumps, P-10A/B

Question 7

What are the low pressure components of the extraction steam and heater drain system?

Answer 7

Low pressure components.

• Low Pressure Turbine
• Feedwater heaters 4A/B, 3A/B, 2A/B, 1A/B.
• Drain Coolers 7A/B

Question 8

What happens if feedwater heater level is maintained too high?

Answer 8

Result in tubes covered with liquid phase and not receiving heat transfer though latent heat of vaporization as steam condenses.

• Heater drain temperatures rise
• Feedwater out temperature lowers

Question 9

What happens if a feewater heater level is maintained too low?

Answer 9

Results in steam blowing through heater. Reduction in heat transfer as steam is not kept in heater to condense (latent heat of vaporization).

• Heater drain temperatures rise.
• Feedwater out temperature lowers.

Question 10

How does the MSR control system ramp function work?

Answer 10

Ramp

Normally used at 30% load after the shutoff valves are opened. This button energizes the circuit that regulates the opening of the 6” Reheater steam control valves CV-0594, 0595, 0597 and 0598 to MSRs E-9A, B, C and D respectively over a period of two hours.

The ramp feature assures an acceptable rate of differential expansion between the LP turbine casing and rotor.

Question 11

Why do have the MSR control system?

Answer 11

Used to insure proper heating of the LP turbine during cold startups,

Minimum differential steam - Protects against thermal stress and possible distortions of the L.P. turbine stationary parts.

Question 12

What steam load does the MSR represent when placed in service?

Answer 12

3 to 5%

Question 13

What does the reset push button do on the MSR control panel?

Answer 13

resets the controller and shuts the reheat control valves.

Question 14

How does MSR manual control function?

Answer 14

Manual Set Point Knob

Positioned at the procedurally prescribed rate/position. Opens Reheater steam control valves to some position immediately.

SOP-8 table must be adhered to for the same reasoning as the RAMP feature or possible LP Turbine damage could occur do to differential expansion of the turbine casing and rotor.

Question 15

What are the MSR control interlocks?

Answer 15

Turbine trip

Control valves are automatically closed

Prevents flooding the reheater drain tanks and feedwater heaters E‑6A/B. This reduces the possibility of a water hammer.

The trip relay (386/AST) must be reset to enable control of the reheat control valve.

Question 16

What supplies control power to the MSR panel and what happens on loss of power?

Answer 16

MCC-1 via L-25A, Breaker #5

Upon loss of power to the control panel, all CVs close. They do not auto re-open when power is restored

Question 17

Tank 4A/B receives what and drains to where?

Answer 17

T-4A Reheater Drain Tank

• MSRs E-9B&D coils

T-4B Reheater Drain Tank

• MSRs E-9A&C coils

T-4A/B normally drains to heaters E-6A/B respectively via air operated level control valves CV-0538/CV-0554. Level controller LC-0538/LC-0554 is the normal level controller for T-4A

Question 18

What is the function of DPIC-0609?

Answer 18

Monitors the differential pressure between T-5 and the E-5s.

With a drop in E-5s pressure DPIC-0609 closes down on CV-0610 to maintain pressure in T-5

Avoics flashing in the P-10 pumps,

• At 75% closed on CV-0610
  
  • DPIC-0609 opens CV-0716 and CV‑0717
  • Provides subcooling condensate to the suction of the P-10 pumps.

Question 19

How does the controller for CV-0610 function?

Answer 19

CASCADE (C) - This is the normal mode of operation.

• Blue indicates T-5 pressure.
• Red pen indicates E-5 Feedwater Heaters pressure.
• Output signal to CV-0610 is indicated on the horizontal meter.

AUTO (A) -

• Red pen indicates E-5 Feedwater Heaters pressure.
• Blue pen is controller setting indicator.
  
  • Adjusted using the ‘SET’ arrow pushbuttons
  • Adjust the Blue pen to T-5 pressure. The controller program will adjust CV-0610 opening to maintain E‑5 pressure (Red pen) greater than the Blue pen setting.
• Output signal to CV-0610 is indicated on the horizontal meter.

MANUAL (M) -

• Red pen indicates E-5 Feedwater Heaters pressure.
• Blue pen indicates T-5 pressure.
• Using the lever at the bottom of the controller controls CV‑0610.
  
  • Maintain CV-0610 open as long as E-5 heater pressure is greater than T-5 pressure.
• Signal to CV-0610 is indicated on the horizontal meter.

Question 20

How are mode changes handles for CV-0610’s controller?

Answer 20

Mode shifts between “C”, “A”, and “M”, are allowed in all but one direction. The one exception is Manual to Cascade. To go to Cascade (C) from Manual (M), the “A” button must first be pushed.

Question 21

How is level in T-5, MSR Drain Tank handled?

Answer 21

CV-0608 P-10A/B Discharge modulates

T-5 level based on input from normal level controller LC- 0608

Normal level: 60% to 65 %. 66% should be full open

Question 22

How does main feed pump suction pressure interact to T-5 level control?

Answer 22

Low suction pressure of 270 psig sensed by PS‑0786

• Overrides the normal level control signal by deenergizing SV‑0786 bleeding air off of CV-0608
• Causes CV‑0608 to fail open.
• Increases Main Feedwater pump suction pressure to help prevent a low suction pressure trip at 250 psig

Question 23

How is high level in T-5 sensed and controlled?

Answer 23

80% sensed by level controller LC-0609

Opens control valve CV-0609 directing water to the condenser directly from T-5.

Question 24

Discuss P-10A/B function, design and power supplies.

Answer 24

• Power Supplies: Both pumps - Bus 1E
• Provide roughly 6100 gpm flow to Main Feed Pumps at 350 psig.
• Mini-flow lines are provided for each pump around the CV-0608. Normal flow is approximately 250 gpm per pump.

Question 25

What trips P-10A/B Heater Drain Pumps?

Answer 25

T‑5 low level 2/2 on LS-0608 and LS-0629

• P-10B at 22.5%
• P-10A at 12.5%

Overcurrent

Indirectly from SIAS since Bus 1E is Loadshed

Question 26

What controls are in the control room for feedwater heater level control?

Answer 26

Handswitches for High Level Dump valves only.

Note E-5s are controlled via E-6s normal level control valve and/or T-5 Check valve/pressure difference.

Question 27

How is high level in E-5A/B Feedwater Heaters Controlled?

Answer 27

High level sensed level switches 0603/0604

E-6A/B level control valves close( SV deenergize)

Loss of DC defeats this feature.

Question 28

How does a loss of instrument air impact feedwater level control?

Answer 28

All NORMAL level control valves fail CLOSED

All high level DUMP valves fail OPEN.

Question 29

How does the Extraction Steam and Heater Drain System interface with the feedwater system?

Answer 29

The Heater Drain pumps discharge into the suction of the MFW pumps.

Feedwater flows through the tubes of the E-6 heaters.

Question 30

How does the Extraction Steam and Heater Drain System interface with the condensate system?

Answer 30

• Condensate pumps supply seal cooling to the heater drain pumps as well as supplying subcooled water to the suction of the heater drain pumps (CV-0716, CV‑0717) as called for by the T-5 pressure controller.
• Hotwell is a collection reservoir for the drains leaving the E-7A/B drain coolers, to be pumped back into the condensate system.
• Heater shell vents and MSR vents are directed back to the condensers.
• Condensate flows through the tubes of the E-5 , 4, 3, 2, 1 heaters and the E-7 drain coolers..
• Seal Water supply to the Heater Drain pumps.

Question 31

How does the Extraction Steam and Heater Drain System interface with the main turbine system?

Answer 31

• Extraction steam is taken from the HP and LP Turbines as well as the HP Turbine exhaust.
• Turbine trip circuit trips closed the MSR steam supply valves and isolates air to the BTVs allowing them to close

Question 32

How does the Extraction Steam and Heater Drain System interface with the main steam system?

Answer 32

Provides heating steam to the MSR heating coils to heat the HP Turbine exhaust prior to entering the LP Turbine.

Question 33

How does the Extraction Steam and Heater Drain System interface with the instrument air system?

Answer 33

Provides motive force for operation of BTVs, heater level control valves T-5 and T-4 level control valves and MSR steam control valves.

Question 34

How does the Extraction Steam and Heater Drain System interface with the plant heating system?

Answer 34

Extraction steam supplies heating steam when >35% power.

Plant heating supplies vent path for Flash Tank

Question 35

What are the effects on the HED system of bypassing heaters?

Answer 35

Colder feedwater from bypass of lower pressure heaters can result in lower shell pressures in up-stream feedwater heaters, causing excess extraction flow into those heaters. This can result in a high level condition, as normal drain cannot handle volume.

Reduction in shell pressure can result in flashing in shell which can cause false level in hot sensing lines, leading to further transients and system upsets.

Reduction in shell pressure can also lead to condensate induced water hammer from up stream drains.

Excessive extraction flow can worsen Flow Accelerated Corrosion (FAC) in extraction lines and Heater shells.

Question 36

What is a heater stage?

Answer 36

A Heater Stage may be an individual Feedwater Heater or, when considering
both Feedwater Trains, a stage may consist of two heaters.

Example: E-3A is one heater stage (a third stage) while E-3A and E-3B are considered one stage of Feedwater Heating (also, a third stage).

Feedwater Heaters E-3A and E-4A are considered two stages of Feedwater Heating (a third and fourth stage).

E-7A and E-7B, Drain Coolers, are NOT considered to be a heater stage.

Question 37

What heaters can be completly isolated during plant operations?

Answer 37

The only Feedwater Heaters that can be completely isolated during Plant
operation are E-3A, E-3B, E-4A, E-4B, E-6A, and E-6B.

Question 38

What must be done if two stages of feedwater heating are bypassed?

Answer 38

Turbine load is restricted to less than 600 MWe to prevent excessive extraction steam velocity in the next higher pressure heater.

Heaters are to be bypassed before the load is lowered unless E-5A/B, which requires E-6A/B bypassed, which requires load reduction to 97% prior to isolating an E-6.