Main Steam(SM)

Question 1

What is the purpose of the Main Steam System?

Answer 1

1. Transport steam from the Steam Generators to the High Pressure Turbine and auxiliary equipment.
2. Steam Generator PORVs and Safety Valves provide over pressure protection for the Main Steam System.

Question 2

What is the system designator for the Main Steam System?

Answer 2

SM

Question 3

What is the purpose of the Steam Generator Flow Restrictor?

Answer 3

1. Limits the amount of thrust loading during a steam line break
2. Limits the amount of positive reactivity added during a steam line break
3. The differential pressure drop across the flow restrictor is used to measuring steam flow

Question 4

What are the major loads supplied by the Main Steam System?

Answer 4

1. The load upstream of the Main Steam Isolation Valves is the Auxiliary Feedwater Turbine Driven Pump.
2. The loads off of the Main Steam Equalization Header:
   A. High Pressure Turbine
   B. Second Stage heating in the Moisture Separator Reheaters
   C. Main Feedwater Pump Turbines
   D. Main Turbine and Feedwater Pump Turbine Turbine Sealing Steam
   E. Condenser Air Ejectors
   F. Auxiliary Steam System
   G. Steam Dumps

Question 5

What is the purpose of the Steam Generator Power Operated Relief Valves?

Answer 5

1. Prevent lifting of the safety valves during mild pressure transients.
2. Provide a flow path for reactor coolant heat removal when the MSIVs are closed.

Question 6

What is the capacity of each Steam Generator PORV, and what are the relief and reset setpoints?

Answer 6

1. There are four PORVs, one on each main steam line, each with a capacity of 2.5% steam flow.
2. The relief setpoint is 1125psig
3. The reset setpoint is 1092psig

Question 7

Where are the Steam Generator PORVs located?

Answer 7

1. A and D are located in the outer doghouse

2. B and C are located in the inner doghouse

Question 8

Where can the Steam Generator PORVs be operated from?

Answer 8

1. Control Room
2. CAPT Panel
3. Local Handwheel

Question 9

What will cause an automatic closure of the Steam Generator PORVs?

Answer 9

A Main Steam isolation signal

Question 10

What provides the motive force for opening the Steam Generator PORVs in AUTO?

Answer 10

The Instrument Air System(VI) provides air for opening the S/G PORVs with control in AUTO in the Control Room.

Question 11

What provides the motive force for opening the Steam Generator PORVs in MAN?

Answer 11

In MANUAL control from the Control Room the S/G PORVs are opened from Instrument Air or Nitrogen, whichever is at the higher pressure.

Question 12

How many Nitrogen Tanks are provided for each Steam Generator PORV?

Answer 12

There are two nitrogen tanks that provide a backup source to operate the S/G PORVs.

Question 13

What is the basic procedure for operating the Steam Generator PORVs locally in the field?

Answer 13

1. Unscrew the clevis from manual shaft override.
2. Rotate the hand wheel in the closed direction to expose the actuator shaft.
3. Open the equalizing valve on the side of the PORV.
4. Slide clevis onto the actuator shaft and tighten the set screw.
5. Turn hand wheel to position the valve as observed on the local position indicator scale.

Question 14

What are the time critical aspects of the local manual operation of the Steam Generator PORVs?

Answer 14

1. 10 minutes to reach the PORV
2. 2 minutes to crack the PORV off of its seat
3. 6 minutes to position the PORV to full open

Question 15

What is the purpose of the Steam Generator Safety Relief Valves?

Answer 15

The Steam Generator Safety Relief Valves provide overpressure protection for the Steam Generators and the Main Steam System.

Question 16

How many Steam Generator Safety Relief Valves are there, what is their capacity?

Answer 16

1. There are a total of 20 S/G Safety Relief Valves, 5 on each Main Steam line.
2. The capacity of each Safety Relief Valve is 5%, for a total of 100% combined capacity.

Question 17

What are the relief setpoints of the Steam Generator Safety Relief Valves?

Answer 17

Relief Sepoints:

(4) 1175psig
(4) 1190psig
(4) 1205psig
(4) 1220psig
(4) 1230psig

Question 18

Where do the Steam Generator Safety Relief Valves vent to?

Answer 18

The exhaust is vented above the doghouse roof.

Question 19

What is the purpose of the Steam Generator PORV Block Valve?

Answer 19

The S/G PORV Block Valves are motor operated block valves capable of isolating the PORVs against full open S/G PORV flow, and could be used to limit blowdown should a S/G PORV stick open.

Question 20

What is the purpose of the Main Steam Isolation Valves?

Answer 20

The Main Steam Isolation Valves stop the uncontrolled steam flow from the Steam Generators in the event of a break in the main steam piping.

Question 21

How are the Main Steam Isolation Valves positioned, and how do they fail?

Answer 21

1. The MSIVs are air operated

2. The MSIVs fail closed on a loss of air or power due to spring pressure.

Question 22

What is the design closure time of the Main Steam Isolation Valves?

Answer 22

8 seconds

Question 23

What will cause an automatic closure of the Main Steam Isolation Valves?

Answer 23

A Main Steam Isolation Signal

Question 24

What is the purpose of the Main Steam Isolation Bypass Valves?

Answer 24

1. Slowly warm down stream piping
2. Equalize pressure across the MSIVs
3. Supply Main Steam to miscellaneous auxiliary equipment

Question 25

What will cause an automatic closure of the Main Steam Isolation Bypass Valves?

Answer 25

A Main Steam Isolation Signal

Question 26

What additional use do the Main Steam Isolation Bypass Valves have while operating in the EPS?

Answer 26

They can be utilized for cooldown following a DBE

Question 27

What is the purpose of the Main Steam Line Condensate Drains?

Answer 27

Drain condensed steam out of the steam lines to prevent water hammer and damage to the Steam Generator Safety Relief and PORVs.

Question 28

What happens when the Main Steam Line Condensate Drain loading is high enough to exceed the capacity of the normally aligned drain orifice?

Answer 28

The orifice drain valve will automatically open to assist in draining condensate from the steam lines.

Question 29

What Main Steam components will close on a Main Steam Isolation Signal?

Answer 29

1. Steam Generator PORVs
2. Main Steam Isolation Valves
3. Main Steam Isolation Valve Bypass Valves
   * Either train will close all valves*

Question 30

What are the Main Steam Isolation Signals?

Answer 30

1. Manual
2. Hi-Hi Containment Pressure - 2/4 channels greater than or equal to 3.0psig
3. Low Steam Line Pressure - 775psig, active greater than P-11
4. High Steam Pressure Rate of Decrease - 2/3 channels on ONE main steam line greater than or equal to 100psig/second up to 2psig/second for 250 seconds.

Question 31

What is the affect of a Main Steam Isolation signal on a S/G PORV in AUTO?

Answer 31

The PORV will close and remain closed until the Main Steam Isolation and the PORV are reset.

Question 32

What is the affect of an automatic Main Steam Isolation signal on a S/G PORV in MANUAL?

Answer 32

The PORV will shift to AUTO and close, but MANUAL can later be selected and the PORV can be opened.

Question 33

What is the affect of a MANUAL Main Steam Isolation signal on a Steam Generator PORV in MANUAL?

Answer 33

The S/G PORV will stay in the MANUAL mode and stay open.

Question 34

What are the requirements for entry into a space that has a high pressure steam relief device in accordance with plant procedures?

Answer 34

Personnel whose work requires entry into the Main Steam Doghouses should be aware of the potential for the automatic release of steam from relief devices during abnormal conditions with the unit Modes 1-4.