Steam Generators(SG)

Question 1

What is the purpose of the Steam Generators?

Answer 1

1. The Steam Generators transfer heat from the primary to the secondary feedwater to produce steam during normal operation.
2. While shutdown in Mode 3 and in Mode 4 when temperature and pressure are above the ND system operating conditions they remove core decay heat and reactor coolant pump heat.
3. During emergencies the S/Gs are a vital part of accident mitigation for removing decay heat from the core.

Question 2

What is the purpose of the Steam Generator Blowdown and Blowoff System?

Answer 2

The Steam Generator Blowdown and Blowoff System removes non-volatile chemical buildup from the S/G tube sheet area to maintain proper steam generator chemistry.

Question 3

What is the system designator for the Steam Generator Blowdown and Blowoff System?

Answer 3

BB

Question 4

What is the purpose of the Steam Generator Wet Lay-Up Recirculation System?

Answer 4

The Steam Generator Wet Lay-Up Recirculation System protects the steam generators from corrosive attack during periods of inactivity. This is accomplished by ensuring the exclusion of oxygen from the steam generators and by maintaining the water mass of the steam generators at the proper pH while under wet lay-up conditions.

Question 5

What is the system designator for the Steam Generator Wet Lay-Up Recirculation System?

Answer 5

BW

Question 6

How many Blowdown Taps do the Unit 1 Steam Generators have, and where are they located?

Answer 6

1. The Unit 1 Steam Generators have two blowdown taps.

2. The blowdown taps penetrate the S/G tube sheet, with one on the Hot Leg side and one on the Cold Leg side.

Question 7

How many Blowdown Taps do the Unit 2 Steam Generators have?

Answer 7

1. The Unit 2 Steam Generators have only one blowdown tap.

2. Blowdown is removed via a header running horizontally near the surface of the tube sheet.

Question 8

Why is the Unit 2 Steam Generator Blowdown and Blowoff System flow rate restricted?

Answer 8

The Unit 2 BB system flow is restricted to prevent vibration and erosion of the blowdown pipe.

Question 9

What is the purpose of the Tube Bundle?

Answer 9

The Tube Bundle is the collection of tubes which make up the heat transfer surface.

Question 10

What are the major differences in the Tube Bundles between the Unit 1 and Unit 2 Steam Generators?

Answer 10

1. Unit 1 S/Gs have more tubes
2. The outside tube diameter is larger on the Unit 2 S/Gs
3. The total heat transfer area of the Unit 1 S/Gs is considerably larger

Question 11

What is the purpose and description of the Bundle Shroud?

Answer 11

1. The Bundle Shroud encloses the tube bundle.
2. The Bundle Shroud:
   A. Creates a boundary between the region where the boiling occurs and the area where level is measured.
   B. Creates a path for steam flow from the tube bundle area to the water separators.
3. The bottom of the Bundle Shroud is a few inches off of the tube sheet.

Question 12

What is the purpose of the Primary Deck?

Answer 12

The top of the Bundle Shroud is the Primary Deck. Riser pipes of the primary steam water separators penetrate the primary deck creating the flow path for steam to exit the tube bundle.

Question 13

What is the purpose of the Downcomer Region?

Answer 13

The Downcomer Region is the space between the Bundle Shroud and the Steam Generator Shell. The Downcomer collects the feedwater , and the recirculation flow, then routes it to the Tube Bundle region.

Question 14

What is the difference between the Unit 1 and Unit 2 feedwater flow after it has entered the Steam Generator Shell.

Answer 14

1. In the Unit 1 S/Gs all of the feedwater flow is through the downcomer.
2. In the Unit 2 S/Gs only feedwater admitted through the auxiliary feedwater nozzles enters the downcomer.

Question 15

What type of Primary Separators do the Unit 1 Steam Generators use?

Answer 15

The Unit 1 S/G Primary Separators have nozzles that cause the steam to leave in a swirling motion using centrifugal force to remove moisture from the steam.

Question 16

What type of Primary Separators do the Unit 2 Steam Generators use?

Answer 16

The Unit 2 S/G Primary Separators have stationary blades, much like propeller blades, to force the steam to swirl removing moisture.

Question 17

What type of Secondary Separators do the Unit 1 Steam Generators use?

Answer 17

The Unit 1 S/G Secondary Separators have vanes that continue to cause the steam to leave in a swirling motion using centrifugal force to remove moisture from the steam.

Question 18

What type of Secondary Separators do the Unit 2 Steam Generators use?

Answer 18

The Unit 2 S/G Secondary Separators are chevron type moisture separators. The arduous path removes moisture from the steam as its forced to change direction.

Question 19

What is the quality of the steam leaving the Secondary Separators for the Steam Generators of both units.

Answer 19

99.75%

Question 20

What is the purpose of the Secondary Deck?

Answer 20

The Secondary Deck is the outlet of the Secondary Separators. This boundary forces steam through the secondary separators before it exits the Steam Generators.

Question 21

What is the purpose of the Steam Outlet Nozzle?

Answer 21

The Steam Outlet Nozzle restricts steam flow out of the Steam Generator for two reasons:

1. Reduce the thrust load on the Steam Generators during a steam line break so they don’t twist in their mounts.
2. Reduce the amount of flow to limit the primary cooldown rate.

Question 22

What is another purpose of the Steam Outlet Nozzle related to normal operation?

Answer 22

The Steam Outlet Nozzle serves as a steam flow orifice for steam flow measurement.

Question 23

What is the design of the Main Feedwater Nozzle for the Unit 1 Steam Generators?

Answer 23

1. Feedwater enters the S/G through a thermal sleeve above the transition cone.
2. Immediately after entering the S/G the line forms a “goose neck” which helps to protect the penetration from thermal stress.
3. After the “goose neck” the feed is directed down to the feed ring. The feed actually leaves from the top of the feed ring to ensure it remains full during level transients.

Question 24

What is the design of the Main Feedwater Nozzle for the Unit 2 Steam Generators?

Answer 24

1. Feedwater enters the S/G near the bottom on the Cold Leg side.
2. The CF line penetrates the Bundle Shroud and enters the Preheater which is a series of baffles used to split flow.
3. The baffles keep CF in contact with the Cold Leg longer improving thermal efficiency.

Question 25

What two problems were created by the use of the Preheater arrangement in the Unit 2 Steam Generators?

Answer 25

1. Water hammer during low flow conditions

2. Vibration due to high flow

Question 26

What was the fix for the Preheater arrangement used in the Unit 2 Steam Generators?

Answer 26

Splitting flow between the main and auxiliary feed nozzles

Question 27

What is the design of the Auxiliary Feedwater Flow Nozzles?

Answer 27

1. In both units the Auxiliary Feedwater Nozzle enters above the Primary Deck below water level.
2. The upturn in the end of the nozzle ensures the pipe remains filled during transients that cause water level to drop below the level of the nozzle. This would cause steam to enter the nozzle and when auxiliary feed was established there would be a significant thermal stress.

Question 28

What is the purpose of the Primary Head?

Answer 28

1. The Primary Head is located on the bottom of the S/Gs for both units and separates the flow paths going into and leaving the U-tubes.
2. The reactor coolant Hot and Cold Legs attach to the Primary Head, and the top of the Primary Head is the Tube Sheet.

Question 29

When is Tempering Flow aligned to the Auxiliary Feedwater Nozzles on the Unit 1 Steam Generators?

Answer 29

When CF flow rises above 15% flow, flow is shifted from the CA Nozzles to the CF Nozzles, so Tempering Flow is aligned to the CA Nozzles.

Question 30

What maintains the temperature of the CF Nozzles on the Unit 1 Steam Generators when CF is aligned to the CA Nozzles at flows of less than 15%?

Answer 30

Reverse Purge will allow a small amount of water from the Steam Generator to flow through the CF Nozzles and back to the Condenser to maintain CF Nozzle temperature.

Question 31

When is Tempering Flow aligned to the Auxiliary Feedwater Nozzles on the Unit 2 Steam Generators?

Answer 31

When CF flow rises to 15% flow, flow is shifted from the CA Nozzles to the CF Nozzles so Tempering Flow is aligned to the CA Nozzles.

Question 32

What maintains the temperature of the CF Nozzles on the Unit 2 Steam Generators when CF is aligned to the CA Nozzles at flows of less than 15%?

Answer 32

Reverse Purge will allow a small amount of water from the Steam Generator to flow through the CF Nozzles and back to the Condenser to maintain CF Nozzle temperature.

Question 33

When is Tempering Flow no longer required for the Unit 2 Steam Generators?

Answer 33

When flow rises to approximately 40% the orifice creates enough back pressure that there is sufficient flow from Feedwater to force CF water through the Auxiliary Feedwater Nozzles while most of the flow goes through the CF Nozzles.

Question 34

What are the precautions associated with Steam Generator entry?

Answer 34

1. The Steam Generator is considered a Confined Space.
2. Hazards associated with entry into the Steam Generators are:
   A. Insufficent Oxygen
   B. Hydrazine Exposure
   C. Radiation Exposure

Question 35

What will cause the Steam Generator Blowdown and Blowoff System Containment Isolation Valves to automatically isolate?

Answer 35

1. Phase A Isolation Signal
2. CA Auto Start
3. Transfer to the SSF

Question 36

Which Steam Generator Blowdown and Blowoff System Containment Isolation Valves receive power from which train?

Answer 36

Inside Containment Isolation Valves - Train A Power

Outside Containment Isolation Valves - Train B Power

Question 37

How is Steam Generator Blowdown flow controlled?

Answer 37

The BB line from each Steam Generator contains a flow control valve located close to the BB Tank. The flow control valves are controlled from the Control Room.

Question 38

What will cause an automatic closure of the BB Flow Control Valves?

Answer 38

1. CA Auto Start
2. BB Tank High Pressure of 190psig
3. BB Tank Hi-Hi Level
4. EMF-33 Trip 2(High Radiation)

Question 39

What are the safety hazards associated with the BB Tank?

Answer 39

1. The BB Tank is a confined space
2. Hazards associated with entry:
   A. Inadequate Oxygen
   B. High energy water and steam in Modes 1-4
   C. Hydrazine exposure
3. When handling resin PPE requirements are:
   A. Safety goggles
   B. Lab coat
   C. Lab gloves
4. Spilled resin can present a slip hazard
5. S/G tube leak can present a radiation hazard

Question 40

What is the Steam Generator Wet Layup System generic flow path?

Answer 40

1. Spectacle flanges are installed to isolate the low pressure piping of the BW system from the CA and BB piping. These flanges have to be swung to align the flow path.
2. The BW pump takes a suction off of the CA line in between the isolation valve and the Containment Penetration.
3. Water is pumped back to the S/Gs:
   A. The Unit 1 S/G BW flow has a connection that goes directly into the Tube Bundle Shroud.
   B. The Unit 2 S/G BW flow is discharged directly in the S/G through the BB nozzle at the Tube Sheet.

Question 41

What is the capacity of the Steam Generator Wet-Layup Pumps?

Answer 41

1. Each S/G has a 100% capacity pump rated for 100gpm

2. The flow rate recirculates the entire volume of water every 5 hours

Question 42

What is the power supply to the BW Pumps?

Answer 42

600 VAC Unit Power

Question 43

What inlet temperature will isolate Steam Generator Blowdown flow to the BB Demineralizers?

Answer 43

Greater than or equal to 160F

Question 44

What hazards are monitored for when entering the Backwash Tank Pit?

Answer 44

1. Ammonia
2. Hydrazine
3. Oxygen