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Secondary Systems > Main Steam > Flashcards

Main Steam Flashcards

0
Q

Where can the SG system send steam to for condensing?

A

Main condenser or atmosphere

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1
Q

What’s the purpose of the main steam system?

A

Delivers steam from S/G to HP turbine over the entire operating range. Also provides steam to:

1) moisture separator re-heaters
2) feed water pump turbines
3) steam seal system for the main turbine and feed water pump turbines
4) AFP turbine
5) aux steam system

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2
Q

How does the SG system cool down the plant if a condenser is not available?

A

Atmospheric dump valves (ADVs)

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3
Q

Draw main steam.

A

Verify drawing included: down comer isolation valves, economizer isolation valves, S/Gs, SG safety valves, ADVs, MSIVs, MSIVs isolation valves, MSIVs bypass valves, steam traps, steam bypass control valves, all loads

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4
Q

What are the main loads on the SG system?

A

Main turbine, main feed water pump turbine, aux steam system, gland sealing steam, reheat steam to 2nd stage MSR.

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5
Q

What will a loss of feed water cause?

A

Inability to cool the RCS and lead to a plant trip due to low S/G water levels or high pressure

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6
Q

Which valves are impacted by a loss of instrument air?

A

MSIVs and economizer FWIVs use IA to operate the pumps and air for the control system.

Down comer FWIVs, economizer and down comer fw control valves, ADVs, and SBCS valves are all pneumatically operated, use IA for control air, operating air, or both

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7
Q

What is N2 used for in the SG system?

A

To fill accumulators for ADVs, down comer FWIVs and backup for the down comer feed control valve.
Also used for blanketing the s/g during shutdown.

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8
Q

What do the S/G feed water down comer control valves do?

A

Allow precise control of feed to the down comer section of the S/G.
Normally controlled by the digital feed water control system.

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9
Q

What are the down comer block valves used for?

A

Allow remote isolation of the down comer control valves.

Motor operated, gate valves operated from control room

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10
Q

How are the down comer control valves controlled?

A

Pneumatically. Normally from DFWCS, but can be manually controlled from the control room

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11
Q

How does the down comer control valve fail on a loss of power or air pressure?

A

Fails locked (as is)

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12
Q

Describe the operation of the down comer control valve.

A

At low powers, 100% passes through them to ensure sufficient pre-heating for feed water.
Start throttling closed at 15% power and increasing. Economizer opens up (called swap over).
50% power! valve reopens to a set position and supplies about 10% of feed water flow between 50-100% power to provide sub cooling for recirculating water and promote increased recirc ratio in the S/G

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13
Q

When are the down comer bypass control valves used?

A

Mode 3 to control S/G water level using AFP-N

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14
Q

How many trains of down comer isolation valves are there and how are they controlled?

A

Train A and train B (upstream is A). They are normally open, but are pneumatically operated from the control room.

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15
Q

What will cause the down comer isolation valves to not be able to be opened from the control room?

A

If a MSIS is present, the valves won’t open.

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16
Q

How do the down comer isolation valves fail?

A

Loss of DC control power - open

Loss of IA and N2 backup - closed

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17
Q

How can the down comer isolation valves be over ridden with an MSIS present?

A

Place the switch in the close position and observe the white override light is lit. Then take the switch to open

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18
Q

How long will the N2 accumulator last on the feed water down comer isolation valves?

A

Up to 8 hrs.

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19
Q

Why isn’t the economizer feed line not used at low power?

A

Insufficient pre-heating of the feed water

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20
Q

Where are the economizer control valves operated from?

A

Normally controlled by DFWCS but can be operated locally manually or from the control room

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21
Q

How do the economizer feed control valves fail?

A

Loss of air or electrical power- locked (as is)

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22
Q

What happens to the economizer isolation valves on a loss of power? Loss of air?

A

Power- fail closed

Loss of air- no position change to keep them available for fast close

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23
Q

What signal will close the economizer isolation valves?

A

MSIS

24
Q

How/ what methods of operation can the economizer isolation valves be operated in?

A

Slow open/ slow close - solenoid a shift components to block flow to and from accumulators & realign hydraulic pump discharge

Exer/Acc CH TEST - only closes the valve to 90% and reopens it automatically in Exer. Acc CH Test verifies proper N2 pre charge. Also used to bleed off excess pressure from the accumulator.

FAST CLOSE - 5000# accumulators are lined up to the top of the cylinder directly to close the valves (push button)

25
Q

What percentage of the u-tubes can be plugged and still have a fully functioning steam generator?

A

10%

26
Q

What parts make up the secondary side shell?

A

Lower and intermediate shell, transition cone, steam drum, head

27
Q

Describe the flow path from the down comer line inside the steam generator.

A

Feed water enters feed ring; to top of down comer region; combines with moisture separated from the steam water mixture; drains to down comer annulus.

28
Q

What minimizes water hammer in the steam generator?

A

The feed ring distributing feed almost all the way around the down comer region limiting the tube steam space by putting more relatively cold feed water into the Th tube region.

29
Q

Where is the economizer located in the s/g?

A

Just above the tube sheet on the cold leg side.

30
Q

What is the area between the wrapper plate and the shell called?

A

Downcomer

31
Q

What is the water removed by the moisture separators and steam dryers called?

A

Recirculating water

32
Q

Why are the safety valves set to relieve sequentially?

A

To minimize the number of valves required to open during an over pressure condition. This reduces the chance of a safety valve sticking open and over cooling the RCS

33
Q

What holds the relief valve closed?

A

Spring pressure acting on the spindle being transmitted to the disc.

34
Q

What are the S/G relief valve set points?

A

3 lift at 1315psig
1 lifts at 1290psig
1 lifts at 1250psig

35
Q

When are the ADVs used?

A

When it’s necessary to remove heat from the RCS when the main condenser or SBCS is not available (MSIVs are closed)

36
Q

How are the ADVs operated?

A

Air operated with nitrogen backup. Normally from control room but can be operated manually at the valve.

37
Q

When can you use the block valve to isolate the ADVs?

A

Only for maintenance purposes (not to isolate a stuck open ADV)

38
Q

What type of valves are the ADVs?

A

Offset globe valves with internal pilots and self drag velocity control elements.

39
Q

What happens to an ADV on a loss of power or pneumatic pressure?

A

Fail closed on both accounts

40
Q

What does the AO have to do for the ADV accumulator drop test?

A

Take the temperature of the accumulator by connecting to the thermocouple ports at the placards on the accumulators

41
Q

How are the isolation valves and bypass valve for aux feed A feed pump operated?

A

Motor operated or manual at the valve

42
Q

Why does the bypass valve open first when the aux feed A steam supply valves get the signal to open?

A

To provide enough steam to spin the turbine and raise governor oil pressure enough to cause the actuator controlled steam admission valve to start closing before the steam supply valves open.
All this prevents an over speed trip.

43
Q

Which aux feed A starts on an AFAS actuation caused by #2 steam generator low level?

A

Both pumps’ steam supply valves open regardless of which S/G has the low level.

44
Q

Will the aux feed pump A shutdown after the AFAS signal clears?

A

No. It must be manually secured.

45
Q

When is rapid positioning used for the MSIVs?

A

Abnormal conditions and shutdowns

46
Q

What ensures equal wear on the disc of the MSIVs?

A

Revolving disc feature rotates the disc a few degrees during each closing stroke to ensure even wear.

47
Q

What allows us to have 1 MSIV instead of a train A and train B?

A

Each valve has an independent, self contained hydraulic actuator unit and two independent redundant and opposite train powered hydraulic supply systems.
The pump is the only component common to both hydraulic units.

48
Q

What pressure are the accumulators for the MSIVs charged to?

A

5000-5400 psig

49
Q

What ensures the MSIVs can be closed following a loss of offsite power and the IA system?

A

Two air reservoirs.

50
Q

What is the normal power supply for the MSIV?

A

Normally is directly off the battery.

51
Q

What happens to the MSIVs on a loss of air?

A

They do not change position and stay capable of fast closing.

52
Q

How are the MSIV bypass valves operated?

A

Each valve has a train A and B solenoid valve in series with its air supply. If both solenoids energize, air is lined up and the valve overcomes spring pressure to open. You can operate them manually as well.

53
Q

How are the SBCS valves operated at normal power?

A

Remote automatic with SBCVs closed.

54
Q

Where can steam generator blow down flow come from?

A

Down comer, hot leg, or cold leg.

55
Q

Where are the blowdown isolation valves located?

A

In containment

56
Q

What signals isolate S/G blowdown?

A

MSIS, AFAS, or SIAS

There are two valves, an upstream and downstream. One in containment, one outside.

57
Q

When are the wet layup pumps used?

A

During shutdown conditions for re circulation or inventory transfer from the S/Gs.

58
Q

Where can the wet lay up pumps discharge to?

A

Blowdown demins or directly back to the steam generators.

Secondary Systems (36 decks)

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