LOOP/LOFC

Question 1

What are the two safety functions assumed in LOOP/LOFC and how are they maintained?

Answer 1

Reactivity control is maintained in mode 3 hot standby. SDM is assured by CEAs inserted. Tc is held as constant as possible.

Core Heat Removal is maintained by feeding and steaming with ADVs and thru the use of AFA.

Question 2

Identify the concern with RCP coastdown used throughout the safety analysis.

Answer 2

Safety analysis assumes that the RCPs remain energized for at least 3 seconds during a MT trip and LOOP. This additional time along with the coasdown features of the RCPs provides flow for the removal of maximum generated decay heat in the seconds following a trip.

Question 3

Identify the accidents or AOOs that assume a LOOP.

Answer 3

SGTR

ESD

LOCA

LOAF

RCP shaft shear.

Question 4

State the entry criteria that is not obvious for LOOP/LOFC.

Answer 4

A station blackout has occured, at least one 4.16kv bus has been restored from:

EDG, other unit EDG, offsite power.

Subcooled natural circulation is to be used for RCS heat removal although at least one non vital 13.8kv AC bus is energized.

Question 5

What ORP is appropriate when a LOOP/LOFC exists in conjunction with a LOCA, ESD SGTR or LOAF?

Answer 5

LOOP/LOFC is appropriate only when no other major events are in progress.

The specific ORPs covering those events are designed to mitigate them in the face of a loss of nonvital power.

Question 6

Identify the major mitigation strategies for a LOOP/LOFC.

Answer 6

Perform SFSCs to confirm it is the only event occurring.

Place plant in a stable condition.

Either maintain Hotstandby or cooldown to SDC conditions.

Attempt to restore power

IF power restored, restore major plant equipment and restart RCPs.

If power not restored, EOP provides cooldown guidance to place SDC inservice and then transition to GOPs. SDC transition covered by GOP procedures.

Question 7

Why is seal inj. isolated prior to restoring a CHP to operation?

Answer 7

Seal inj. must be isolated to prevent a rapid cooldown of the RCP seals and thus damage. Once a CHP is running, seal inj should be restored.

Question 8

Why is the always running CHP handswitch taken to stop following a LOOP?

Answer 8

With no SIAS or CIAS actuations, the always running CHP will be antipumped. It will subsequently have to be manually started by clearing the antipump. This is done by taking the handswitch to stop.

Question 9

Why is an MSIS initiated on receipt of a LOOP?

Answer 9

Initiating an MSIS prevents overpressurizing the main condenser in the event of a loss of vacuum due to a loss of CW from the loss of offsite power.

SG blowdown is isolated as well by the MSIS to minimize the amount of secondary inventory that is lost.

Question 10

What parameters are checked to ensure natural circulation is occurring and is adequate?

Answer 10

Loop dT is < 65F

Thot and Tcold are constant or lowering

RCS is > 24F subcooled using CET subcooling.

< 30F dT between Thot RTDs and Max quadrant CET temperature.

Question 11

Why is SApp 53 - align deenergized buse performed during a LOOP.

Answer 11

SA 53 opens breakers on the deenergized buses to allow for proper laoding when the buses are reenergized. This sets up the electrical distribution system to be reenergized, it DOES NOT brink power back.

Question 12

Per SA 53 - Aligning deenergized buses, why are the buses checked for tripped relays and when does this have to be performed?

Answer 12

The direction to check deenergized buses for tripped relays and reset if necessary. This SA is at the discretion of the CRS. If the reason is known and there is no possibility of damage to the buses, then there is not need to wait until the inspection is completed before reenergizing buses.

Question 13

State the time limitation associated with energizing NAN-S07 from the SBOG and its basis.

Answer 13

SBOG design assumes that offsite power or the SBOG is available to supply power to the local bus. In the case of a LOOP where DGs start and load, there is no power to the SBOG local bus and therefore no power to the battery chargers. Since those batteries are rated for 1 hour, an SBOG is started within 1 hour so as to maintain the SBOG available to cope with a SBO or interruption of power.

Question 14

WHy is it necessary to energize switchyard loads from the SBOGs?

Answer 14

SWYD loads are supplied from the SBOGs to supplement SWYD batteries and supply power to the arc suppressor air compressors, ensuring SWYD bkr operation.

Question 15

Why would SWYD loads NOT be energized from the SBOGs if they are deenergized?

Answer 15

IF the SWYD is deenergized and BOTH:

• power restoration is not expected in 2 hours.
• thunderstorm activity is not present near PVGS

Then perform SA 54 - Energize SWYD loads from the SBOGs.

If lightning is IN the vicinity of PVGS, SA 54 will NOT BE PERFORMED.

Question 16

State the limitations of the SBOGs to supply more than one unit at a time.

Answer 16

SBOGs can only supply Unit 1 and 2 OR Unit 1 and 3 simultaneously, never 2 and 3.

Question 17

Why is SA 55 and 56 - Restoring a DG to a vital bus performed upon failure of a EDG?

Answer 17

These SAs will provide direction to determine the reason the DG failed to start and load to the bus and attempts to start the EDG. They are performed locally by the ctrl bldg operator. They DO NOT close the DG output bkr but assume it will close automatically or will be done from the CR.

Question 18

Why is it necessary to perform SA 57 and 58, manually tripping the lockout relays associated with the vital bus load breakers when a vital bus is energized by an SBOG or opposite train EDG?

Answer 18

Manually tripping the lockout relays prevents uncontrolled starting of the affected train equipment. A controlled method of energizing loads on the affected train must be performed to prevent overloading the power source.

Question 19

What are the limits on the SBOG for powering one or more unit’s vital buses?

Answer 19

Maximum loading for SBOGs is temperature dependant. Each SBOG is rated at 3.6 MW at an ambient temperature of 116F. At lower temperatures the SBOG can produce more power. Due to cabling limitations the max loading to any one unit from an SBOG is 290 amps(approx 6 MW).

Question 20

How is a vital bus transferred from SGOB power to its associated EDG or Offsite power per SA 60 or 61?

Answer 20

SA 60 is used for paralleling the A EDG with SBOGs. IF 2 SBOGs are running, load is reduced, one SBOG is secured and the EDG is paralleled and load is picked up. Then either the SBOG is shutdown or the incident units supply breaker is opened. This is only possible with PBA-S03(PBB-S04 would be interlocked by the alternate breaker and paralleling would not be possible.)

SA 61 restored offsite power and takes the SBOG off the bus. If 2 SBOGs are running, load is reduced, one SBOG is secured and offsite power is paralleled and load is picked up. Then either the SBOG is shutdown or the incident units supply breaker is opened. When offsite power has been restored up to the normal supply breaker and the SBOG is supplying via PBB-S04, the normal supply breaker is closed, and opening the alternate supply breaker.

Question 21

When is SA 31 Local monitoring of IA pressure and N2 Supply used and what will it accomplish?

Answer 21

A LOOP will result in loss of IA compressors. The lp N2 system automatically backs up the IA system. SA 31 monitors IA pressure and N2 tank lvl and gives direction to manually operate downcomer isolation valves.

Question 22

Why are the major loads on NKN-M46 load shed during a LOOP?

Answer 22

load shedding NKN-M46 supports longer operation of the ESOP(7hrs). The MFW and MT DC lube oil pumps will be stopped. For ONLY Unit 1, if the SBOGs are supplying SWYD loads, NKN-M46 will not be load shed.

Prior to stopping the MT DC Lube oil pumps, the MT must be stopped. Hydrogen should be vented from the MG prior to the ESOP losing power and stopping(7hrs).

Question 23

At what point in the LOOP event is the MG actually purged of H2 with CO2?

Answer 23

The main generator will be vented of H2 but no purge of CO2 is possible until offsite power is restored.

Question 24

Which unit is responsible for energizing SWYD loads?

Answer 24

Unit 1.

Question 25

How is offsite power restored and synchronized with the SBOG?

Answer 25

Only one SBOG is allowed to be paralleled with offsite power. Careful coordination is required between the CR and the SBOG CR.

Question 26

State the SFSCs for RCS inventory control as they pertain to an LOOP/LOFC

Answer 26

• Lpzr > 10%[15%]
• RCS is > 24F[44F] or more subcooled
• RVLMS is > 16% in RVUH

Question 27

State the SFSCs for RCS pressure control as they pertain to an LOOP/LOFC.

Answer 27

Ppzr maintained within P/T limits

Question 28

State the SFSCs for Core Heat Removal as they pertain to an LOOP/LOFC.

Answer 28

Core Heat Removal

• RCS ΔT < 65°F with RCPs off.
• RCS ΔT < 10°F with RCPs running.
• RCS is ≥ 24°F subcooled.

Question 29

State the SFSCs for RCS Heat Removal as they pertain to an LOOP/LOFC

Answer 29

• At least one SG level is 45-60% NR [45-60%NR]

AND

• TC is stable or lowering.

Question 30

State the SFSCs for CMNT isolation as they pertain to an LOOP/LOFC

Answer 30

Pcont < 2.5 psig

No valid containment or steam plant RU alarms or unexplained rise in activity.

Question 31

State the SFSCs for Containment Temperature and Pressure Control as they pertain to an LOOP/LOFC.

Answer 31

Containment temperature:

• < 117°F
• < 125°F during a Loss of Offsite Power
• Containment pressure < 2.5 psig.

Question 32

State SFSCs for Rx control as they pertain to LOOP/LOFC

Answer 32

1. Power lowering or <2x10^-4% and stable or lowering
2. All FSCEAs are inserted OR > 40gpm boration OR SDM verified

Question 33

State the SFSCs for MVA as they pertain to LOOP/LOFC

Answer 33

1. At least 1 vital 4.16kv bus energized
2. At least one of the following(must be on same train as above):
   
   1. PKA-M41, PKC-M43, and PNA-D25
   2. PKB-M42, PKD-M44, and PNA-D26
3. No jeapordized safety functions require restoration of electrical power to avital AC or DC bus. Not met if recovery of equipment is dependant on restoration of power.
4. Diesel Fuel Oil Transfer Pump is maintaining Day Tank level for at least one DG supplying the powered vital AC bus.