LOCA

Question 1

State the 7 major mitigating strategies for the LOCA ORP

Answer 1

1. Maximize SI flow into the RCS and attempt to isolate the leak. Reduces core uncovery risk.
2. If isolated, regain RCS press. and inventory control while maintaining RCS heat removal
3. If isolatged, perform a controlled CD to SDC entry conditions: 300F, 385psi.
4. If unisolable, rapid cooldown using SGs. particularly important for SBLOCAs
5. If unisolable, commence post LOCA long term cooling. in 2-3 hrs line up simultaneous hot and cold leg inj.
6. If unisolable, make determination on SDC for small breaks or simult. hot and cold leg inj. large breaks.
7. For ISLOCAs, RCPs must be stopped and affected HP seal cooler isolated after the NC cont isolation valves are closed.

Question 2

How does the plant respond to the following:

SBLOCA

LBLOCA

LD line break

ISLOCA
PZR steam space

Answer 2

• SBLOCA: loss of inventory with a gradual pressure drop. mitigation is to depressurize the plant rapidly so that SI can keep core covered. Heat removal is SGs.
• LBLOCA: rapid plant depressurization < 200 psia. Core cooled by SI flow and break flow. No SGs, they are heat source. RAS at 9.4%
• LD line break: gradual depressurization of RCS and incr. Aux Bldg radiation.
• ISLOCA: RU-2, 3 or 6 rising rad levels, exp tank levels rising, only gradual RCS press decrease. Concern is release of radiation to environment.
• PZR steam space: initial drop in Lpzr and Prcs. As bubble forms in RCS, Lpzr rises and Pzr goes solid.

Question 3

Use mollier to determine status of safety valves on the pressurizer.

Answer 3

Find enthalpy of saturated vapor(Ppzr) on mollier.

Plot point on saturation line.

Draw horizontal(constant enthalpy process) to the pressure that corresponds to where the device is relieving to. Normally to the RDT but may be to Pcont.

If below the saturation line, follow pressure line(curving line) up to sat line to determine correct temperature. If above, compare point to constant temperature line( should be superheated).

Question 4

State SFSCs for Rx control as they pertain to LOCA

Answer 4

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

Question 5

State the SFSCs for MVA as they pertain to LOCA

Answer 5

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 PNB-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.

Question 6

What is meant by bus plus and how is it met?

Answer 6

Intent is to ensure power is available to support and maintain control of safety functions. Minimum electrical power is: at least one vital 4.16kv bus, one each of vital AC and DC 120(5) buses.

PK and PN are required to be on the same train as the 4.16kv bus.

Must also have power to equipment needed to maintain other safety functions.

Question 7

State the RCS inventory control SFSCs as they pertain to LOCA

Answer 7

May be met by either:

1. Condition 1
   
   1. Lpzr > 10%[15%]
   2. RCS 24F[44F] or more subcooled
   3. RVLMS > 16% in RVUH or more.
2. Condition 2
   
   1. SI flow adequate per App2
   2. CET and RCS subcooling < 44F[60F] superheat and not rising.

Question 8

State the RCS pressure control SFSCs as they pertain to LOCA

Answer 8

1. Condition 1
   
   1. Ppzr within P/T limits
2. Condition 2
   
   1. SI flow is adequate per App 2

Question 9

State Core heat removal SFSCs as they pertain to LOCA

Answer 9

CET and RCS subcooling < 44F[60F] superhead and not rising.

Question 10

State the basis for superheat value given in Core heat removal SFSC

Answer 10

Core uncovery and superheat are indications that approach to ICC conditions is occuring. Since 62F of instr inaccuracy could be experienced, that is the allowed superheat value. should review earlier efforts for effectiveness.

Question 11

State the RCS heat removal SFSCs as they pertain to LOCA

Answer 11

At least one SG has 45-60%NR[45-60%NR] or FW is restoring at least one sg to the above.

AND
Tc is stable or lowering.

Question 12

State the Cont Isolation SFSCs as they pertain to LOCA

Answer 12

1. Condition 1
   
   • NO valid steam plant activity or rise.
   • Pcont < 3psig
   • No valid containment area or radiation alarms or rise in activity
2. Condition 2
   
   • NO valid steam plant activity radiation alarms or unexplained rise in activity
   • CIAS actuated.

Question 13

State the Cont Temperature and Press SFSCs as they pertain to LOCA

Answer 13

1. Condition 1
   
   • Tcont < 235F
   • Pcont < 8.5psig
   • Hconc < 1.1%
2. Condition 2

• Cont spray header > 4350 gpm
• Pcont < 55 psig
• Hconc < 4.9%

Question 14

State the basis for Tcont of < 235F in SFSCs for LOCA

Answer 14

T cont of 235F is the saturated vapor temperature corresponding to CSAS setpoint.

Question 15

How is restoration of NC different in teh EOPs and why?

Answer 15

To restore NC to containment in the EOP, first open the Supply valve. This allows the inside containment reliefs to lift, expelling any steam or vapor in the piping and preventing water hammer in other parts of the system.

Question 16

Given an ISLOCA, state the indications of an RCS to NC(or EW), LD line, or HPSC leak.

Answer 16

Surge tank level and or pressure rising. RU-2, 3, 6 alarms.

For a LD line leak, BPCVs would be closing as RCS pressure at the NC hx goes down due to the leak.

For a HPSC leak, inlet temperature goes high, NC flow and temperature from associated RCP would go high.

Question 17

When should RCPs be secured during a LOCA?

Answer 17

If Ppzr < SIAS setpoint and remains, secure 1 RCP in each loop

If RCS subcooling < 24F, then stop all RCPs

Also check App 16 RCP parameters.

Question 18

Why is normal containment cooling not established if a RAS has actuated?

Answer 18

If ras actuated, normal containment cooling is not restored due to potential for submergence and eventual failure of inside containment isolation valves associated with NC and WC systems.

Question 19

Why is it benefical to restore normal containment cooling if a RAS has not occurred?

Answer 19

Allows normal containment cooling to maximize recirulation of containment atmosphere. minimizes the potential for H2 pockets and removes heat from containment to facilitate stopping CS sooner.

Question 20

How is containment cooled during a LOCA ORP?

Answer 20

If Pcont > 8.5 psig, then it is by CS spray and shoudl be > 4350 gpm.

If SIAS actuated and containment level not indicated, then restore normal containment cooling.

If < 5psig and cooling restored, then stop CS one train at a time, assessing in between

Question 21

State TCA for H2 analyzers in service

Answer 21

within 30 minutes of LOCA event.

Question 22

During a LOCA what are the reactivity effects of a controlled cooldown?

Answer 22

As the cooldown is preformed, SDM requirements will change. Boration during the cooldown is required as well as RCS sampling. STA is directed to determine RCS boron needed to ensure > 1% SDM during entire cooldown.

Question 23

State TCA for cooldown to SDC entry, and how it is met.

Answer 23

From start of the SBLOCA, SDC entry conditions must be met within 5.8 hrs. This is accomplished by a controlled cooldown of < 100F/hr.

Must reach SDC entry before containment buiding failure occurs.

Question 24

What actions are necessary if the RCS becomes over subcooled?

Answer 24

PTS concern:

stop the cooldown

Depressurize the RCS

If HPSI throttle criteria met, contrl charging, LD and HPSI

If RCS CD rate is exceeded, stop the cooldown and soak until the rate is within limits. then resume.

Question 25

WHen is it permissible to exceed 65%[64%] Lpzr upper limit?

Answer 25

If HPSI throttle criteria not met and Lpzr is too high, or water solid ops is required to maintain Subcooling margin, Lpzr will be maintained higher.

Question 26

Why is it necessary to isolate aux bldg sumps from the LRS system?

Answer 26

two reasons:

isolates the aux bldg when a loca outside containment occurs. minimizes radioactive release

After a RAS, RCS water circulates thru the aux bldg. any leakage will collect in the sumps. they are isolted prior to a RAS to ensure that no radioactive release to environment occurs via the LRS.

Question 27

With RCPs secured and a LOCA, what will happen to Lpzr during RCP restart?

Answer 27

When RCP started, Lpzr will drop due to void collapse, and contraction may occur, dropping Prcs.

If SG is hotter than RCS, a Lpzr and Ppzr rise may occur as heat is input into RCS.

Question 28

Describe the process of reflux, or two phase natural circulation.

Answer 28

Steam leaves the core, reaches top of u tubes and condenses, falling back down as condensate and flowing back into core via hot leg. Some of the steam, as it condenses in the top of the u tubes falls into the cold leg and returns to the core to be boiled off and restart the process.

Question 29

How is two phase natural circulation monitored for effectiveness.

Answer 29

Must establish aux feed to SG and steam it via ADV. Monitor REP CET to confirm the adequacy of heat removal process.

Operators must:

Ensure all available CHPs are operating

SI flow is adequate

SG is at 45-60%NR or being fed to that level

CET subcooling < 44F[60F] superheat and not rising.

Question 30

If RWT level lowering and it does not have a corresponding rise in containment level, what are the actions?

Answer 30

Loca is outside containment.

RWT level must be maintained above the RAS setpoint by makeup.

Question 31

Why is a RAS not initiated early?

Answer 31

May cause insufficent water volume in containment.

loss of suction to SI pumps.

SI pumps have adequate NPSH when the full volume of the RWT above 9.4% has been transferred to containment.

Question 32

What parameters will change and how will they do so following a RAS?

Answer 32

Lpzr or Rx vessel level may lower as LPSI pumps are stopped. Trcs and Tcont, Pcont may rise as the RWT water is no longer removing heat. These are expected trends

Question 33

What is the minimum HPSI flow follwoing a RAS and why?

Answer 33

> 250gpm.

There is no miniflow following a RAS. If not met, the lower flow hpsi pump is stopped.

Question 34

Why must SITs be isolated on a forced cooldown?

Answer 34

Prevent N2 gas from being injected into the RCS, which could blanket and block 2 phase flow in the SGs. Could also lead to air binding SI pumps.

Question 35

What is simultaneous hot and cold leg injection and when is it required?

Answer 35

ensures continued heat removal from core following LOCA when:

RCS subcooling < 24F[44F], based on REP CET.

Lpzr < 10%[15%]

RVUH is < 16% level.

aligned between 2 and 3 hrs following a LOCA.

Question 36

Describe the bases for the times associated with simultaneous Hot and Cold Leg inj.

Answer 36

2 hrs:

steam from break may prevent water from reaching the vessel.

3 hrs:

ensures that buildup of boric acid is terminated well before the potential for boric acid precip occurs.

Question 37

If during a LOCA and the leak has been isolated, how is the plant controlled from a water solid condition?

Answer 37

if water solid, maintain Ppzr with in P/T limits by:

controlling RCS temperature.

Throttle SI flow if criteria are met.

Question 38

How does App 15 help control voids in the RCS?

Answer 38

stop using Aux spray, energize avail Pzr htrs, and vent the RCS head if necessary.