EOP-4 LOCA Recovery

Question 1

What’s the difference between a large break and small break LOCA in terms of cooling strategy?

Answer 1

Large Break - only path is through the core and out the break.

Small Break - only path is via steam generators.

Question 2

What are the symptoms of LOCA’s? Small vs Large?

Answer 2

LOCA Symptoms: Initial decrease in PCS pressure and inventory

Large Break: Containment Temperature and Pressure rise

Small Break: Charging/Letdown mismatch, subcooling decrease

Question 3

What are the affects of a LOCA on the Safety Functions?

Answer 3

Primarily Affects

• PCS Pressure, Inventory and PCS/Core Heat Removal

Lsser Degree

• Reactivity control, Containment isolation, and Containment temperature and pressure control are also affected

Question 4

What is the Hierarchy of Safety Functions?

Answer 4

1. Reactivity
2. Maintenance of Vital Auxilliaries - Electric
3. PCS Inventory
4. PCS Pressure
5. Core Heat Removal
6. PCS Heat Removal
7. Containment Isolation
8. Containment Atmosphere
9. Maintenance of Vital Auxilliaries - Water
10. Maintenance of Vital Auxilliaries - Air

Question 5

What is necessary for an unisolable large break LOCA?

Answer 5

Continuous injection is required to make up for the loss out the break and to
prevent boron precipitation

Question 6

How and when is PCS pressure control lost for large and small breaks?

Answer 6

Initially lost as PCS inventory flows out the break.

Large Breaks

• PCS depressurizes in ten seconds to three minutes to pressures typically below 300 psia
• Largest Breaks the PCS equalizes pressure with containment
• Operator never regains PCS pressure control

Small Breaks

• Depressurizes to equilibrium with steam generators in 10 - 30 minutes
• Depressurization follows SG cooldown
• Safety Injection refills PCS and Pressurizer Level/Pressure Control regained

Question 7

What are the operator actions for small break LOCA post level/pressure control being regained?

Answer 7

1. Decreasing PCS pressure by means of auxiliary sprays
2. Controlling HPSI Pumps and Charging
3. Heat removal via the Steam Generators in order to establish shutdown cooling entry conditions
4. Isolating or depressurizing the SITs.

Question 8

What are the criteria for throtteling Safety Injection?

Answer 8

• PCS subcooling meets ONE of the following:
  
  • At least 25°F subcooled for non-degraded Containment conditions
  • Greater than the minimum subcooling curve on EOP Supplement 1 for degraded Containment conditions
• Corrected PZR level is greater than 20% (40% for degraded Containment) and controlled.
• At least one S/G is available for PCS heat removal with corrected level being maintained or being restored to between 60% and 70%.
• Operable RVLMS channels indicate greater than 102 inches above the bottom of fuel alignment plate (621’ 8”).

Question 9

What are the requirements of 10CFR50.46(b) for Emergency Core Cooling Systems?

Answer 9

• The calculated fuel peak centerline temperature does not exceed 2200F.
• The total Zirc water reaction does not exceed 1% of the total Zirc in the core.
• The cladding temperature transient is terminated at a time when the core geometry is amenable to cooling. The fuild cladding oxidation limit of 17% is not exceeded.
• The core temperature is reduced and decay heat is removed for an extended period of time, as required by the long lived radioactivity remaining in the core.
• Core geometry remains intact and coolable.

Question 10

What happens to Power, T_ave, PCS Pressure, PCS Level and Subcooling during a LOCA vs ESDE?

Answer 10

LOCA

• Power unchanged
• T_ave unchanged
• PCS Pressure goes down
• PCS Level goes down
• Subcooling goes down

ESDE

• Power goes up
• T_ave goes down
• PCS Pressure goes down
• PCS Level goes down
• Subcooling goes up

Question 11

What is the basis for the safety function status check of Reactivity in EOP-4, LOCA?

Answer 11

Reactor Wide RangePower less than 10^-6% is the maximum power expected at 15 min post trip.

Wide Range could be fluctuating so Source Range count of 100 cps is given as an alternative.

Question 12

What is the basis for MVAE status check?

Answer 12

In general, the normal electrical power requirements needed to maintain all other safety functions are:

• At least one vital 2400 VAC bus
• At least one of the following groups of vital 125 VDC bus combinations

D11A, D11-1, and D11-2
D21A and D21-1

• 125 VDC Bus D21-2 energized
• At least three of four vital 120 VAC buses

Question 13

What is the basis of the inventory control check in regards to Pressurizer Level,

Answer 13

20% [minimum level for inventory control].

The PZR level limit corresponds to the lowest level which can be accepted before the PZR is considered drained.

Question 14

What is the basis for the PCS subcooling check?

Answer 14

The PCS subcooling limit is based on avoiding saturated conditions (eg, subcooling = 0°F) in the PCS by ensuring some margin to saturation always exists.

The 25°F limit provides some allowance for instrument uncertainties.

Question 15

What is the basis for the reactor vessel level greater than 102 inches above the bottome of the fuel alignment plate?

Answer 15

102 inches above the bottom of fuel alignment plate equates to the top of the hot leg nozzles

The intent of this limit is to ensure the following:

• Adequate PCS inventory control has been established and the core is covered
• Hot legs covered supports natural circulation, prior to stopping or throttling HPSI, or securing from Once-Through-Cooling.

Question 16

What is the basis for checking containment water level less than 595 feet 9 inches? How about 596 feet, 4 inches?

Answer 16

596 feet 4 inches

• HPSI injection valves subject to inoperability due to Containment water level.
• Ensure valves open and breakers open

595 feet 9 inches

• LPSI injection valves subject to inoperability due to Containment water level.
• Ensure valves open and breakers open.

Question 17

Option 2:

Why do we check SI flow within the bounds of EOP Supplement 4 for inventory control?

Operable RVLMS channels indicate greater than 11 inches above the bottom of fuel
alignment plate?

Answer 17

The curves provide implicit assurance that Inventory Control is being
maintained with Reactor Vessel level greater than the top of the fuel

11 inches above fuel plate in conjuction with Supplement 4 curves ensures fuel is covered.

Question 18

How is PCS pressure control satisfied?

Answer 18

Condition 1:

• PCS Pressure Control is satisfactory if the PCS can be maintained within the limits of EOP Supplement 1 [post accident PT curves] utilizing Pressurizer heaters and spray, Charging and SI Pumps. Maintaining the PCS within the limits, maintains the PCS subcooling necessary for single phase natural circulation flow and minimizes the possibility of Pressurized Thermal Shock (PTS).

Condition 2:

• If PCS pressure can not be maintained within the limits of EOP Supplement 1 [post accident PT curves], then PCS Pressure Control is satisfied when SI flow is within requirements of EOP Supplement 4 [minimum required HPSI flowrate] with all available SI Pumps operating and injecting borated water into the PCS. SI flow within the SI delivery curves is based on the minimum design SI flow assumed in the LOCA safety analysis for the HPSI and LPSI pumps. This analysis establishes the flow and discharge head requirements at the design point for the HPSI pump.

Question 19

When is Core Heat removal satisfied?

Answer 19

Core Heat Removal is being satisfied if T_H and the Average of Qualified CETs temperatures are less than superheated.

Any degree of core uncovery for any period of time indicates an advanced phase in
approach to inadequate core cooling. If the core is uncovered, core exit temperatures will rapidly increase to the superheated range.

Question 20

When is PCS Heat Removal Satisfied?

Answer 20

The PCS Heat Removal Safety Function is satisfied if the following conditions exist:

• At least one S/G has level being maintained between 60% and 70% [normal control band] with feedwater available or S/G level is greater than -84% [minimum level for heat removal] and is restoring to between 60% and 70% [normal control band].
• PCS T_Cs are stable or lowering.

The preferred S/G level band is based on the S/G level normally maintained between hot standby and 100% Reactor power which assures the entire S/G tube bundle is covered.

The less desirable but acceptable criterion of level greater than -84% [minimum level for heat removal] and restoring to between 60% and 70% [normal control band] is broad enough to ensure that at least one third of a S/G’s tubes are covered to facilitate natural circulation in the PCS. If level is rising to the desired level band, then AFW flow is sufficient for removing the existing PCS heat load.
T_Cs stable or lowering implies that S/Gs and once-through-cooling or available S/Gs alone are adequately removing decay heat.

Question 21

What is the basis of Condition 1 for calling Containment Isolations satisfied?

Answer 21

Condition 1 is satisfied if:

• Containment pressure is less than 4.0 psig [CIAS setpoint] as read on PIA-1814 and PIA-1815. Containment pressure less than 4.0 psig [CIAS setpoint] would be indicative of an event outside of the Containment. In this condition, the Containment does not require isolation due to high pressure.
• Containment Area Monitors indicate no unexplained rise in activity and alarms are clear. This criterion verifies that there are no [containment area radiation monitor greater than the alarm setpoint] or unexplained rises (as would be the case with an inter-system LOCA).
• Condenser Off Gas Monitor RIA-0631 indicates no unexplained rise in activity and the alarm is clear. This criterion is used as a diagnostic to verify that a SGTR is NOT also occurring. An unexplained rise in steam plant activity, or if alarms are present, would be indicative of an SGTR.
• Steam Line Monitors indicate no unexplained rise in activity and alarms are clear. This criterion is used as a diagnostic to verify that a SGTR is NOT also occurring. An unexplained rise in steam plant activity, or if alarms are present, would be indicative of an SGTR.

Question 22

What is the basis for Condition 2 acceptance criteria for Containment Isolation?

Answer 22

Condition 2 is satisfied if:

• Condenser Off Gas Monitor RIA-0631 indicates no unexplained rise in activity and the alarm is clear. This criterion is used as a diagnostic to verify that a SGTR is NOT also occurring. An unexplained rise in steam plant activity, or if alarms are present, would be indicative of an SGTR.
• Main Steam Line Monitors indicate no unexplained rise in activity and alarms are clear. This criterion is used as a diagnostic to verify that a SGTR is NOT also occurring. An unexplained rise in steam plant activity, or if alarms are present, would be indicative of an SGTR.
• Containment Isolation Signal initiated (“CIS INITIATED” (EK-1126) alarmed). If CIAS is present, then Containment isolation is satisfied if no steam plant activity monitor is alarming or has no unexplained rise in activity. These criteria ensure that the Containment is isolated when necessary (greater than the CIAS setpoint) and that a SGTR is considered when performing Diagnostic Actions if steam plant radiation alarms are obtained.

Question 23

What is Condition 1 that satisfies the Containment Atmosphere Safety Function check?

Answer 23

Condition 1:

• Containment temperature less than 225F is the saturated temperature for Containment Spray actuation setpoint. This will verify parameters are maintained below Containment Spray actuation setpoint.
• Containment pressure is less than 4.0 psig [CSAS setpoint] as read on PIA-1814 and PIA-1815. Containment pressure lower than the CHP setpoint indicates that the LOCA is a small break or that the LOCA is outside the Containment. High Containment pressure or higher than normal Containment temperature are indications that a possible high energy line break in the Containment has occurred. The intent of this step is to alert the operator to the potential for a high energy line break and to prompt further evaluation of instantaneous Containment pressure changes.
• Containment hydrogen concentration less than 1% [minimum detectable concentration] and Containment hydrogen less than 3% [lower flammability concentration]. 1% [minimum detectable concentration] is the alarm setpoint on the Hydrogen monitors and is considered here as the lowest detectable level. The Containment conditions make it unlikely that a mechanism exists for increasing Containment Hydrogen concentration. Hydrogen can be generated and released to the Containment Atmosphere by mechanisms like metal-water reactions, corrosion reactions and radiolytic decomposition of water during LOCA events. Maintaining hydrogen less than 3% [lower flammability concentration] ensures the Containment hydrogen concentration remains below the lower flammable concentration following a DBA.
• Containment water level is less than 596’ 7.5”. {Highest expected containment flood level}. Containment {Highest expected containment flood level} 596’ 7.5” ensures that a service water leak is not contributing to Containment flood level, jeopardizing necessary equipment. If Service Water is not necessary to maintain the safety function, then the Service Water to Containment should be isolated to ensure that a Service Water leak is not contributing to Containment Sump level, jeopardizing necessary equipment.

Question 24

What is Condition 2 that satisfies the Containment Atmosphere Safety Function check?

Answer 24

• Containment pressure is less than 70 psia [containment design pressure]. This is the limiting pressure assumed in the accident analysis for high energy line releases inside Containment.
• Per tables of two configurations, both of the listed configurations require at least one Containment Spray pump in operation in parallel with one of two other sub-configurations (ie, the other Spray pump or three Containment Air Coolers). Spray flow shall be within the containment spray header [design flow rate]. The requirement for use of at least one Air Cooler fan in the accident mode is to provide for mixing. An assumption in the FSAR accident analysis Chapter 14.22 is that the air cooler fans are running to prevent pockets of hydrogen from forming. Therefore, the Safety Function Status Check ensures that at least one fan is operating. Ideally all fans should be run to provide uniform mixing.
• Containment hydrogen concentration less than 1% [minimum detectable
  concentration] and Containment hydrogen less than 3% [lower flammability concentration].
• Containment water level is less than 596’ 7.5”. {Highest expected containment flood level}. Containment {Highest expected containment flood level} 596’ 7.5” ensures that a service water leak is not contributing to Containment flood level, jeopardizing necessary equipment.

Question 25

How does MVAW impact MVAE?

Answer 25

Following a large break LOCA with a loss of offsite power, the Service Water header pressures must be kept above the minimum pressures necessary to supply critical Service Water components with sufficient flow - 36 psig.

When the SW Pumps are being powered by the D/Gs, the potential exists for the Service Water Pumps to operate at flowrates greater than those assumed in the D/G load study.

D/G load must be monitored to ensure an undesirable overload does not occur.
FSAR Section 9.1.2.3 expectations of Service Water capabilities for a LOCA are that one or two Service Water pumps will be in operation supplying, as a minimum, the critical Service Water header for operating Emergency Diesel Generators and Air Compressors.

Question 26

What is the basis of the MVAA status check?

Answer 26

At least one Instrument Air Compressor should remain energized to supply Instrument Air pressure for control of equipment. Instrument Air pressure above the {minimum air pressure for reliable control valve operation} ensures the continued ability to perform remote operation of equipment required for optimal safety function success paths (Atmospheric Steam Dump Valves, Auxiliary Feedwater Valves, Condensate Pump Recirculation Valves, Letdown orifices, etc).

Question 27

Why is a H2 monitor place in service in accident mode? How long does it take to get a sample?

Answer 27

Since the Hydrogen Monitor is only placed in service at times when the potential exists for degraded Containment conditions, the step directs the use of key switch that prevents the Containment Isolation Valves from closing or allows them to open with a Containment Isolation signal present. The use of this switch prevents potential damage to the monitor sample pumps from inadvertent closure of the Containment Isolation valves.

15 minutes

Question 28

What is the criteria for reducing containment spray?

Answer 28

Reducing Containment Spray

• RAS has NOT actuated
• Containment Pressure less than 33 psia
• CACs in Accident Mode
• SIS Actuated with flow within the requirements of EOP Supplement 4

If three pumps operating, then stop either P-54B or P-54C

If two pumps operating, then close one containment spray valve. CV-3001 preferred.

Stop one of the spray pumps - not P-54A

Verify Containment Pressure less than 70 psia.

Question 29

What is the criteria for stopping the last containment spray pump?

Answer 29

• Containment pressure less than 3 psig
• Containment Spray NOT required for
  
  • Containment Ambient Cooling
  • HPSI subcooling
  • Iodine removal via Chemistry approval or
    
    • High Range Gamma less than 1800 R/Hr
    • Containment Isolated per EOP Supplement 6
    • Less than 1-hour elasped since reactor trip.