AOP-1 Loss of Load

Question 1

What is AOP-1?

Answer 1

It is the loss of load event.

Initiated by:

• Loss of external electrical load

or

• Turbine Trip

AOP-1 mitigates

• Challenges to the acceptance criteria for both primary and secondary system pressurization and DNBR.

Question 2

What happens during a loss of load, without reactor trip?

Answer 2

Primary system temperatures increase due to an increase in the secondary side temperature. Results in coolant expanding into the pressurizer causing an increase in the pressurizer pressure.

Primary side is protected by pressurizer safety valves.

Secondary side is protected by code safties.

Question 3

What assumptions are in the FSAR Analysis for loss of load?

Answer 3

FSAR Analysis

A steam generator tube plugging level of 25%

Initial indicated pressurizer level of 67.8% (Alarm setpoint of 62.8% plus 5% for instrument uncertainty.

Question 4

What are the symptoms of a loss of load?

Answer 4

Symptoms

Pressurizer Pressure and Level Rising

Question 5

What are the AOP-1 Entry Conditions?

Answer 5

Symptoms of a Loss of Load (eg, Pressurizer pressure rising, Pressurizer level rising) in conjunction with any of the following:

• EK-0968, “LOOP 1 TAVE/TREF GROSS DEVIATION” (5F)
• EK-0969, “LOOP 2 TAVE/TREF GROSS DEVIATION” (5F)
• Turbine Control Valve Malfunction (close)

Question 6

What are the reactor and turbine trip criteria of AOP-1?

Answer 6

Reactor Trip

• Reactor Power greater than or equal to 15% AND Turbine Governor Valve control in manual and not controlling

Turbine Trip

• Reactor Power less than 15% AND Turbine Governor Valve control in manual and not controlling

Question 7

What are the actions of a turbine governor valve control problem?

Answer 7

VERIFY Turbine Governor Valve control operating properly.

If NOT THEN, PLACE Turbine Controls to MANUAL.

Question 8

If turbine valve control is lost due to EHC pressure failure, what do you do?

Answer 8

EHC Failure

• If it is determined that Turbine valves are repositioning due to loss of EHC pressure (because an EHC Pump is not operating), then the EHC Pump should NOT be manually started since starting an EHC Pump under these conditions will cause the Turbine valves to reposition to their original position and thereby cause a significant transient on the Main Turbine.

Question 9

What do you do on Main Turbine Stop Valve Partial Closure?

Answer 9

Main Turbine Stop Valve Partial Closure

• REMOVE affected Stop Valve from the steam path in less than 2 hours:
• REDUCE Reactor power to between 84% and 86 %.
• CLOSE affected Stop Valve:
  
  • Utilizes valve test of SOP-8
  • After the Governor Valve is closed, the DEH Controller will output a five-second signal to close the selected Stop Valve then a five-second reopen signal.
  • PRESS P6, “Hold Valve Test,” when SV closed and isolate EHC to affected stop valve.

Question 10

A power reduction to between 84% and 86% RTP is required for a partially failed closed stop valve. What do you do if the valve reopens during the down power?

Answer 10

The power reduction may be terminated. An engineering evaluation
is needed before raising power.

Question 11

What do you do if a spurious MSR Inlet Closure occurs and why?

Answer 11

MSR Inlet Closure

CLOSE the manual isolation to the affected MSR Tube Bundle Inlet control valve.

Prevents damage to the tube bundles should the control valve(s) start cycling open and closed

Question 12

How long can you operate with an MSR Tube Bundle Isolated and why?

Answer 12

MSR Tube Bundle Isolated

Should be limited to 7 days.

• Affects the erosion rate of the LP Turbine Rotor blades
• May cause differential cooling of the rotor blades
• Will likely cause vibration changes

Question 13

What do you do if a Reheat Stop or Intercept Stop valve spuriously closes?

Answer 13

Reheat Stop or Intercept Stop

• PRESS Reset pushbutton on panel EC-O1, Turbine Generator Control Console, to close all MSR Reheat Steam Supply Valves.
• ISOLATE EHC fluid to the Reheat Stop and Intercept Valve on the affected MSRs by closing the applicable EHC Oil Supply Valve
• LOWER turbine load such that Reactor Power is less than 50% (higher of NI,
  Delta T, or Heat Balance Power)

Question 14

How long do you have to perform the downpower for isolating an MSR?

Answer 14

LOWER turbine load such that Reactor Power is less than 50 % (higher of NI,
Delta T, or Heat Balance Power) within approximately 3 hours.

The 3-hour time period provides 1 hour for preparation and 2 hours for a derate at
25%/hour. Operation may continue for 80 hours at reduced load.

Question 15

How long can you operate at 50% power with the MSR’s isolated to due to a spurious Reheat Stop or Intercept Stop valve closure?

Answer 15

IF 80 hours of operation at reduced power has elapsed and the malfunction has
NOT been corrected, THEN REMOVE unit from service

Question 16

When do you trip the reactor or turbine for a failed closed Reheat Stop or Intercept Stop valve?

Answer 16

IF any of the following conditions occur, THEN TRIP reactor/turbine:

• Turbine metal or bearing temperatures reach trip limits
• Turbine vibration reaches trip limits
• The Reheat Stop or Intercept valves from both of the MSRs feeding the same LP Turbine section close

Question 17

What is the mitigation strategy for loss of load, AOP-1?

Answer 17

• Add reactivity (borating and/or insert control rods) to maintain T_AVE +-3F of T_REF
• Ensure systems are responding to stabilize plant conditions.

Question 18

What happens to T_ave under loss of load conditions and how to you mitigate it?

Answer 18

T_ave rises as heat removal by the secondary side stops.

Insert rods/and or borate to maintain within +-3F of T_ref

Question 19

Why are two forms of reactivity addition allowed during AOP-1?

Answer 19

EN-OP-115, “Conduct of Operations,” provide restrictions for positive reactivity changes but does not prohibit using both methods for negative reactivity changes.

“Positive reactivity additions are performed using one method at a time unless, for
PWRs only, in accordance with an approved procedure or reactivity plan.”

Question 20

What are the Stable Parameters for concluding AOP-1?

Answer 20

Stable Parameters

• Pressurizer Level Control System. (42% - 57%)
• Pressurizer Pressure Control System. (2010 psia - 2100 psia)
• Steam Generator Level Control System. (60% - 70%)

Also,

VERIFY Pressurizer pressure maintained less than or equal to 2100 psia.

VERIFY Pressurizer level maintained less than 62.8%.

Question 21

What Tech Specs are associated with AOP-1?

Answer 21

T.S. 3.4.9

• In Mode 1, 2 and 3 the pressurizer shall be OPERABLE with:
• a. Pressurizer water level < 62.8%;
• b. ≥ 375 kW of pressurizer heater capacity available from electrical bus 1D, and
• c. ≥ 375 kW of pressurizer heater capacity available from electrical bus 1E with the capability of being powered from an emergency power supply.

T.S. 3.4.1, “PCS Pressure, Temperature, and Flow Departure from Nucleate Boiling
(DNB) Limits.” shall be per COLR in Mode 1.

T.S. 3.4.16 SR 3.4.16.2

• Verify primary coolant DOSE EQUIVALENT I-131 specific activity ≤ 1.0 μCi/gm.
• Every 14 hours AND Once between 2 and 6 hours after THERMAL POWER change of ≥ 15% RTP within a 1 hour period