Loss of CH or LD

Question 1

Explain the flowpath and mitigation strategies of loss of CH or LD.

To include Trip criteria, charging availability, and extended loss of letdown actions.

Answer 1

• Trip criteria
  
  • Lpzr < 33% and charging restoration not impending.
• Charging availability
  
  • Evaluate need to secure all charging
  • Evaluate gas binding
  • Evaluate charging line rupture
  • Evaluate charging path availability.
• Extended loss of letdown
  
  • Initiate downpower low in Lpzr band
  • Maintain Tave low in band
  • Maximize CEA insertion while controlling ASI
  • Maximizing boration while CHPs are running

Question 2

How does the mitigation strategy differ significantly if the unit is in Mode 3, 4 or 5 with a loss of CH or LD?

Answer 2

The major difference is with a solid plant configuration.

Actions include isolating seal bleedoff

Stopping all CHPs

Opening CHE-240

Closing LD and BPCVs

Operating CHPs to control RCS pressure.

Question 3

How is the temperature interlock of CHB-515 able to be overridden in order to restore letdown on a temp fault?

Answer 3

CHB-515 will isolate LD on >413F RHX outlet temp. If this is due to a faulty temp insturment, maintenance will install a jumper to override the temp interlock.

This can only be done if CHN-TI-221 indication is available. Operator action is required to protect the LD line.

Question 4

How is the temperature interlock of CHB-523 overridden following a faulty temp instrument?

Answer 4

CHB-523 will close > 135F.

If CHN-TS-224 has failed, and letdown is desired, take the switch to OPEN to override the hit temp signal. If this does not work then maintenance can override by installing a jumper.

Question 5

Describe the major actions for restoring letdown with a bubble in the pressurizer.

Answer 5

Monitor RHX outlet temp and LD backpressure.

Set BPCV to man and 60%

Isolate Seal Inj and start one CHP.

If LD lost for > 22min and RCS is > 130F, then warmup LD line

Adj LDCV and BPCVs to estblish 25-30 gpm and 220-400psig.

PLCS in Man and start additional CHP. Adj LD and BPCVs to set desired Lpzr.

Place controllers in auto. Restore Seal Inj.

Question 6

How does restoration of LD during solid plant conditions differ from a bubble inthe Pzr?

Answer 6

When LD is established BPCVs are throttled to control RCS pressure with running CHPs.

Question 7

Explain how to restore Seal Inj following a loss of CH.

Answer 7

Ensure indiv Seal Inj control valves are closed(reverse acting so 100%demand is closed)

Ensure CHP-255 is open

Ensure Seal Inj HX isolation is open.

Adj to 6.5 -7.0 per RCP

Place controllers in auto

Place CHE-240 in auto

Consider restoring CBO if Seal Inj and NC flow > 450gom.

Question 8

What is the major strategy for operating with extended loss of letdown?

Answer 8

• Boron equalization should be minimized since it depletes RCS hydrogen.
• Stop all charging pumps and isolate seal injection if approaching 56% LPZR
• Seal bleedoff will lower LPZR ~10% in 55 minutes. (3 gpm bleedoff per RCP and ~66 gal/% in PZR)
• Operate charging as needed to maintain LPZR 33-53%
• Seal Injection can be restored if needed
• Drain VCT locally if needed to reduce level

Question 9

Explain how gas binding of CHPs is mitigated.

Answer 9

Evaluate for Charging Pump gas binding (should use multiple indications)

• Charging header flow / pressure fluctuations
• Charging header flow less than expected for running charging pumps
• Charging suction source (VCT, RWT) level lost
• If charging flow is < 40 gpm, isolate letdown and PTL charging pumps
  
  • If due to loss of VCT level, vent to the vent receiver
  • If not due to VCT level, vent to the recycle drain header
• If flow is > 40 gpm, determine which pump is gas bound
  
  • With two pumps operating while one of the pumps is gas bound, the primary indication of the gas bound pump will be the sound. A pump that is partly gas bound will initially have much louder cavitation noises than a filled pump. As the pump becomes fully gas bound, the plate valves will make much less noise than those in a pump that is filled with fluid.
  • PTL and locally isolate the affected pump

Question 10

How is a CH line rupture mitigated?

Answer 10

Charging line rupture:

• Isolate letdown
• PTL all charging pumps
• Close VCT outlet (CHN-501) [hold HS in close until AO opens the breaker]

If flow cannot be restored through the normal path, align thru HPSI Cold Leg Injection via SIE-V508. (App. J)

• Aligns charging to the A HPSI cold leg injection header (A HPSI is inoperable)
• A or B LPSI is inoperable if a HPSI A Injection Valve is opened with injection header pressure > 1525 psig.
• If charging suction not aligned to the RWT, SI header boron will lower below 4000 ppm and impact ECCS operability.

Restore letdown once charging flow is available / restored