LOAF Flashcards
Describe the safety analysis assumptions for TAA - Decrease in HR
All assumptions based on maximizing RCS pressure.
No credible failures to MSSVs or PSVs; credit not taken for non class control systems.
The limiting event is LOCV - loss of condenser vacuum, however a FWLB with a LOOP and one fast bus transfer fails, this is the most limiting with respec to long term RCS heat removal.
State the most limiting event for a decrease in heat removal.
The limiting event is LOCV - loss of condenser vacuum, however a FWLB with a LOOP and one fast bus transfer fails, this is the most limiting with respec to long term RCS heat removal.
What assumptions are made regarding the management of safety functions in decreased heat removal safety analysis?
Pressure and inventory control are impacted.
PSVs open with a max pressure of 2745psia(<110% of design press)
Heat removal impacted
3 banks of MSSVs open with a max Ps/g of 1390psia(<1110% of secondary design of 1270psia)
What are the major mitigating strategies for a LOAF?
Mitigating Strategy:
Stop RCPs to limit heat input (conserves SG inventory) (~19 MWth)
Isolating SG liquid outputs to conserve SG inventory.
Restore feed flow to at least one SG.
Evaluate cooling down to SDC entry or staying in hot standby.
Determine the RCS response as SG dryout occurs during a LOAF
Steam Generator Dryout
- EOPs consider a SG to be dry when level is below 0% Wide Range (below any MCR indication).
- 0% Wide Range: ~ 1/3 of the tubes remain covered, which is ~ 20 minutes of remaining heat removal capability
- When SG reaches actual dryout conditions: SG pressure will begin to decay rapidly
- Loop ΔT ↓ as Tcold ↑ towards Thot.
- At this point, the affected SG is no longer providing cooling (DHR)
- When both SGs reach dryout:
- RCS temps / pressure ↑
- RCS subcooling ↓
- Core uncovery could occur within 1 hour of loss of feed water / dryout.
State the sources of feedwater available during a LOAF.
MFPs:
- Must have CDP operating,
- steam supply(MSIS would need to be overridden),
- Cond vacuum
- MFP lube oil pump power
- Discharge flowpath with IA and/or power.
AFN-P01
- Power to PBA-S03 and either PKA-D21(normal) or A batt charger outlet(alt.)
- 480VAC class power to CST suction valves
- Feed path through downcomer isolations and either bypass or control valves
AFA-P01
- intact suction source(CST or RMWT)
- Steam source(not isolated by MSIS)
- intact discharge flowpath(NOT thru downcomer valves)
- PKA and PKC if operated from CR.
AFB-P01
- Power to PPB-S04
- control pwer from PKB-D22
- CST or RMWT
- Intact disch path
CDPs
- 4.16kv non vital bus pwr
- feed path thru the downcomer
Fire pump
- SA 118 xconn FP with AF
How are RCPs operated during a LOAF. include a discussion on bases for these steps
All RCPs are tripped for a LOAF. The basis for this action is to remove a considerable amount of heat input from the RCPs into the RCS.
RCP restart is addressed later in the ORP.
What is the guidance for restoring feedwater during a LOAF and what Ls/g satisfies requirements of the LOAF ORP?
Feedwater restoration:
- If one or both SGs have dried out, only one SG is chosen for feeding.
- If only one has dried out, the one with inventory is the one to be fed.
- If both dry out, then pick one to feed; one criteria might be to pick the last one to dry out, if no other reasons exist to choose one over the other
Guidance is to restore and maintain at least one SG to 45-60%NR.
The basis for this is to ensure the ability to remove heat from the RCS is not challenged. Additionally, it ensure that the MSIS setpoint is not challenged.
How should selection of the SG to be fed be considered?
State the max feed rates for each feed source.
If only one has dried out, the one with inventory is the one to be fed.
Max feed flow following dryout:
- AFA/AFB ≤1000 gpm.
- MFW/AFN ≤0.5 E6 lbm/hr (~ 1000 gpm).
- Reduces the risk of damage due to stresses on a dry SG imposed by introduction of cold feed water.
If a LOOP has occurred and AFA or AFB are available, the use of AFN should be delayed until MFW piping has been slowly re-pressurized with the condensate pumps, or it has been allowed sufficient time to cool, to minimize the potential for a water hammer event.
If both SGs have experienced dryout, how long does it take unitl core uncovery begins to occur?
Core uncovery can occur in under 1 hr.
How should a rising Lpzr be addressed during a LOAF condition?
IF BOTH: Lpzr > 65% and LD is not aligned, THEN
if cooling water being supplied to RCP seals AND CHPs are not being used for reactivity control then STOP all CHPs.
If following this action, seal outlet temperatures approach 250F on stby RCPs, then isolate controlled bleedoff from affected seals.
IF ANY of the following: Cooling water is NOT being supplied to the RCP seals or CHPs are being used for reactivity control THEN:
Cooldown the RCS.
State the SFSC for Reactivity control as it pertains to a LOAF
Reactivity Control
Reactor power ↓ or < 2x10-4% and stable or ↓
All FSCEAs inserted or borating > 40 gpm or adequate SDM established
State the SFSCs for MVA as it pertains to LOAF.
Maintenance of Vital Auxiliaries
- At least one vital 4.16 kV bus energized.
- At least one train of PK and PN is available and is on the same train as the powered vital AC bus.
- PKA-M41, PKC-M43, and PNA-D25
- PKB-M42, PKD-M44, and PNB-D26
- No jeopardized safety functions require restoration of electrical power to a vital AC or DC bus. (bus plus)
State the SFSCs for RCS inventory control as it pertains to LOAF
RCS Inventory Control
- LPZR 10 - 65%
- RCS is ≥ 24°F subcooled.
- RVUH level ≥ 16%
State the SFSCs for RCS Pressure control as it pertains to LOAF
RCS Pressure Control
- PPZR is within the P/T limits (App. 2)
