Blackout Flashcards
What cooling process ultimately required PVGS to adopt a 16 hr coping strategy for a blackout?
two phase natural circulation, which leads to RCS superheat conditions if not mitigated.
State the major mitigation strategy associated with a blackout. welch version
- Addresses Loss of all AC (PBA/PBB de-energized) and ELAP events (Extended Loss of AC Power)
- Ensures RCS heat removal using AFA and ADVs (does not require AC power)
- All other safety functions are monitored throughout the EOP. includes use of AFA.
- Restores electrical power.
- If Offsite or DG not expected to be restore within 1 hour, SBOG is used to energize PBA-S03.
- Copes with SBO for 16 hours, by which time either offsite power or a DG should be restored.
- Ensures the plant is coping with the loss of power. includes maintaining RCS subcooling.
- Maintain RCS subcooling by performing a limited, controlled cooldown. (maintains single phase natural circulation)
- If Offsite or DG not expected to be restored within 4 hours: cooldown to SDC entry conditions is started.
- If Offsite or DG not expected to be restored within 8 hours:
- SFP Cooling is restored.
- Supplemental N2 Bottles are aligned to supply ADVs (or if ADV accumulator low pressure alarm received)
- Restore enough electrical capacity to allow transition to LOOP EOP or another appropriate procedure as directed by TSC.
State the major mitigation strategies associated with a blackout.
- Ensure maintenance of safety functions which do not rely on AC power.
- includes the use of AFA and ADVs for heat removal.
- Restore electrical power.
- BO coping strategy supports using SBOG for 16 hrs, at which time DG or offsite should be back.
- If SBOG cant be started within 1 hr, EDG and offsite not available following SBOG, an ELAP is declared and FLEX is used in parallel.
- FLEX focus is to cool rx to a stable Tcold but still high enough for SGs to produce steam to run AFA and low enough so that one CHP capacity is greater than RCP seal leakoff. RCS cooldown and depress reduces inventory loss.
- Class batteries are extended with a DC load shed to last past the time the 480V portable DGs are aligned to supply power. FLEX has no sequiencing.
- Ensure the plant is coping with the loss of power. Includes maintaining RCS Subcooling by performing a limited controlled cooldown.
- If power not expected back within 4 hours, BO coping strategy will cooldown to SDC.
- If power not expected to be restored within 8 hrs, BO directs SFP cooling restored.
- Align ADV actuators with supplemental N2 bottles within 8 hours or if ATM Accum press LO alarm comes in.
- Restore enough power to allow for transition to either LOOP or another appropriate ORP/FRP.
What is the blackout coping strategy discussed in the BO orp?
General approach is to maintain heat removal from core by natural circulation.
- The SBOG will be used to energize PBA-S03 within ONE hour of a BO.
- PBA-S03 is chosen so that PKA has DC power supplied from a class battery charger and can power the AFA and A train ADVs
- Required loads like CHPs, Class MCCs, PZR htrs, SP, EW, EC, CREFS, and SWGR AFUs are energized.
- Contingency actions provide guidance for another unit’s DG to supply power. Used when you can’t restore power within ONE hour from own EDG, offsite or SGOB.
What combination of loads can a single SBOG supply power to?
A single SBOG can supply power to:
PBA-S03 coping loads, AFA and one CHP.
PBA-S03 coping loads, AFN and one CHP.
PBA-S03 coping loads, and HPSI A.
What combination of loads can two SBOGs in parallel supply power to?
Two SBOGs in parallel to PBA-S03:
AFN, E CH Pump, A HPSI, and PBA-S03 coping loads (~ 4163 KW on SBOGs)
What procedure method is required to parallel two SBOGs and why?
Paralleling of SBOGs requires 50.54x/y to be invoked (Should work, but it NOT tested)
With LTOP in service, and a blackout occurs, should you enter the BO orp?
NO. use lower mode functional.
What are the exit criteria from the BO orp, besides the obvious transition to the FRP?
BO SFSC not satisfied AND ELAP not in progress(you could have a ELAP and not meet SFSCs and still stay in BO)
BO has accomplished its purpose by satsifying the following:
- At least one vital 4.16 kV bus is energized from (Offsite Power OR any DG) [not from an SBOG]
- Transition to LOOP EOP or GOP if SDC entry criteria is met.
- All SFSCs are met
- An appropriate procedure to implement has been provided and administratively approved.
Why is an MSIS initiated during a BO?
Prevents overpressurizing the Condenser on a loss of CW.
Why are all CHPs placed in PTL on a BO?
CHPs and Seal Inj are lost and restoration will need to be controlled in order to minimize the possibility of RCP seal damage.
How is the step to maintain subcooling performed during a blackout?
- Cooldown as needed to maintain subcooling 24-50°F [44-50°F].
- Maintain 50°F max subcooling.
- If subcooling cannot be maintained ≥ 24°F [44%]:
- Maintain one SG 45-60% NR level
- Monitor REP CET < 44°F [60°F] superheated and NOT ↑
- Hot standby should be able to maintained for 4 hours on a SBO, assuming minimal RCS leakage.
Once SCM is < 50°F (due to pressure slowly ↓), maintain < 50°F SCM to minimize RCS leakage. Maintains RCS inventory and single phase natural circ as long as possible.
Eventually reflux boiling could occur. This will keep the core cooled (less efficiently). Maintain SGWL and monitor core fore superheat conditions.
What action is necessary to maintain subcooling margin during a blackout?
During the 4 hour initial time period, SCM will slowly lower due to pressure lowering from no heaters. Once in the band of 24F - 50F SCM perform a deliberate cooldown to maintain this band.
It is not necessary to lower pressure initially to get to this range.
This strategy maintains single phase natural circ for as long as possible. Simplifies control and minimizes reliance of reflux boiling for core cooling. Should 2 phase NC cooling need to occur, ensure REPCET is constant or lowering and less than 44F[60F] superheat.
RCS should be cooled by feeding one SG with AFA and steaming with ADVs. If cooldown is performed with minimal Lpzr, SCM will not be maintained. This condition coupled with a loss of inventory can rapidly depressurize the plant, resulting in a loss of SCM.
How is reactivity controlled during a blackout?
At 50F Tcold intervals check that the rx will remain shutdown by > 1%dK/K or more for Tcold 50F less than indicated Tcold and boron concentration at the time of event initiation.
CEAs will give more than required SDM. However, until SITs discharge to RCS there is no way to control reactivity changes other than controlling the cooldown. This SDM determination is the only way to identify if the cooldown will challenge Rx Control SFSC.
If adequate SDM does NOT exist, can the cooldown continue?
YES, provided that the Rx control SFSC are met.
