AP 20 Flashcards
Purpose: The purpose of this procedure is to ensure proper response in the event of a loss of nuclear service water, to assess plant conditions, and identify the appropriate steps for the following cases
AP-20 Loss of RN
Symptoms of? •"A RN PMP DISCHARGE LO PRESS" alarm •"B RN PMP DISCHARGE LO PRESS" alarm •"A RN PUMP ABNORMAL FLO" alarm •"B RN PUMP ABNORMAL FLO" alarm •RN Non-Essential Header pressure low •RN Pump tripped •Indications of significant RN pump cavitation •Entry into this AP specified by another procedure
Case I Loss of Operating RN Train
Symptoms of?
•”A RN PMP SUCTION LO PRESS” alarm
•”B RN PMP SUCTION LO PRESS” alarm
•”A RN PMP DISCHARGE LO PRESS” alarm
•”B RN PMP DISCHARGE LO PRESS” alarm
•1A RN Pump amps indicate low
•1B RN Pump amps indicate low
•Visual observation of Cowans Ford Dam failure with potential loss of LLI
•Notification from plant personnel of potential loss of LLI.
•Entry into this AP specified by another procedure
Case II Loss of LLI or RC Supply Crossover
No immediate actions
Time Critical actions: AP 20
Case II steps 1-18 time critical (< 60 Min) > Pond Depletion
What are the pump temperature limits without RN cooling:
NV, KC, NCP?
NV (190 F pump bearings) / (200 F motor bearings) Enclosure 10actions
KC (200 F motor bearings) / (240 F motor stator) Enclosure 11 actions
NCP normal trip criteria of 311 F stator temp applies
•Check if cavitation is occurring.
•Check VI header press low. (low VI press > failed open throttle valves)
o Attempt to stop cavitation by aligning B train to the pond. If cavitation stops continue alignment of B train to the pond.
•If cavitation > if seismic event non-seismic piping isol. If cavitation continues, could be due to clogged strainer. > direction is to swap trains.
( Note : Pumps not tripped on cavitation caused by high flow rates)
oPlace idle train in service. If venting req’d> stop pump, vent and restart.
•Start opposite units RN pumps (Both trains)> maximizes the opposite unit’s RN pressure will maximize the x-tie between the units via the RL tie downstream of each unit’s RN-42.
•Establish RV backflow if neither train not available to start.
o Isolate RN components not required.
6900V swgr AHU’s isolated
Jockey pumps >man/ off (no suction flow path)
o Reduce heat loads
Letdown reduced to 45 gpm (largest KC load)
Monitor NV/ KC pumps’ brg and stator temps
• NV pumps swapped as necessary, including running the PD pump if available, when stator or pump temps reach limits
• Gravity drains (RN to floor) aligned to NV/ KC pumps if req’d
• IF NV pump brg temp increases and can’t be stabilized, the standby m/u pump is started and NV pump secured > letdown is isolated.
• No RV pump available and no RN pump on applicable unit & both RN pumps available on ‘donor’ unit TSC DIRECTION ONLY:
oManual RN cross-tie valves between units opened, after ensuring U2 will not enter TS 3.0.3 when cross-ties
Case I Strategy
•Establish suction flow from SNSWP (either unit)
•If loss of dam, due to earthquake >isolate non-seismic piping
o Monitor for air binding. if air binding occurs:
o See if aligning to pond stopped cavitation.
Stopped: then continue aligning B train to pond.
Continuing: Secure DG (emerg stop) and CA pumps(depress start/ stop simultaneously, to prevent re-start. (no cooling)
o Secure affected RN pump
o Swap power supplies to 1(2) EMXH as needed to supply shared RN valves.
Note: Stop air-bound pumps to vent and restart. Do not stop pumps cavitating, due to high flow.
•If neither unit can start an RN pump transfer to case I (higher priority) When an RN pump can be started return to case II
•Minimize pond depletion for long term operation
o Isolate RN to RL header (man/off on Jockey pumps, due to no suction source)
• When RN restored:
o Re-align equipment supplied by RN or swap operating trains
o If ND running use AP-19 to restore
Note: Procedure is time critical and only one unit needs to perform case II.
Case II Strategy
RN pumps do not behave normally, they will self correct flow to adjust for reduced NPSH
Per engineering, check RN discharge pressure. If it is less than the lo alarm (50psig) then assume load demands are excessive
• Do not trip cavitating RN pump (per engineering)
• It has been determined that the RN pumps can provide sufficient flow even while cavitating
• Potential events:
o Loss of VI
All 4 RN pumps running on LLI with lots of valves failed open
o Seismic event
Non-seismic header downstream of RN-42A will add load to RN pumps
o LOOP with failure of B train swap to pond
All 4 RN pumps running on LLI with lots of valves failed open
• Throttle RN to KC HX
• Aligning one train to pond should alleviate the problem
o RN cavitation
Max ‘suggested’ set points from engineering
o 16000gpm (any pump/train) from LLI
o 11500 A train pumps from pond
o 13000 B train pumps from pond
• Operation above these set points is a long term impellor wear issue not an immediate concern
• Under abnormal/emergency conditions these limits may be exceeded
o RN flow
Control room temp
As long as the enclosure to try to start the chiller is started within 30 min, temps should not exceed limits
SNSWP draw down
If one train is aligned to the pond and the other to LLI with the crossties open, water from the pond could go through the crossties and discharge out of RC
Starting the opposite units RN pumps
Both running will allow more RV flow to go to the unit that lost RN due to increased header pressure on the unit with running RN
RV backflow limits
RV (~3000gpm per pump) should be sufficient to supply RN header to maintain hot standby conditions (per RV/RN flow analysis)
• If non-essential loads isolated
ND in RHR
KC outlet flow valves will both be full open (RN discharge flow = 0)
Operator has to manually control inlet valve
KC heat removal
While operating, letdown is largest load on KC
While shutdown, ND largest load on KC
• If NCP’s were running, SG’s should be available for cooling
o If in mode 5, heatup to mode 4 will occur if using SG to cool NCS
• If NCP’s were not running, good chance NCS not intact
o RV to RN back feed very high priority in this case
Loss of NV pumps
Might need to run standby makeup pump if they have overheated and had to be shutdown
•If seals already over 225 degrees, standby makeup pump is not started
NV pumps will approach its operating limit in ~15 min
• Then start idle pump since its bearings are at ambient
o Run for ~30 min
• Then swap to PD pump
o Run for ~30 min
• If RN not restored, gravity drain to cool original NV pump and run it
o If that will not keep NV pump cool, standby makeup pump run
Loss of KC pumps
Will run for ~50-60 min prior to overheating
Can swap between each train up to 5 times before running into starting current limits
Will reach 311 degree trip point in ~20 min
If RX trip required, TDCAP started as it does not require RN
Before going to E-0, another operator continues in this AP as the EP relies on a lot of the equipment down due to RN
• Highest priority to restoration of NCP seals and RN
NCP’s
May be used to align the opposite units RN to the unit with failed RN
Both RN pumps running on the other unit
Opening the crossties making the affected train inoperable
Loss of both RN makes both DG’s inoperable making the shared RN valve inoperable
• Use the already inoperable RN to supply the unit with no RN
Donner unit would probably be in 3.0.3
50.54x
If increased and then cooling water restored, pressure can go negative very quickly
Containment pressure
Case II time critical
SNSWP and LLI will be cross tied for the first 10 steps of case II
RN must be aligned to the pond prior to the pond going inoperable
Not expected to occur in any analyzed credible event
If Cowans ford dam fails, lake level will not drop low enough fast enough to get below LLI suction before suction swapped
Air binding RN pumps
What pumps will not have suction if LLI is gone?
RV
