Decay Heat System Flashcards
What is the purpose of piggyback mode and how is it accomplished?
Piggy back mode of operation is used when RCS pressure too high for LPI injection, but BWST inventory has been depleted. DH system is used to provide suction to the HPI pumps using RB sump as source of inventory through CV-1276/1277.
What will cause CV-1050/1410 auto close and what pressure instrument is it fed from? When does this interlock reset?
CV-1050/1410 will auto close if CFT outlet MOVs come off of their closed seat or ESAS analog channel 1/2 wide range pressure instruments reach 320 or 385 psig.
The interlock is reset at 290 psig.
What is the interlock associated with the RCS/BWST suction valves and what is its purpose?
Interlock prevents the RCS suction valves from being opened when aligned from the BWST to prevent overpressurizing the ECCS piping.
What is the max allowable LPI flow rate and what is the LPI hi/lo flow alarms?
The max allowable LPI flow is 4000 gpm.
LPI Hi flow alarm is 3750 gpm. If flow is high ACA directs manual override of associated block valve and throttling flow < 3750 gpm.
LPI Lo flow alarm is < 2800 gpm or bkr tripped open, 35 seconds after ES 3 or 4 actuation.
What is the hi/lo flow limits/alarms associated with Decay heat operation?
> 375’ -> Hi flow alarm is > 3550 gpm
< 375’ -> Hi flow alarm is > 2000 gpm
Lo flow alarm -> both DH loops < 1000 gpm
What is the minimum recirc flow for DH pumps?
80 gpm
What RCS temperature/pressure is DH allowed to be placed in service?
DH procedurally is directed to be placed in service when RCS < 250 psig, < 280 degrees F.
What D/P will the DH pumps output?
150 psid
What position is SW-22A/B in, why is it in this position and how is it operated? When can SW-22 be operated outside of its Scribe T position?
SW-22A/B is throttled to scribe T position (CAT-E). This position ensures adequate flow through the DH cooler (> 1600 gpm). While maintaining enough pressure to other SW components (primarily RB Coolers and EDGs).
SW-22 is throttled one turn past scribe T and then back to the scribe T position and locked.
SW-22s can be operated for additional cooling in mode 5 when temperature is less than 200 degrees F when SW is no longer required per TS.
What ES channels actuate DH and what time delay is associated with it for EDG loading?
ES channels 3 and 4 actuate LPI. A 10 second time delay is associated with pump starts for EDG loading, independent of EDG operation.
Describe operation of the DH Room coolers and what actions are taken when maintenance is performed?
The lead room coolers (VUC-1 A/C) will autostart on a LPI or RB spray pump start. If does not develop adequate flow the lag cooler (VUC-1B/D) will start after 15 seconds of degraded flow.
When maintenance is being performed on the lead coolers, the associated lag cooler is placed in service since it would not get a start signal with the lead cooler de-energized.
What components are started based on pump start vs ES actuation?
Pump Start - SW bearing cooler and SW inlet valves open, Room cooler starts, process monitor starts
ES - pump starts, DH cooler outlet and block valve receive open signals, DH cooler bypass valve closes and associated BWST outlet valve opens
What’s the purpose of the flow cavitating venturis?
Flow cavitating venturis provide backpressure during a discharge line break to minimize flow out the break when flow exceeds 2000 gpm.
Where does DH suction and discharge tie into the RCS?
DH suction line taps off of A Thot line and discharges into Reactor Vessel through associated lines.
What is the purpose of LP Aux Spray, when is it used and how is it accomplished?
LP Aux spray is used to provide RCS pressure control when RCPs are secured. Prior to going on RB sump recirc LP aux spray will be aligned by opening DH-4A or B and DH-94 to minimize dose received.
What is the purpose of the BWST, associated TS and how many gal/ft?
Purpose: Backup source of borated water for reaching Cold S/D, Source of borated water for emergency conditions, Filling Fuel-Transfer Canal
Tech Specs
40.2 +/- 1.8 ft
2470 +/- 200 ppm
40 - 110 degrees F
BWST is 9,639 gal/ft
What is Vortexing during DH operation and how is it detected?
Vortexing occurs due to low RCS levels and lack of suction to DH pumps. Vortexing can be detected by fluctuating flow, pressures and an annunciator set by CR operators based on amperage.
What is the DH pump discharge relief valve value?
445 psig
ECCS system is designed to protect against what four accidents?
1) LOCA
2) Rod Ejection
3) SG Tube Rupture
4) Main steam line break
How long can DH be in recirc mode without service water aligned to DH Cooler?
20 minutes to prevent overheating pump casing
What methods of makeup are available if loss of DH experienced?
When RCS temperature less than 259 degrees F, what actions are required for LTOP?
- HPI Block valves closed and in LTOP position (prevents opening)
- ERV setpoint at 400#
- ERV isolation closed
- PZR level limits
What is the max suction pressure allowed when aligned to RCS? Max temperature?
300 psig
280 degrees F
What is the maximum delta T limit when securing RCPs and why?
Max delta T between DH cooler outlet and RCS temperature is 25 degrees F due to potential damage to LPI/DH nozzles from thermal stresses
What is the maximum time a DH pump can be deadheaded?
30 seconds
Why is DH flow limited < 2000 gpm when RCS is depressurized?
Unless required for cooling, DH flow is limited < 2000 gpm to limit venturi cavitation and flow induced vibration
How are the DH pumps initially started based on RCS pressure?
> 150 psig: DH pump is started with DH cooler outlet closed, CV-1400/1401 open and DH cooler bypass valve 74 - 80% open.
< 150 psig: DH pump is started with DH bypass and DH cooler outlet closed to minimize water column separation in suction piping.
