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 methods of makeup are available if loss of DH experienced?
