SBGT (T46) Flashcards
How are SBGT filter trains arraigned?
(Does He Feel He Can Help)
DEMISTER (moisture separator)
Designed to remove 99.9% of moisture particles ≥ 2 microns and 30% of those > 1 micron
Electric Heater
Lowers relative humidity to < 70%
Improves charcoal efficiency by preventing moisture from coating the surface of the charcoal
Prefilter
Removes large particles and protects the high efficiency filter
High Efficiency (HEPA) Filter Removes radioactive particulates of 0.3 microns or larger
Activated Charcoal Bed
Removes iodine in the form of methyl iodide and elemental iodine
Work thru the process of adsorption (Adherence of a gas molecule to surface of a solid)
99.9% efficient for the removal of iodine and 95% efficient for methyl iodine
2nd HEPA filter
Catches charcoal fines, which might leave the charcoal bed
Blower (Fan)
Provides motive force for system to maintain >0.20” H2O dp b/w Secondary Containment & outside bldg atmosphere
U2 fans are located internal to the filter train
U1 fans are located in the respective discharge piping
Where does U1/U2 SBGT take suction?
How do suction valves fail?
U2 SBGT takes suction from Rx Bldg & RF floor areas airspace
U1 SBGT takes suction from Rx Bldg & RF floor ventilation ductwork
Both also have DW/Torus Purge suction
U2: F001 Rx Bldg, F003 Refuel Floor to each filter train (4 valves total)
U1: F001 suction valves for all sources to each filter train (2 valves total)
U2: F001/F003 valves fail open on loss of air (NIEIA)
U1: F001A/B valves fail closed on loss of power to solenoids
What are the SBGT Initiation Signals?
What trains start, how long do they run?
Low RWL -35”
Hi Drywell Pressure 1.85 #
Rx Bldg Vent Hi Rad (K609) 18 mRhr
R/F Vent Hi Rad (K611) 18 mR/hr
U2 R/F Vent Hi Rad (K634) 6.9 mR hr
(K635) 5.7 mR/hr
U1 ONLY - Loss of RPS A or B
Radiation Monitor auto start
Rad monitors are grouped: “A” and a “B” high rad monitor reaching a high set point starts the “A” SBGT
“C” and “D” monitors actuate to start the “B” SBGT
Train that starts tells rest of trains to start
ALL 4 TRAINS START on any initiation signal with suction from both RB and RF for both units.
U1/U2 RF & Rx Building Ventilation Trips & Isolates
U1 SBGT fan will trip after TD:
A-6min
B-4 min (weaker fan)
This will leave 3 fans running after 4 minutes.
What is the unit difference for SBGT filter train discharge?
Where does SBGT discharge?
U2 trains stay SEPARATE with 2 isolation valves (F002 A/B)
U1 trains have a COMMON DISCHARGE isolation valve (F005)
The filter trains discharge to the main stack to provide for an elevated release point. (100 meter)
What are the SBGT system trips?
Where are they reset?
Overload
Charcoal Bed Temp Hi ≥ 200°F (U1 only)
Heater Outlet Temp Hi CR1 ≥290°F; CR2 ≥ 190°F (U2 only)
Low Flow after auto start (U1 only) A – 6 min, B – 4 min
U2 system trips may be reset locally or in MCR at P654/P657
All U1 system trips must be reset locally
What are the SBGT fan power supplies?
What is SBGT control power?
U1/U2 A Fan: 600 “C” (R24-S011)
U1/U2 B Fan: 600 “D” (R24-S012)
CRITICAL INST A & B (R25-S066/S067)
U2 isolations – Fail open on loss or loss of air (NIEIA)
U1 isolations – Fail closed on loss or loss of power to solenoids
What is the purpose of the Excess Flow Isolation Dampers? At what flowrate will the Drywell/Torus Excess Flow Isolation Dampers close?
Drywell/Torus Excess Flow Isolation Dampers 2T46-F076/F077 (1T48-F392/F393)
Designed to prevent excessive flow and pressures during a LOCA from DAMAGING THE FILTER TRAINS
Auto close at a flow rate of 3900 to 4800 scfm
Close on high flow to prevent flow from becoming excessive
Designed to limit downstream pressure to 2 psig in the event of a LOCA
A 2” bypass line around dampers prevents stopping all flow in the event a train is operating and the dampers shut due to high flow
What effect does Loss of RPS have on U2/U1 SBGT?
U2 no effect (Logic from INST A)
U1 Loss of RPS A or B, Both Trains of SBGT start (RPS Logic)
What are the 4 positions for the SBGT control switch, and what does each position do?
OFF - secures the respective filter train and removes all auto-initiations.
AUTO - normal position when the SBGT system is in Standby.
RUN - is used to manually start the system.
STBY - will secure the respective filter train but will allow it to restart if low flow is sensed in the running filter train
A switch placed in standby (STBY), the fan will auto start if the other fan for the same unit is not operating
What is the purpose of the Deluge Reset PB 6A/B?
Used to reset heaters and fans after a charcoal bed high temperature trip.
What is the function of the Fan/Heater Auto Start Reset SR 1/2 (Unit 2 only)?
Fan/Htr Auto Start Reset SR1/2 (Unit 2 only):
- Used when securing the SBGT system after an automatic initiation.
- Resets the auto-start logic
