SBGT

Question 1

What is the purpose of the Standby Gas Treatment System?

Answer 1

Maintain small negative pressure of 0.25”WC in RB under secondary containment isolation condition to minimize ground level release of airborne radioactivity.

Question 2

What is the flow through SBGT (total)?

Answer 2

4000scfm primary train;
300scfm cooling flow;
Total 4300normal;
4000cfm +10% is tech spec limit

Question 3

How is the SBGT sized for flow and air purification?

Answer 3

Sized to provide 1 air change per day in RB

Question 4

Where does SBGT discharge to?

Answer 4

310’ chimney

Question 5

Where does SBGT take suction from?

Answer 5

RB Vent (between Rad Element & RB Vent exhaust dampers)
U2/3 DW and Torus (only if <62psig)
U2&3 HPCI gland exhauster
U2&3 DW & Torus via APCV

Question 6

What elements are included in the SBGT Air Filter Unit and what is their purpose?

Answer 6

Demister - removes bulk moisture to lower humidity
Heater - to raise temp and humidity to improve efficiency
Rough Filter - to remove large particulates
HEPA Filter - remove 99% particulates >=3micron
Charcoal filter - removes 95% of iodine at flow of 4000scfm
After filter - removes free charcoal that has come dislodged.

Question 7

When does the SBGT Heater start?

Answer 7

When adequate flow is achieved.

Question 8

What supplies actuation force for SBGT Flow Control Dampers?

Answer 8

A Train from U2 IA

B Train from U3 IA

Question 9

What supplies air signal to the A Flow transmitter? B? What happens if both fail?

Answer 9

Both are supplied by U2 IA.

A fail safe accumulator is provided to ensure they fail open on loss of IA or loss of control power

Question 10

What provides power to A Train SBGT electrical components? Control power? B Train?

Answer 10

A Train from MCC 29-9; Control power from U2 ESS

B Train from MCC 39-2; Control power from U3 ESS

Question 11

What are the positions for the SBGT Inlet Dampers?

Answer 11

Normally closed, auto open on initiation signal

Question 12

What are the SBGT Outside Air Supply Dampers?

Answer 12

They are normally open and provide for removal of decay heat on SBGT train which is not running.; On system initation, damper for running train closes.

Question 13

What provides motive force for ambient decay heat removal in SBGT?

Answer 13

Dampers on standby train is open, running train fan creates suction flow of 300scfm through filter unit and through crosstie to running train

Question 14

Where does removed moisture from SBGT demister route and how is the secondary containment boundary maintained?

Answer 14

Removed moisture to Radwaste. Filled loop seals maintain secondary containment.

Question 15

What is the purpose of the SBGT Electric Heater?

Answer 15

Raises air temp by 14deg to lower humidity to 70%.

Auto start when flow >2600scfm

Question 16

What is the effect of excessive flow in SBGT?

Answer 16

Flow over 4000 scfm through AFU lowers efficiency of charcoal adsorber beds.

Question 17

How does the SBGT crosstie damper function?

Answer 17

Normally locked open and allows cooling of train in standby.

R.O. limits flow to 300sfcm through standby train.

Question 18

What poweres and positions Flow control dampers?

Answer 18

A -U2 IA, U2 ESS

B - U3 IA, U3 ESS

Question 19

What are the SBGT Auto Start Signals?

Answer 19

Grp 2 Isolation - Air
Lo Rx Level,
Hi DW Rad
Hi DW Press; OR
Rx Vent Exhaust Hi Rad (4mR/hr - 1 out of 2 Hi or both downscale)
Refuel floor hi rad (45mR/hr - 1 out of 2 HI or both downscale)

Question 20

What can impact capabilities of SBGT filtration and how?

Answer 20

VOC’s from painting <24hr prior or 3 hrs of propane operated equipment in power block - RB or TB 534.
- limited to 400ft^2 of epoxy paint -
These VOCs can damage charcoal adsorbers

Question 21

What occurs on SBGT Autostart?

Answer 21

on “PRIMARY TRAIN”: Inlet MO damper open, cooling damper close, fan starts, fan discharge MO opens, flow control damper throttles
IF AFTER 20 Sec - low flow conditions or heater is off on primary train, then it trips and standby train starts. stdby keeps running even if low flow
STANDBY only AUTOSTART if PRIMARY was NOT manually started.

Question 22

What are SBGT Alarms?

Answer 22

Loss of Heater Power
Low flow in Op Train
HI Temp
Control Switch in OFF

Question 23

What happens in loss of IA

Answer 23

SBGT Flow Control Dampers FAIL OPEN - may cause excessive flow
U2 supplies both flow control transmitters - loss of U2 IA causes BOTH flow control dampers to fail open. Only U3 FCDamper fails open if loss of U3 IA

Question 24

What can cause Lo Flow in SBGT?

Answer 24

Failure of FC Damper or controller
Plugging of filter or adsorber
Loss of Fan

Question 25

What happens on loss of U2 ESS?

Answer 25

Auto Start logic to affected train disabled

If A running, it will shutdown and B train will autostart (ONLY IF AUTO SIGNAL PRESENT)

Question 26

What is IB interface with SBGT?

Answer 26

Provides initiation logic for rad monitors - the relay de-energizes on loss of power and starts SBGT

Question 27

What powers the Trains SBGT Flow transmitters?

Answer 27

U2 2B-1 through ATS
U3 - MCC 39-1 through ATS

LOSS OF THIS WILL: fail instruments to low flow condition - and will never clear low flow signal

Question 28

How many SBGT trains are required to be operable and in what modes?

Answer 28

In MDs 1,2,&3; 2 are required to be operable. If 1 is INOP, you have 7 days to restore, if 2 INOP, you have 1 hr to restore one of them.

IF moving recently irradiated fuel:
1 INOP - place other in service IMM
OR Stop fuel moves IMM
2 INOP - STOP FUEL MOVES IMM