Containment - Air Control

Question 1

What systems support Containment Air Control?

Answer 1

Nitrogen Makeup, Pumpback System, DW Cooling, DW purge, Augment Primary Cotnainment Vent (APCV

Question 2

What is the prupose of the Nitrogen Makeup System

Answer 2

Provides pressure control support to primary containment.
Also performs feed and bleed to prevent combustible atmosphere;
May be used as system to inert the DW - vaporizing liquid N2 at flow rate of 2500cfm.

Question 3

What is the purpose fo the Nitrogen containment atmospheric Dilution (NCAD?

Answer 3

Provides more reliable combustible gas control

Used as backup makeup flow path during accident conditions

Question 4

What is the Pumpback System?

Answer 4

Used to maintain DP at slightly greater than 1psid between DW and torus via supply air operated vavles in DW.

Question 5

Where are the Pumpback Air Compressors?

Answer 5

North of West (East) HCU Bank on U2 (U3)

Question 6

What is the power source for the Pumpback air compressors?

Answer 6

MCC 28-1 (38-1) and 29-1 (39-1)

Question 7

What provides the cooling for the Pumpback Air Compressors?

Answer 7

U2 RBCCW cools all of them for both units.

Question 8

What are the trip setpoints for the Pumpback Air Compressors?

Answer 8

Low oil pressure (15-17psig)
High RBCCW temp 180F
Low Suctio Pressure 5"Hg
Breaker Trip
***If one compressor trips, the other must be started manually

Question 9

What happens to the pumpback air compressor on a group II isolation?

Answer 9

It will run unloaded due to Air isolation and will likely trip on low suction pressure.

Question 10

What is normal flow for pumpback air compressor?

Answer 10

Suction from Torus and discharge to DW

Question 11

How does the DW/Torus DP control System Function?

Answer 11

Pumpback Compressors suction off Torus and charge receiver to 100psig, then supplies flow back to DW via PCV
PCV used to control flow and set to maintain DW Pressure slightly higher than 1psig.
Receiver also supplies a line to the DW pneumatic system dryer and to DW Pneumatic receiver to support AO isolation valves and DW valves

Question 12

What happens with degraded pressure on Pumpback and Drywell Pneumatics?

Answer 12

N2 backup valve opens to maintain pressure to valves in DW.

This is requried to maintain MSIV’s

Question 13

What may cause changes to DW pressure during normal Operation?

Answer 13

Convective heating during startup or power reduction
Pumpback malfunction
DW pneumatic leak
Change in ambient pressure (relative to RB pressure

Question 14

What is the purpose of DW Pneumatics?

Answer 14

Supplies pressure to DW AOVs

Question 15

How do the Containment Dampers respond on loss of pumpback?

Answer 15

Fail safe accumulators provide pressure to operate valve through a couple of cycles if pumpback lost.

Question 16

What is normal setpoint for DW temperature?

Answer 16

135 to 150F - maintained by DW coolers

Question 17

What provides cooling to DW cooler fans?

Answer 17

RBCCW

Question 18

What powers the DW Cooler Fans?

Answer 18

Bus 28 for A, B, F, G; Bus 29 C, D, E

Question 19

How do the DW Coolers respond to ECCS initiation?

Answer 19

Trip and breakers trip.

Do not trip on load shed.

Question 20

What is the purpose of the DW purge fans? Power?

Answer 20

Draw primary containment atmosphere through set of filters and dischage to RB vent exhaust fans and out RB Stack or SBGT.
Powered by MCC 28-1 and 29-1

Question 21

How does DW Purge Fan Respond eto Secondary Containment Isolation?

Answer 21

Both Units purge fans trip and inlet and outlet dampers close

Question 22

What is the Augmented Primary Containment Vent System (APCV)?

Answer 22

Provides capability to vent Primary Containment following accident should all primary containment cooling be lost and containment pressure approach design limit by providing rapid vent means.

Question 23

What is the design flow for APCV?

Answer 23

Equivalent to 1% rated thermal power at 62psig torus bottom pressure and maximum normal Torus water level

Question 24

What provides power to APCV?

Answer 24

ESS supplies power to logic and valve solenoids (valves fail closed).

Question 25

What happens to Nitrogen Makeup on Group 2 isolation?

Answer 25

Signal to close dampers (57 through 59)

Question 26

How may the Drywell Cooling ECCS trip signals by bypassed?

Answer 26

Lifting and taping leads per DEOP 500-02

Question 27

If there is a loss of Instrument Bus or Air how will Pumpback Respond?

Answer 27

DW to Torus DP PCV fail closed;
DW Pneumatic to DW Isolation valve fail closed;
DW Pneumatic N2 Backup Valve Fails Closed;
Loss of Instrument Bus will cause AOVs supplying DW pneumatics to fail closed and Inboard MSIVs fail closed on loss of N2.

Question 28

Loss of Pumpback will…..

Answer 28

Cause DW to Torus DP to drift and exceed design/TS limits