Normal Chilled Water

Question 0

What happens to chilled water supply to the containment ACUs when the fan is not running?

Answer 0

An interlock with the fan circuit closes a motor operated valve stopping chill water flow when the fan isn’t running.

Question 1

What does normal chill water supply?

Answer 1

Containment building, control building, aux building, and rad waste building AHUs and ACUs
Non nuclear, demin, blowdown demin sample coolers
Main generator collector housing coolers

Question 2

How are the chillers operated during times of low heat load?

Answer 2

Only one chiller is operated, but a second circulating pump may be started with its discharge valve throttled to boost system flow without running the second chiller.
This is done to raise the chill water temperature slightly allowing the operating chiller to carry more heat load and operate more stable.

Question 3

How many chillers may be run at max heat load?

Answer 3

2 large chillers and one small chiller.

Question 4

What are the specific loads of concern on a loss of WC?

Answer 4

Containment normal AHUs (tech spec)
Containment refueling purge
Containment power access purge
CEDM control cabinet room
Generator collector housing cooler

Question 5

What supplies cooling water to the chiller packages?

Answer 5

NC and the chiller will trip on low NC flow

Question 6

What is the power supply to the A chiller?

Answer 6

PB

Question 7

Where does makeup water for WC come from and where is it added to the system at?

Answer 7

DW is added to the expansion tank

Question 8

What is added to the system for corrosion control?

Answer 8

N2 is added for corrosion control and for NPSH for the pumps.

Question 9

What is the power supply for the WC circ pumps?

Answer 9

NH

Question 10

What is the power supply for the B, C, and E02 chillers?

Answer 10

NB

Question 11

Where are the WC circ pumps located?

Answer 11

On the aux building roof adjacent to their chillers.

Question 12

What is the N2 pressure maintained on the expansion tank?

Answer 12

15 psig.

Question 13

What is the driving force for chem adds to the WC system?

Answer 13

D/P across the pump

Question 14

How is cooling rate in the compressor controlled?

Answer 14

Automatically by varying the inlet guide vanes positions at suction of the compressor in order to vary refrigerant flow through the compressor

Question 15

How is efficiency improved on the normal chiller units?

Answer 15

An interstage connection between the first and second stages improves efficiency by receiving flash gas from the flash economizer allowing single compression of that portion of refrigerant gas.

The thermal economizer in the condenser portion improves efficiency.

Question 16

When does the oil pump energize in the startup sequence?

Answer 16

28 seconds before the compressor starts.

Question 17

How does the flash economizer increase efficiency?

Answer 17

It has 2 sections, each having a float valve. Sub cooled liquid passes through the high side float valve into the economizer then through a low side float valve. Pressure reduction and expansion takes place reducing the fluid temp. Some of the fluid flashes to vapor due to entering a low pressure region removing more heat. The vapor goes back to the 2nd stage compressor.

Question 18

What is surging?

Answer 18

It occurs during low load operations.
Pressure in the condenser momentarily becomes higher than the pressure at the compressor discharge allowing back flow into the compressor.
It’s minimized by the use of a hot gas bypass. The hot gas bypass increases the refrigerant temp. In the cooler causing chill water temp to increase causing inlet vanes to open some and maintain adequate discharge pressure.

Question 19

What is stacking?

Answer 19

Low load conditions that result in excessive condenser cooling cause it.
Flow rate through the compressor to the condenser is low. The D/p between the condenser and cooler decreases and refrigerant starts stacking up in the condenser while refrigerant level in the cooler decreases.
Stacking is not normally a problem with these chillers.

Question 20

How long do you have to wait to restart a chiller after a trip?

Answer 20

15 minutes (white light is on during timer)

Question 21

How long do you have to wait to start a chiller that was manually shut down?

Answer 21

20 minutes

Question 22

What must chill water temperature be to reset the start circuitry after an auto load recycle?

Answer 22

45F

Question 23

What will auto close the containment normal chill water isolation valves?

Answer 23

CIAS

Question 24

What is the power supply to A chiller circ pump?

Answer 24

NHN- M19 SIAS load shed panel. AO must reset it after Load shed and PB is re energized

Question 25

What will happen if WC supply temperature reaches 50F?

Answer 25

Alarm in the control room.