ATWS/ARI-RPT

Question 1

What is the Purpose of ATWS/ARI-RPT?

Answer 1

Prevent core uncover and melting and possible fission product release if a reactor scram fails to shutdown nuclear reaction after anticipated transient

Question 2

What design features does ATWS/ARI-RPT have?

Answer 2

Diverse from RPS
Any component capable of single failure rod insertion is highly reliable
Testable w/ Rx in Service
High Quality EQ Components

Question 3

What methods does ATWS/ARI-RPT have to fulfill it’s design function?

Answer 3

Reduced core flow via RR Pp trip - ATWS immediately trips ASD input breakers on high pressure and after short time delay on lo-lo level
Six ARI Vlvs on Scram air header- designed to vent scram air header when ENERGIZED

Question 4

What type of electrical signal is required to ACTUATE ATWS/ARI-RPT?

Answer 4

It is ENERGIZE to actuate

Question 5

ATWS/ARI-RPT has two divisions. How many trip channels from each subsystem are required to actuate?

Answer 5

The two divisions are designed redundantly. Both channels from a single division are required to actuate the ATWS/ARI-RPT trip

Question 6

What is the power source for the ATWS/ARI-RPT LOGIC?

Answer 6

The 125vdc control power from the associated RR ASD Input Breaker

Question 7

Upon an AUTOMATIC ATWS/ARI-RPT initiation, what will actuate?

Answer 7

The Trip coil for the same division RR ASD Input Breaker.
The Emergency Stop for the OPPOSITE RR Pp
Three ARI vlvs from that division

Question 8

How is the ATWS Manual Initiation performed and what actuates?

Answer 8

Arm atleast 2 pushbuttons from same division, and press them both
3 ARI valves will open to dump the scram header
THE RR PUMP WILL NOT TRIP FROM THESE PUSH BUTTONS

Question 9

WHAT is the electrical actuation method for ATWS Logic?

Answer 9

Energize to Actuate

Question 10

What is the power supply for Div I ATWS instruments? Div II?

Answer 10

Div I: IB & 125 vdc 2A-1
Div II: ESS & 125vdc 2B-1
Loss of single power source in a division will not result in a loss of that divisional function

Question 11

What happens to ATWS with a loss of control power to Bus 21?

Answer 11

You will lose 125vdc to ATWS/ARI-RPT Logic, When 2A-2 is swapped, then ATWS power is also swapped

Question 12

How does ATWS impact the Turbine, HPCI and RFP?

Answer 12

It provides a trip to all of them on a Hi Level of +48” from 23A/B/C/D
Protects turbine from moisture carryover and trips RFP to stop increase of water inventory. RFP and Turbine must be restarted when Hi Level clears

Loss of HPCI Rx Hi Level Trip Unit is a 24 hr LCO 3.3.5.1 to restore (No INOP)

Question 13

What causes ATWS/ARI-RPT to actuate?

Answer 13

Need 2 lo lo level signal OR 2 hi Pressure signal OR 1 of each (not standard)

Question 14

What are the setpoints for ATWS/ARI-RPT?

Answer 14

Hi Rx Pressure - 1200#

Lo-Lo Level - -59” - Immediately opens ARI vlvs - waits 9 seconds before tripping RR Pps

Question 15

How long does ARI initiating signal seal in for? why?

Answer 15

49 seconds - to provide enough time for the scram air header to bleed off

Question 16

What is the time delay for the Rx Lo-Lo level?

Answer 16

9 seconds before tripping RR Pp - ARI vlvs open immediately

Question 17

What happens to ATWS/ARI-RPT on loss of 125vdc 2A-1 or IB?

Answer 17

the other ATWS supply will pick up load and ATWS will continue to function.
The PS-1A light out indicates loss of 2A-1
PS-2A indicates loss of IB
PS-3A light out indicates loss of inverter
125VDC Sys ON light out indicates loss of logiv power from 2A-2

Question 18

What happens on a complete loss of power to ATWS Division?

Answer 18

Enter Tech Specs because of loss of divisional instruments and trip functions.
The other division will be able to perform the trips and open ARI valves

Same as if power to ATWS logic lost

Question 19

How can ARI be defeated?

Answer 19

Pull Fuses - ATWS RR ASD E-Stop trip still operable

Question 20

Where are the ATWS/ARI-RPT time delays powered from?

Answer 20

9 second RR Pp Trip delay from ATWS Auctioneered power

49 secon reset time dealy from 2A-2/2B-2 from breaker control power

Question 21

What happens with a loss of one or more channel of lo-lo level or hi steam pressure?

Answer 21

14 day time clock per 3.3.4.1

Question 22

What do the NEON lights