NSSSS - 1.0

Question 1

What is the purpose of NSSSS?

Answer 1

The NSSSS develops and initiates isolation signals for the reactor vessel and primary containment isolation valves for systems directly connected to the RPV.

Question 2

Describe the actuation motive force.

Answer 2

De-energize to actuate

Question 3

Of the NSSSS channels, what channels are required to trip what components?

Answer 3

1) Inboard Isolation Valves - Channels A and B
2) Outboard Isolation Valves - Channels C and D
3) Main Steam Isolation Valves - Channels A or C and B or D

Question 4

What does depressing the B or C NSSSS pushbuttons do?

Answer 4

Nothing

Question 5

What does depressing the B and C NSSSS pushbuttons do?

Answer 5

Close MSIVs

Question 6

What does depressing the A and D NSSSS pushbuttons do?

Answer 6

Close all NSSSS valves

Question 7

What channels of NSSSS must actuate to close the MSIVs and Drains?

Answer 7

channels A or C AND B or D

Question 8

What are the automatic isolation conditions for the MSIV trips?

Answer 8

• RPV Level 1 (-129”)
• Low Condenser Vacuum (21.5” HgA)
• Low MS Line Pressure (Mode Switch in Run and < 756 psig)
• MS Line High Flow (162.8 psid)
• MS Tunnel High Temp (160F)

Question 9

If a NSSSS trip occurs with the MSIVs and they are shut, what conditions must be met before the valves can be reopened?

Answer 9

Reopening the MSIVs after closure IAW plant procedures, requires MSIV switches be placed in “close”

Question 10

What are the automatic isolation conditions for the Reactor Recirc Sample Lines (SV-4310(4311) trips?

Answer 10

A & B (C & D) or A (D) manual
* RPV Level 2 (-38”)
* Main Steam Line HI Rad (3.0 x Normal Full Power Background)

Question 11

What are the automatic isolation conditions for the RWCU Pump Suction Valves trips?

Answer 11

F001 (A & B or A Manual) and F004 (C & D or D Manual)
* RPV Level 2 (-38”)
* Diff Flow Hi (56.3 gpm, 45 sec TD)
* Area Temp Hi
1. 4402 Pipe Chase (160F) – EOP-103 Entry
Condition
2. Pump OR HX Rooms (140F)
3. 4505 Pipe Chase (135F)
* Ventilation Differential Temp (60F)
* SLC Initiation (A Pump – F001 Closes, B Pump –
F004 Closes)
* NRHX outlet 140F (F004 only)

Question 12

What are the automatic isolation conditions for the RHR S/D Cooling Valves trips?

Answer 12

• RPV Level 3 (+12.5”)
• RPV Press High (82 psig)
  Note: SDC valves require an input from A/B (Inboard) or C/D (Outboard) so only an ‘A’ or ‘D’ manual isolation will have any effect. However, since the high pressure trips are only single coincidence, a loss of either RPS bus, will result in all SDC isolation valves closing.

Question 13

What are the automatic isolation conditions for the RHR Sample and Radwaste (F049/F079(40/80) trips?

Answer 13

A & B (C & D), A (D) Manual)
* RPV Level 3 (+12.5”)
* Hi Drywell Pressure (1.68psig)
Note: These differ from SDC valves only in that the Hi DW Press has coincidence, therefore only a loss of A(D) channels will cause the valves to close.

Question 14

What are the automatic isolation conditions for the TIP isolations trips?

Answer 14

• RPV Level 2 (-38”)
• Drywell High Pressure (1.68psig)
• Gas Purge Only Isolates on RBV Exhaust 1x10-3uci/cc (Via PCIS, not NSSSS)

Question 15

What isolates in NSSSS based on 1.68# in the drywell?

Answer 15

Nothing

Question 16

What happens to SDC valves on a low RWL?

Answer 16

A/B shut F009 while C/D shut the F008 and F0015. Pressure transmitter only requires one 1 to cause iso. A loss either RPS bus closes all SDC valves.

Question 17

How are the MSIV isolation signals reset?

Answer 17

Both RPS busses must be energized and MSIV switches taken to close before resetting logic.

Question 18

What happens if control is transferred to RSP?

Answer 18

If transferred, NS4 logic will not isolate valves. The 82# permissive to go into SDC remains active.