AB.SW-0001 Attachment 4 — leak isolation based on location relative to 21SW22 (NUCLEAR HEADER):
• Leak DOWNSTREAM of 21SW22 (Step 2.0): CLOSE 21SW22 and ENSURE CLOSE 21SW23 and 22SW23 (TIE VALVES). After isolation, SW cooling is NOT available to 21CFCU and 22CFCU.
• Leak UPSTREAM of 21SW22 (Step 3.0): CLOSE 21SW22 and ENSURE OPEN 21SW23 and 22SW23 (TIE VALVES) — maintains cross-header supply to the isolated header's loads.
Trap: tie valve position (open vs closed) depends entirely on whether the leak is upstream or downstream of 21SW22.

OHA B-48 (SW VLV RM FLOODED) indicates leak in SW valve room on 78' Mechanical Penetration Area. CFCU piping in this room before containment penetration.

AB.SW-0001 may be the first procedure entered due to OHAs B-13 and B-14 (low SW header pressures). However, with OHA B-29 (21-23 SW PMP SMP AREA LVL HI) also alarming, AB.SW-0001 immediately transitions the crew to AB.SW-0003 (Service Water Bay Leak) for bay isolation. AB.SW-0001 provides attachments for isolating various leaks but does NOT contain the steps for isolating a SW Bay.

AB.SW-0001 Attachment 5 — isolating a SW leak on a CFCU: close SW72 (Outlet Water Valve) FIRST, then close SW58 (Inlet Water Valve). The basis for closing the outlet valve first is to minimize the possibility of water hammer following restoration. Trap: closing the inlet valve first (SW58) seems intuitive to stop flow, but it creates conditions for water hammer when the system is restored. The field manual isolation valves (SW54 inlet and SW76 outlet on 78' elevation) are closed after the MOVs.