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E-2 — Faulted Steam Generator Isolation

Entered from E-0 when one steam generator shows symptoms of a steam
line break, feedwater line break inside containment, or other rapid
secondary-side depressurization. Identifies the faulted SG, isolates
it to terminate the cooldown source, and preserves at least one intact
SG as the primary heat sink.

Step 1 identify-faulted-sg

Check: which SG has the symptoms — rapidly decreasing pressure («SG-A-PR», «SG-B-PR», «SG-C-PR», «SG-D-PR»), high steam line radiation («SG-A-N16», «SG-B-N16», «SG-C-N16», «SG-D-N16»), abnormal level («SG-A-LVL-NR», «SG-B-LVL-NR», «SG-C-LVL-NR», «SG-D-LVL-NR»), or visible/audible break indications
Caution: identify positively before isolation — isolating an intact SG removes a heat sink
- Faulted SG identified → #verify-intact-sg
- Identification ambiguous → ES-0.0
Because: rediagnosis with expanded symptom check before any SG isolation

Step 2 verify-intact-sg

Check: at least one intact SG available with adequate level and pressure capability
- At least one intact SG → #isolate-faulted-sg
- No intact SG available → FR-H.1
Because: total loss of secondary heat sink — bleed-and-feed required before isolation worsens conditions

Step 3 isolate-faulted-sg

Caution: AFW and MFW to the faulted SG MUST be isolated BEFORE MSIV closure on that SG — closing the MSIV on a still-fed line risks water-hammer on the trapped steam volume and level-swell into the dryer assembly (per WTSM §10.3.2 / Vogtle UFSAR §10.3)
Within: 5 minutes of faulted-SG identification — continued cooldown via the faulted SG must be terminated promptly
Action: in order, (1) isolate AFW to faulted SG via «AFW-A-CV» (or B/C/D as identified), (2) isolate main feedwater via «MFW-A-CV» (or B/C/D), (3) isolate blowdown via «BLOWDOWN-A» (or B/C/D), (4) close the corresponding MSIV — «MSIV-A» / «MSIV-B» / «MSIV-C» / «MSIV-D»
Action: if any isolation valve will not close, manually isolate at the next available downstream boundary
- Isolation complete in sequence → #verify-isolation
Because: ordered isolation prevents water-hammer and SG overfill

Step 4 verify-isolation

Check: faulted SG fully isolated — pressure stabilizing or matching ambient, no continued steam release
- Isolation effective, pressure stable → #align-steam-dump-intact-sg
- Isolation ineffective (continued depressurization) → ECA-2.1
Because: cannot isolate — manage as uncontrolled multi-SG depressurization

Step 5 align-steam-dump-intact-sg

Check: condenser steam dump available AND at least one intact SG in service
Action: align steam dump from intact SG(s) to maintain controlled RCS cooldown after faulted-SG removal from heat-sink chain
Within: 10 minutes of faulted-SG isolation — uncontrolled secondary depressurization of the faulted SG drives unbalanced primary cooldown
Caution: do not steam-dump from the faulted SG even if its MSIV reopens; verify selector is on intact SG(s) only
- Steam dump aligned to intact SG(s), condenser available → #monitor-intact-sg-trends
- Condenser unavailable, steam release via intact-SG PORV → #monitor-intact-sg-trends
Because: PORV release maintains controlled cooldown path when condenser is lost
- No steam release path available on any intact SG → FR-H.1
Because: total loss of secondary heat sink — bleed-and-feed required

Check: intact SG narrow-range level «SG-A-LVL-NR» / «SG-B-LVL-NR» / «SG-C-LVL-NR» / «SG-D-LVL-NR» on non-faulted SGs AND intact-SG pressure trends
Action: maintain intact-SG level at no-load setpoint with AFW; control pressure via steam dump or PORV
Caution: overfeed of intact SG with subsequent return of the faulted-SG flow path can cause primary overcooling — verify isolation persists
- Intact SG levels stable, pressure controlled → #control-rcs-cooldown
- Intact SG level dropping despite AFW alignment → FR-H.5
Because: low intact-SG level threatens the remaining heat sink

Step 7 control-rcs-cooldown

Check: RCS cooldown rate (Tcold trend on «TE-411-COLD», «TE-421-COLD», «TE-431-COLD», «TE-441-COLD»)
Caution: excessive cooldown rate challenges PTS limits and may cause boron dilution from cold-water injection
- Within Tech Spec cooldown rate (typically ≤100°F/hr) → #verify-si-status
- Exceeding cooldown rate → FR-P.1
Because: imminent pressurized thermal shock challenge

Step 8 verify-si-status

Check: SI status and termination criteria
- SI not active (faulted SG isolated, no LOCA symptoms, RCS stable) → #stabilize-on-intact-sg
- SI active AND criteria met → ES-1.1
- SI active AND criteria not met OR LOCA also indicated → E-1
Because: concurrent LOCA + faulted-SG requires LOCA management priority

Step 9 stabilize-on-intact-sg

Action: control intact SG(s) at no-load conditions; restore Tavg via intact-SG steam dump or PORV
- Stabilized → #determine-recovery-path
- Cannot stabilize on intact SG → FR-H.1

Step 10 determine-recovery-path

Check: recovery objective and plant conditions
- Plant stable, no SI, hot standby achieved → ES-0.1
- Cooldown to RHR conditions desired → ES-0.2
- LOCA developed concurrently → E-1

Tags

  • id: SG-A-PR
    description: SG-A steam pressure
    sim-path: secondary.sg.a.steam_pressure
    units: psig
    equipment: sg-a
    source: Vogtle UFSAR §10.3

  • id: SG-B-PR
    description: SG-B steam pressure
    sim-path: secondary.sg.b.steam_pressure
    units: psig
    equipment: sg-b
    source: Vogtle UFSAR §10.3

  • id: SG-C-PR
    description: SG-C steam pressure
    sim-path: secondary.sg.c.steam_pressure
    units: psig
    equipment: sg-c
    source: Vogtle UFSAR §10.3

  • id: SG-D-PR
    description: SG-D steam pressure
    sim-path: secondary.sg.d.steam_pressure
    units: psig
    equipment: sg-d
    source: Vogtle UFSAR §10.3

  • id: SG-A-N16
    description: SG-A main steam line N-16 radiation monitor
    sim-path: rad.msl.a.n16
    units: cps
    equipment: sg-a-msl
    source: Vogtle UFSAR §11.5

  • id: SG-B-N16
    description: SG-B main steam line N-16 radiation monitor
    sim-path: rad.msl.b.n16
    units: cps
    equipment: sg-b-msl
    source: Vogtle UFSAR §11.5

  • id: SG-C-N16
    description: SG-C main steam line N-16 radiation monitor
    sim-path: rad.msl.c.n16
    units: cps
    equipment: sg-c-msl
    source: Vogtle UFSAR §11.5

  • id: SG-D-N16
    description: SG-D main steam line N-16 radiation monitor
    sim-path: rad.msl.d.n16
    units: cps
    equipment: sg-d-msl
    source: Vogtle UFSAR §11.5

  • id: SG-A-LVL-NR
    description: SG-A narrow-range level
    sim-path: secondary.sg.a.level_nr
    units: percent
    equipment: sg-a
    source: Vogtle UFSAR §10.3

  • id: SG-B-LVL-NR
    description: SG-B narrow-range level
    sim-path: secondary.sg.b.level_nr
    units: percent
    equipment: sg-b
    source: Vogtle UFSAR §10.3

  • id: SG-C-LVL-NR
    description: SG-C narrow-range level
    sim-path: secondary.sg.c.level_nr
    units: percent
    equipment: sg-c
    source: Vogtle UFSAR §10.3

  • id: SG-D-LVL-NR
    description: SG-D narrow-range level
    sim-path: secondary.sg.d.level_nr
    units: percent
    equipment: sg-d
    source: Vogtle UFSAR §10.3

  • id: MSIV-A
    description: SG-A main steam isolation valve position
    sim-path: secondary.msiv.a.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: sg-a-msl
    source: Vogtle UFSAR §11.5

  • id: MSIV-B
    description: SG-B main steam isolation valve position
    sim-path: secondary.msiv.b.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: sg-b-msl
    source: Vogtle UFSAR §11.5

  • id: MSIV-C
    description: SG-C main steam isolation valve position
    sim-path: secondary.msiv.c.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: sg-c-msl
    source: Vogtle UFSAR §11.5

  • id: MSIV-D
    description: SG-D main steam isolation valve position
    sim-path: secondary.msiv.d.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: sg-d-msl
    source: Vogtle UFSAR §11.5

  • id: MFW-A-CV
    description: SG-A main feedwater control valve position
    sim-path: secondary.mfw.a.cv_position
    units: percent
    equipment: mfw-system
    source: Vogtle UFSAR §10.4.7

  • id: AFW-A-CV
    description: SG-A AFW control valve position
    sim-path: afw.a.cv_position
    units: percent
    equipment: afw-system
    source: Vogtle UFSAR §10.4.9

  • id: BLOWDOWN-A
    description: SG-A blowdown isolation valve position
    sim-path: secondary.blowdown.a.position
    units: enum[OPEN,CLOSED]
    equipment: sg-a
    source: Vogtle UFSAR §10.3

  • id: TE-411-COLD
    description: RCS loop 1 cold-leg temperature
    sim-path: rcs.loop1.t_cold
    units: degF
    equipment: rcs-loop-1
    source: Vogtle UFSAR §5.1.1

  • id: TE-421-COLD
    description: RCS loop 2 cold-leg temperature
    sim-path: rcs.loop2.t_cold
    units: degF
    equipment: rcs-loop-2
    source: Vogtle UFSAR §5.1.1

  • id: TE-431-COLD
    description: RCS loop 3 cold-leg temperature
    sim-path: rcs.loop3.t_cold
    units: degF
    equipment: rcs-loop-3
    source: Vogtle UFSAR §5.1.1

  • id: TE-441-COLD
    description: RCS loop 4 cold-leg temperature
    sim-path: rcs.loop4.t_cold
    units: degF
    equipment: rcs-loop-4
    source: Vogtle UFSAR §5.1.1