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ECA-3.1 — SGTR with Loss of Reactor Coolant — Subcooled Recovery

Entered from E-3 when SGTR coexists with significant LOCA-style RCS
inventory loss but the RCS remains subcooled (positive «SUB-MARGIN»).
Subcooled cooldown path is preferred because pressurizer remains
controllable and leak termination via depressurization below ruptured-
SG pressure is achievable. Vogtle UFSAR §15.6.3 covers SGTR with
concurrent inventory loss analysis.

CSF: core-cooling

CSF: rcs-inventory

CSF: containment

Step 1 verify-subcooled

Check: RCS subcooling margin «SUB-MARGIN» ≥ 30 °F at lowest cold-leg AND core exit; pressurizer level «PZR-LVL» on-scale and recoverable (rising under charging)
- Subcooled AND inventory recoverable → #initiate-cooldown
Because: subcooled-recovery prerequisites met
- Saturated conditions developing → ECA-3.2
Because: saturated-recovery procedure handles the case where subcooling is lost

Step 2 initiate-cooldown

Within: 60 minutes — leak duration drives integrated release; subcooled cooldown rate is unbounded by saturation but bounded by Tech Spec ≤100 °F/hr
Action: cool down using intact SGs at ≤50 °F/hr (conservative); steam dump via condenser preferred, ARVs «ARV-A» / «ARV-B» / «ARV-C» / «ARV-D» on intact SGs as needed
Action: throttle SI «SI-PUMP-A» / «SI-PUMP-B» to maintain subcooling but reduce mass addition rate that drives pressurizer level
Action: control pressurizer pressure «PT-455» and level «PZR-LVL» during cooldown
- Cooldown on schedule, subcooling maintained → #depressurize
Because: ready to depressurize below ruptured-SG pressure
- Cooldown lagging or subcooling threatened → ECA-3.2
Because: saturated-recovery path engages

Step 3 depressurize

Action: depressurize RCS «PT-455» below ruptured-SG pressure (compare to «SG-A-PR» / «SG-B-PR» / «SG-C-PR» / «SG-D-PR» on the ruptured SG); use pressurizer normal/auxiliary spray or PORV «PORV-456A» / «PORV-456B»
Caution: maintain subcooling margin «SUB-MARGIN» ≥ 30 °F throughout depressurization — too-rapid depressurization can lose subcooling and flip to ECA-3.2
- Leak terminated (RCS pressure ≤ ruptured-SG pressure, no continued primary-to-secondary flow) → ES-3.1
Because: post-SGTR backfill cooldown procedure
- Cannot depressurize (failed PORV, lost pressurizer spray) → ECA-3.3
Because: SGTR-without-pressure-control procedure

Tags

  • id: SUB-MARGIN
    description: RCS subcooling margin (T_sat at PT-455 minus hot-leg temperature)
    sim-path: rcs.subcooling_margin
    units: degF
    equipment: rcs
    source: Vogtle UFSAR §15.6

  • id: PT-455
    description: pressurizer pressure (wide range)
    sim-path: rcs.pressurizer.pressure_wr
    units: psig
    equipment: pressurizer
    source: Vogtle UFSAR §5.4

  • id: PZR-LVL
    description: pressurizer level
    sim-path: rcs.pressurizer.level
    units: percent
    equipment: pressurizer
    source: Vogtle UFSAR §5.4

  • id: PORV-456A
    description: pressurizer PORV 456A position
    sim-path: rcs.pressurizer.porv.456a.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: pressurizer
    source: Vogtle UFSAR §5.4

  • id: PORV-456B
    description: pressurizer PORV 456B position
    sim-path: rcs.pressurizer.porv.456b.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: pressurizer
    source: Vogtle UFSAR §5.4

  • id: SI-PUMP-A
    description: high-head SI pump A status
    sim-path: ess.si_pump.a.status
    units: enum[STOPPED,RUNNING,FAULT]
    equipment: si-system
    source: Vogtle UFSAR §6.3

  • id: SI-PUMP-B
    description: high-head SI pump B status
    sim-path: ess.si_pump.b.status
    units: enum[STOPPED,RUNNING,FAULT]
    equipment: si-system
    source: Vogtle UFSAR §6.3

  • 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: ARV-A
    description: SG-A atmospheric relief valve position
    sim-path: secondary.arv.a.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: sg-a-msl
    source: Vogtle UFSAR §10.3.2

  • id: ARV-B
    description: SG-B atmospheric relief valve position
    sim-path: secondary.arv.b.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: sg-b-msl
    source: Vogtle UFSAR §10.3.2

  • id: ARV-C
    description: SG-C atmospheric relief valve position
    sim-path: secondary.arv.c.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: sg-c-msl
    source: Vogtle UFSAR §10.3.2

  • id: ARV-D
    description: SG-D atmospheric relief valve position
    sim-path: secondary.arv.d.position
    units: enum[OPEN,CLOSED,INTERMEDIATE]
    equipment: sg-d-msl
    source: Vogtle UFSAR §10.3.2