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FR-H.4 — Response to Loss of Normal Steam Release Capabilities

CSF heat sink — YELLOW path. Entered when the condenser steam dump
is unavailable — either condenser vacuum is lost, turbine-bypass valves
have failed, or the main condenser is isolated. Without condenser steam
dump, SG pressure must be controlled via atmospheric relief valves
(ARVs), which discharge directly to atmosphere. Continued operation in
this regime depletes condensate inventory faster, releases noble gases
to the environment, and is the precursor to FR-H.2 (overpressure) if
atmospheric relief also fails.

CSF: heat-sink

Step 1 verify-loss

Check: condenser steam dump «STEAM-DUMP» availability indicators (turbine-bypass-valve auto-disabled, condenser vacuum «CONDENSER-VAC» degraded below operating range, condenser isolated); SG pressures «SG-A-PR» / «SG-B-PR» / «SG-C-PR» / «SG-D-PR» trending up
Caution: a temporary turbine-bypass mismatch with TAVG controller is not loss of steam dump; criterion is sustained unavailability
- Condenser steam dump confirmed unavailable AND SG pressures rising → #use-atmospheric
Because: ARV alignment is required to prevent escalation to overpressure
- Condenser available, transient on TAVG controller → E-0
Because: false alarm; return to diagnostic flow

Step 2 use-atmospheric

Within: 5 minutes — SG pressure rises ~5 psi/min without relief at decay-heat power
Action: align atmospheric relief valves «ARV-A» / «ARV-B» / «ARV-C» / «ARV-D» for steam release; set pressure control to maintain post-trip no-load setpoint (~1010 psig)
Action: verify TDAFW pump «AFW-PUMP-T» continues running on SG steam (TDAFW steam supply unaffected by condenser status; AFW continues feeding)
Caution: ARV release is direct-to-atmosphere — coordinate with rad-engineering and emergency-response organization (ERO); if any SG has a tube leak, ARV release is the radiological release path
Note: Vogtle ARVs are nitrogen-powered with backup air; verify nitrogen supply «N2-SUPPLY» during extended operation
- ARVs aligned, SG pressures controlled at target → #monitor
Because: alternative steam-release path established
- ARVs unresponsive or cannot maintain pressure control → FR-H.2
Because: overpressure response handles the case where no relief path works

Step 3 monitor

Check: SG pressures «SG-A-PR» / «SG-B-PR» / «SG-C-PR» / «SG-D-PR» stable at target; RCS cooldown rate not exceeding Tech Spec (≤100 °F/hr); condenser-recovery status
Within: re-evaluate every 15 minutes during continued atmospheric relief operation
- SG pressures stable AND cooldown rate within Tech Spec → E-0
Because: stable operation on alternate steam-release path; return to diagnostic flow
- SG pressures rising despite ARV operation → FR-H.2
Because: relief inadequate; overpressure response engages

Tags

  • id: STEAM-DUMP
    description: condenser steam dump availability (auto-permissive flag)
    sim-path: secondary.steam_dump.available
    units: bool
    equipment: secondary
    source: Vogtle UFSAR §10.4.4

  • id: CONDENSER-VAC
    description: condenser vacuum (absolute pressure)
    sim-path: secondary.condenser.vacuum
    units: inhga
    equipment: secondary
    source: Vogtle UFSAR §10.4.1

  • 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

  • id: AFW-PUMP-T
    description: turbine-driven AFW pump status
    sim-path: afw.pump.tdafw.status
    units: enum[STOPPED,RUNNING,FAULT]
    equipment: afw-system
    source: Vogtle UFSAR §10.4.9

  • id: N2-SUPPLY
    description: ARV nitrogen-supply pressure
    sim-path: secondary.arv.n2_supply.pressure
    units: psig
    equipment: arv-system
    source: Vogtle UFSAR §10.3.2