ES-1.2 — Post-LOCA Cooldown and Depressurization¶
Entered from E-1 or ES-1.1 when post-LOCA cooldown to RHR
conditions (Mode 4, ~350 °F, ~390 psig per Vogtle Tech Spec) is
required to enable RHR cut-in or to support a repair / refueling
outage. Manages residual SI flow (if still in service) while
controlling cooldown rate against PTS limits and depressurization
against subcooling-margin loss.
CSF: core-cooling
CSF: rcs-integrity
CSF: rcs-inventory
Step 1 verify-cooldown-conditions¶
Check: RCS conditions stable post-LOCA — subcooling margin «SUB-MARGIN» ≥ 30 °F sustained; pressurizer level «PZR-LVL» on-scale and controlled; SG levels controlled with AFW or MFW; at least 2 intact SGs available for heat removal
- All cooldown prerequisites met → #initiate-cooldown
Because: ready to begin cooldown
- Any condition not met → E-1
Because: continue LOCA management until cooldown prerequisites are stable
Step 2 initiate-cooldown¶
Within: cooldown is multi-hour; the criterion is RATE not duration
Action: align steam dump from intact SGs to condenser (if available) or atmospheric relief; control cooldown rate via «STEAM-DUMP» modulation
Action: maintain RCS pressure / level via charging «CHG-FLOW» and pressurizer heaters «PZR-HTR»
Action: continue SI flow if any of the four SI-termination criteria are still not met; terminate SI per ES-1.1 only when all four are simultaneously satisfied for ≥5 min
Caution: maximum cooldown rate is 100 °F/hr per Vogtle Tech Spec 3.4.3 below 350 °F; do NOT exceed even briefly — PTS limit curves use this rate as design-basis
Caution: cooldown rate of 100 °F/hr is the ABSOLUTE LIMIT; target operation at 50 °F/hr or slower to maintain PTS margin
- Cooldown progressing within Tech Spec, RCS conditions stable → #depressurize
Because: cooldown control established; proceed to controlled depressurization
- Heat sink degraded during cooldown (AFW lost OR steam release path lost) → FR-H.1
Because: heat-sink response required; cooldown cannot continue without it
Step 3 depressurize¶
Action: depressurize RCS toward RHR cut-in pressure (~390 psig) using pressurizer normal spray (if RCPs running) OR auxiliary spray (RCP-tripped) OR PORVs «PORV-456A» / «PORV-456B» (last resort)
Within: depressurization rate must not exceed PTS limit — track «TE-411-COLD» / «PT-455» trajectory continuously
Caution: depressurization with cold-leg-injection still active causes upper-head void formation as pressure drops below the upper-head saturation point; verify head-vent path available via FR-I.3 alignment before significant depressurization
- RHR cut-in conditions reached (RCS pressure ≤ 390 psig, Tcold ≤ 350 °F) → #transfer-to-recirc
Because: ready to align RHR for long-term cooling
- PTS limit being approached (trajectory crossing curve) → FR-P.1
Because: PTS RED-path response interrupts depressurization
Step 4 transfer-to-recirc¶
Check: RWST level «RWST-LVL» trend; remaining usable RWST inventory
- RWST approaching low-low setpoint → ES-1.3
Because: cold-leg recirculation transfer required to maintain SI from sump
- RWST adequate AND cooldown complete → END
Because: post-LOCA cooldown succeeded without recirculation transfer; transfer to Operations cold-shutdown procedures
- RWST adequate AND cooldown not yet complete → #initiate-cooldown
Because: continue cooldown loop until cut-in conditions reached
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: PZR-HTR
description: pressurizer heater bank energization status
sim-path: rcs.pressurizer.heaters.status
units: enum[OFF,ON,FAULT]
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: 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: CHG-FLOW
description: charging flow rate
sim-path: cvcs.charging.flow
units: gpm
equipment: charging-system
source: Vogtle UFSAR §9.3.4 -
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: RWST-LVL
description: refueling water storage tank level
sim-path: rwst.level
units: percent
equipment: rwst
source: Vogtle UFSAR §6.3.2