FR-C.1 — Response to Inadequate Core Cooling¶
CSF core cooling — RED path. Entered when core exit thermocouple
readings are saturated or superheated AND reactor vessel level
indication shows core partially uncovered, OR when ECCS flow blockage
prevents adequate heat removal during a LOCA. This is the most severe
challenge to core cooling and represents the entry to inadequate-core-
cooling territory (the regime that drove TMI-2 in 1979). Recovery is by
maximum SI flow combined with controlled RCS depressurization to widen
the SI injection window; if that fails, emergency feed-and-bleed via
PORVs becomes the last barrier before SAMG entry (Vogtle UFSAR §15.6.5
inadequate-core-cooling analysis).
CSF: core-cooling
Step 1 verify-icc¶
Check: core-exit thermocouples «CET-AVG» reading saturated (CET ≥ T_sat at «PT-455») OR superheated; reactor vessel level «RVLS-DYN» below the upper-head two-phase mixture level; subcooling margin «SUB-MARGIN» negative or zero
Caution: CETs reading high with normal pressurizer level may indicate a stuck-open PORV venting steam from the upper head — verify «PORV-456A» / «PORV-456B» status before declaring ICC
Note: TMI-2 lesson — operator must trust CET indications even when conflicting "normal" indicators are present
- Inadequate core cooling confirmed (CETs ≥ T_sat AND vessel level low AND no subcooling) → #maximize-si
Because: RED-path response is non-discretionary; speed of escalation matters
- Indications consistent with recovery (CETs decreasing, vessel level recovering, subcooling returning) → E-1
Because: return to LOCA flow; cooling has been re-established
Step 2 maximize-si¶
Within: 2 minutes of ICC confirmation — clad-temperature rise in uncovered fuel can reach 100 °F/min at decay-heat power
Action: verify ALL high-head SI pumps «SI-PUMP-A» / «SI-PUMP-B» running; verify charging pumps «CHG-PUMP-A» / «CHG-PUMP-B» in SI alignment
Action: ensure accumulators armed («ACCUM-1» / «ACCUM-2» / «ACCUM-3» / «ACCUM-4» discharge valves open, isolation valves open)
Action: depressurize RCS by opening pressurizer PORVs «PORV-456A» AND «PORV-456B» if RCS pressure exceeds high-head SI shutoff head (~1500 psig); this opens the injection window to accumulator (~600 psig) and low-head pumps (~200 psig)
Caution: rapid depressurization can worsen voiding in the upper head and may collapse the steam bubble that was previously stabilizing vessel level — coordinate with the shift supervisor; pressure should drop in a controlled manner, not free-fall
Note: per Vogtle UFSAR §15.6.5, the design-basis assumption is that all available SI pumps inject; manual alignment is the backup
- Core cooling restored (CETs subcooled, vessel level recovering, subcooling returning) → #verify-recovery
Because: maximum-SI response succeeded; proceed to recovery verification
- Maximum SI not restoring cooling within 5 minutes → #emergency-bleed
Because: feed-and-bleed is the last barrier before SAMG entry
Step 3 emergency-bleed¶
Within: 1 minute of #maximize-si failure recognition
Action: open BOTH PORVs «PORV-456A» AND «PORV-456B» fully (block valves «BLOCK-456A» / «BLOCK-456B» OPEN) and lock them open via control-room signal
Action: confirm full SI flow from RWST through all available paths into containment sump (feed phase via SI; bleed phase via PORVs venting to pressurizer relief tank, which ruptures its disc, delivering inventory to containment sump)
Action: verify containment sump «CTMT-SUMP-LVL» rising — confirms the bleed path is intact
Caution: feed-and-bleed at full SI + open PORVs consumes RWST inventory at ~3000 gpm; cold-leg recirculation transfer (ES-1.3) MUST be ready before RWST reaches low-low setpoint
Caution: this action is irreversible from a containment-cleanup standpoint — the entire RWST contents end up in containment sump; consequences are significant but inadequate core cooling consequences are worse
- Subcooling and vessel level recovering during feed-and-bleed → #verify-recovery
Because: feed-and-bleed succeeded; verify before declaring recovery
- Subcooling and vessel level NOT recovering after 10 minutes of feed-and-bleed → FR-C.2
Because: degraded-cooling response handles the slower-progression regime; if feed-and-bleed is partially effective the response may stabilize at ORANGE rather than RED
Note: if conditions degrade toward core damage indicators (CET superheat > 1200 °F, rapid vessel level decrease, hydrogen indications) the response transitions out of the EOP set into the SAMG (Severe Accident Management Guidance) procedure set — Vogtle SAMG entry conditions per WCAP-13914. This wiki does not yet hold SAMG content; flag for owner.
Step 4 verify-recovery¶
Check: core-exit thermocouples «CET-AVG» subcooled (CET < T_sat - 30 °F); reactor vessel level «RVLS-DYN» recovering; subcooling margin «SUB-MARGIN» ≥ 30 °F and increasing
Within: hold this step for at least 5 minutes of stable, improving trends before exit — premature exit risks oscillation back to RED
- All three indicators recovered AND stable for ≥5 minutes → E-1
Because: CSF core cooling restored to GREEN; LOCA flow at E-1 resumes
- One or more indicator not yet recovered → #maximize-si
Because: recovery incomplete; re-exercise maximum-SI before considering exit
Tags¶
-
id: CET-AVG
description: core-exit thermocouple average (5+ representative locations across the core)
sim-path: rcs.core_exit.thermocouple.avg
units: degF
equipment: rcs
source: Vogtle UFSAR §7.5 (CET system added per NUREG-0737 II.F.2) -
id: RVLS-DYN
description: reactor vessel level indication system, dynamic-pressure-compensated channel
sim-path: rcs.rvls.dynamic.level
units: percent_collapsed_liquid
equipment: rcs
source: Vogtle UFSAR §7.5 (RVLIS per NUREG-0737 II.F.2) -
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: 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: BLOCK-456A
description: pressurizer PORV 456A block valve position
sim-path: rcs.pressurizer.block.456a.position
units: enum[OPEN,CLOSED]
equipment: pressurizer
source: Vogtle UFSAR §5.4 -
id: BLOCK-456B
description: pressurizer PORV 456B block valve position
sim-path: rcs.pressurizer.block.456b.position
units: enum[OPEN,CLOSED]
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: CHG-PUMP-A
description: charging pump A status
sim-path: cvcs.charging_pump.a.status
units: enum[STOPPED,RUNNING,FAULT]
equipment: charging-system
source: Vogtle UFSAR §9.3.4 -
id: CHG-PUMP-B
description: charging pump B status
sim-path: cvcs.charging_pump.b.status
units: enum[STOPPED,RUNNING,FAULT]
equipment: charging-system
source: Vogtle UFSAR §9.3.4 -
id: ACCUM-1
description: accumulator tank 1 (cold-leg loop 1) discharge isolation
sim-path: ess.accumulator.1.discharge_valve
units: enum[OPEN,CLOSED]
equipment: si-system
source: Vogtle UFSAR §6.3.2 -
id: ACCUM-2
description: accumulator tank 2 (cold-leg loop 2) discharge isolation
sim-path: ess.accumulator.2.discharge_valve
units: enum[OPEN,CLOSED]
equipment: si-system
source: Vogtle UFSAR §6.3.2 -
id: ACCUM-3
description: accumulator tank 3 (cold-leg loop 3) discharge isolation
sim-path: ess.accumulator.3.discharge_valve
units: enum[OPEN,CLOSED]
equipment: si-system
source: Vogtle UFSAR §6.3.2 -
id: ACCUM-4
description: accumulator tank 4 (cold-leg loop 4) discharge isolation
sim-path: ess.accumulator.4.discharge_valve
units: enum[OPEN,CLOSED]
equipment: si-system
source: Vogtle UFSAR §6.3.2 -
id: CTMT-SUMP-LVL
description: containment recirculation sump level
sim-path: containment.sump.level
units: percent
equipment: containment
source: Vogtle UFSAR §6.2