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FR-I.2 — Response to Low Pressurizer Level

CSF RCS inventory — ORANGE path. Entered when pressurizer level
drops toward the low-low setpoint or off-scale low (~14% indicated).
Loss of indicated level means loss of confirmation that RCS mass is
adequate; off-scale-low pressurizer is the precursor signature of
either an unidentified LOCA or an aggressive cooldown that has
contracted the RCS inventory faster than charging can compensate.

CSF: rcs-inventory

Step 1 verify-low-level

Check: pressurizer level «PZR-LVL» trending toward low-low setpoint (~14% indicated); charging flow «CHG-FLOW» at maximum demand; subcooling margin «SUB-MARGIN»; RCS pressure «PT-455» stable or decreasing
Caution: low pressurizer level during planned cooldown is expected — FR-I.2 entry is unexpected low level OR level dropping faster than cooldown alone explains
- Low level confirmed (level approaching low-low, charging at max demand) → #increase-makeup
Because: ORANGE-path action engages full inventory makeup
- Stabilized or recovering → E-0
Because: return to diagnostic flow

Step 2 increase-makeup

Within: 5 minutes — uncovering of pressurizer instruments means loss of level indication; corrective action is needed before that
Action: maximize charging flow «CHG-FLOW» — both charging pumps «CHG-PUMP-A» / «CHG-PUMP-B» running with control valve open as far as flow path allows
Action: isolate letdown «LET-FLOW» (close letdown isolation) to stop outflow
Action: verify SI status «SI-SIG» — if SI not active and conditions justify it (subcooling lost OR LOCA indicators present), actuate SI manually
Action: check RCS sample / inventory accounting for unexplained mass loss — small-break LOCA inside containment may not be obvious from instrumentation alone
Note: Vogtle UFSAR §15.5.1 (inadvertent letdown isolation failure) and §15.5.2 (inadvertent SI termination) are scenario references
- Pressurizer level recovering → #monitor
Because: makeup restored RCS inventory; transition to monitoring
- Level not recovering despite max charging → E-1
Because: LOCA management is required when makeup cannot keep up

Step 3 monitor

Check: pressurizer level «PZR-LVL»; RCS pressure «PT-455»; subcooling «SUB-MARGIN»; vessel level «RVLS-DYN» if indicated
Within: re-evaluate every 5 min during continued low-level recovery
- Pressurizer level back in normal band AND RCS pressure stable → E-0
Because: inventory CSF returned to GREEN
- Voiding evidence (subcooling lost OR RVLS dropping OR steam space in upper head expanding) → FR-I.3
Because: voids-in-vessel response handles the case where mass loss has progressed to voiding
- LOCA progressing despite makeup → E-1
Because: ongoing LOCA management

Tags

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

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

  • id: CHG-FLOW
    description: charging flow rate
    sim-path: cvcs.charging.flow
    units: gpm
    equipment: charging-system
    source: Vogtle UFSAR §9.3.4

  • id: LET-FLOW
    description: letdown flow rate
    sim-path: cvcs.letdown.flow
    units: gpm
    equipment: charging-system
    source: Vogtle UFSAR §9.3.4

  • 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: SI-SIG
    description: safety injection actuation signal (latched)
    sim-path: ess.si.actuation_signal
    units: bool
    equipment: si-system
    source: Vogtle UFSAR §6.3

  • 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: 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