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FR-H.3 — Response to Steam Generator High Level

CSF heat sink — YELLOW path. Entered when any SG narrow-range
level exceeds the high-high alarm setpoint (typically 78% NR per Vogtle
Tech Spec). Three distinct causes drive this entry, each with a
different response: (1) AFW overfeed during recovery, (2) SGTR — rising
level from primary-to-secondary leak inventory, or (3) main feedwater
control failure. Identification of cause determines the correct
response — wrongly classifying SGTR as overfeed and stopping AFW would
remove a heat sink during ongoing radiological release.

CSF: heat-sink

Step 1 verify-high-level

Check: SG narrow-range levels «SG-A-LVL-NR» / «SG-B-LVL-NR» / «SG-C-LVL-NR» / «SG-D-LVL-NR»; identify which SG(s) above high-high setpoint
- High-high level confirmed on one or more SGs → #identify-cause
Because: YELLOW-path entry — must identify cause before action
- Level dropped below setpoint, transient resolved → E-0
Because: false-alarm or transient; return to diagnostic flow

Step 2 identify-cause

Decision: identify the cause of high SG level
1. AFW or main feedwater overfeed — flow indication shows continued feeding when level is rising; check «AFW-A-CV» / «AFW-B-CV» / «AFW-C-CV» / «AFW-D-CV» control-valve positions and AFW pump status «AFW-PUMP-A» / «AFW-PUMP-B» / «AFW-PUMP-T»
2. SGTR — affected SG also shows elevated N-16 «SG-A-N16» / «SG-B-N16» / «SG-C-N16» / «SG-D-N16» radiation; level rises despite isolated feedwater
3. Main feedwater control valve stuck open or oscillating — controller signal mismatch with valve position; isolate and place on manual
Caution: stopping AFW to an SG suspected of SGTR is wrong — leave AFW alignment in place until SGTR is ruled out
- AFW or main feedwater overfeed → #stop-overfeed
Because: corrective action is to throttle or stop the offending feed
- SGTR indications (elevated N-16 plus rising level on the same SG) → E-3
Because: full SGTR response, not isolated overfeed
- Cause not clear; treat as overfeed until proven otherwise → #stop-overfeed
Because: defensive action — slows level rise; SGTR diagnosis continues in parallel

Step 3 stop-overfeed

Action: throttle AFW control valve to affected SG («AFW-A-CV» as identified); place main feedwater controller on MANUAL and reduce demand
Within: 5 minutes — SG overfill into the steam line causes water-induced damage to the main steam piping and MSIV seats
Caution: do not stop AFW entirely on a single SG without verifying the other SGs are absorbing decay heat — partial AFW reduction is preferable to full isolation
Note: high-high SG level on multiple SGs simultaneously is unusual and suggests a common-cause AFW control failure
- SG level stable or decreasing toward normal band → E-0
Because: high-level controlled; return to diagnostic flow
- Cannot stabilize level (continues rising despite reduced feed) → FR-H.5
Because: low-level response handles the converse case; if level is uncontrollable in both directions a SGTR is increasingly likely — see Note above

Tags

  • id: SG-A-LVL-NR
    description: SG-A narrow-range level
    sim-path: secondary.sg.a.level_nr
    units: percent
    equipment: sg-a
    source: Vogtle UFSAR §10.3

  • id: SG-B-LVL-NR
    description: SG-B narrow-range level
    sim-path: secondary.sg.b.level_nr
    units: percent
    equipment: sg-b
    source: Vogtle UFSAR §10.3

  • id: SG-C-LVL-NR
    description: SG-C narrow-range level
    sim-path: secondary.sg.c.level_nr
    units: percent
    equipment: sg-c
    source: Vogtle UFSAR §10.3

  • id: SG-D-LVL-NR
    description: SG-D narrow-range level
    sim-path: secondary.sg.d.level_nr
    units: percent
    equipment: sg-d
    source: Vogtle UFSAR §10.3

  • id: AFW-A-CV
    description: SG-A AFW control valve position
    sim-path: afw.a.cv_position
    units: percent
    equipment: afw-system
    source: Vogtle UFSAR §10.4.9

  • id: AFW-B-CV
    description: SG-B AFW control valve position
    sim-path: afw.b.cv_position
    units: percent
    equipment: afw-system
    source: Vogtle UFSAR §10.4.9

  • id: AFW-C-CV
    description: SG-C AFW control valve position
    sim-path: afw.c.cv_position
    units: percent
    equipment: afw-system
    source: Vogtle UFSAR §10.4.9

  • id: AFW-D-CV
    description: SG-D AFW control valve position
    sim-path: afw.d.cv_position
    units: percent
    equipment: afw-system
    source: Vogtle UFSAR §10.4.9

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

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

  • 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: SG-A-N16
    description: SG-A main steam line N-16 radiation monitor
    sim-path: rad.msl.a.n16
    units: cps
    equipment: sg-a-msl
    source: Vogtle UFSAR §11.5

  • id: SG-B-N16
    description: SG-B main steam line N-16 radiation monitor
    sim-path: rad.msl.b.n16
    units: cps
    equipment: sg-b-msl
    source: Vogtle UFSAR §11.5

  • id: SG-C-N16
    description: SG-C main steam line N-16 radiation monitor
    sim-path: rad.msl.c.n16
    units: cps
    equipment: sg-c-msl
    source: Vogtle UFSAR §11.5

  • id: SG-D-N16
    description: SG-D main steam line N-16 radiation monitor
    sim-path: rad.msl.d.n16
    units: cps
    equipment: sg-d-msl
    source: Vogtle UFSAR §11.5