Skip to content

Steam Generator Tube Rupture

Reactor at 100% rated thermal power; a complete double-ended rupture of a single SG-A steam generator tube develops at t = 0. Primary-to-secondary leakage drives SG-A level upward and slowly depressurizes the RCS. The crew enters E-0 on safety-injection actuation, recognises the ruptured SG signature at E-3#identify-ruptured-sg (rising SG-A level + air- ejector radiation rise + falling RCS pressure), and isolates SG-A per E-3#isolate-ruptured-sg before initiating cooldown and depressurization to terminate the leak at E-3#verify-leak-terminated. Recovery flows through ES-3.1 for backfill and stabilization.

The classifier surfaces this as Alert via the SA5 IC (RCS pressure crosses 1500 psig under continued leakage before the operator successfully depressurizes below the ruptured SG). A non-isolated SGTR would also trigger SA9 (containment-bypass radiation pathway), but for this scenario the air-ejector pathway is contained and CTMT-RAD does not rise.

Initial state

{
  "PT-455": 2235,
  "SG-A-LVL-NR": 50,
  "SG-B-LVL-NR": 50,
  "SG-C-LVL-NR": 50,
  "SG-D-LVL-NR": 50,
  "RCS-TEMP-HOT": 612,
  "SUB-MARGIN": 35,
  "RWST-LVL": 92,
  "AEJ-RAD": 10
}

Injections

[
  { "tag": "SG-A-LVL-NR", "value": 65, "at-time-s": 60 },
  { "tag": "AEJ-RAD", "value": 250, "at-time-s": 90 },
  { "tag": "PT-455", "value": 1700, "at-time-s": 180 },
  { "tag": "SG-A-LVL-NR", "value": 78, "at-time-s": 240 },
  { "tag": "PT-455", "value": 1420, "at-time-s": 600 }
]

Expected traversal

[
  "E-0#verify-reactor-trip",
  "E-0#verify-turbine-trip",
  "E-0#check-si-status",
  "E-3#identify-ruptured-sg",
  "E-3#verify-intact-sg-available",
  "E-3#isolate-ruptured-sg",
  "E-3#control-rcs-pressure",
  "E-3#initiate-cooldown",
  "E-3#depressurize-rcs",
  "E-3#verify-leak-terminated"
]

Expected terminal state

{
  "PT-455": 1420,
  "SG-A-LVL-NR": 78,
  "AEJ-RAD": 250
}

EAL classification

Alert (SA5) at t = 600 s — pressurizer pressure crosses 1500 psig under continued primary-to-secondary leakage. SU4 (RCS leakage) fires earlier at t = 180 s but is superseded. Air-ejector radiation rises visibly but stays below the CTMT-RAD SA9 threshold (which monitors containment, not the secondary radiation path — the SGTR-specific release path is via the ruptured SG to atmosphere via the ARV, not through containment).

References

  • Vogtle UFSAR §15.6.3 (steam generator tube rupture analysis)
  • NEI 99-01 SA5 (RCS depressurization)
  • Westinghouse-style ERG procedures E-0, E-3, ES-3.1