Time-pressure profile — LOCA¶
Operator workload and decision tempo during a LOCA evolve sharply across the first two hours. The crew's cognitive bandwidth budget is reset by each transition. EOP authoring assumes this profile; training validates against it.
Phase 0–5 min — recognition + automatic protection¶
- Crew load: maximum. Reactor trip + SI just actuated; control room alarms cascading; multiple parameters changing simultaneously.
- Decisions made: verify trip + turbine trip occurred (E-0 steps 1–2); verify AC electrical alignment (step 3); verify SI actuation (step 4); identify event class (LOCA vs faulted SG vs SBO).
- Failure modes most likely: slips (wrong-switch errors in rapid manipulation), lapses (skipped verify step). Mistakes are rare here because the team is following a heavily trained checklist.
- HF concerns: alarm load saturates working memory. The team relies on the procedure structure to deliberately filter what matters.
Phase 5–30 min — diagnosis + initial response¶
- Crew load: high but more structured. E-0 transitions to a specific E-series procedure (E-1 for LOCA, E-2 for steam-line break, E-3 for SGTR). Recovery flow begins.
- Decisions made: classify break size (small vs large vs outside containment); evaluate RCP-trip criterion; verify ECCS flow; assess containment status.
- Failure modes most likely: mistakes. The diagnostic questions are non-trivial; the team is past the checklist phase and into evaluating evidence.
- HF concerns: confirmation bias on the early diagnosis. Symptoms may evolve away from the initial hypothesis; the team must remain open to re-classifying.
Phase 30–120 min — recovery + transition¶
- Crew load: declining. SI is stable; the team works through the ES-series recovery (ES-1.1, ES-1.2, ES-1.3 for cold-leg recirculation transfer).
- Decisions made: RWST level monitoring; recirculation transfer; long-term cooldown planning; emergency response organisation coordination; EAL classification updates.
- Failure modes most likely: violations (perceived time available encourages cutting corners); lapses on coordination tasks. The acute phase is over but vigilance must hold.
- HF concerns: vigilance erosion. Crew rotation may begin for events extending into the second shift.
Procedures by phase¶
| Phase | Active procedure(s) |
|---|---|
| 0–5 min | E-0 |
| 5–30 min | E-1 (for LOCA), with FR-x branches as needed |
| 30–120 min | ES-1.1 / ES-1.2 / ES-1.3 / ES-1.4 |
| Beyond | recovery to cold shutdown via shutdown cooling |