Handover Omission During a Load-Following Maneuver
A control room is executing a planned power reduction from 100% to 70% for grid demand. The maneuver is routine and the outgoing shift lead gives a five-minute verbal handover in a noisy room while the incoming lead is still logging in. Key content: a boron dilution is in progress, one rod position indicator is unreliable, and a chemistry sample is pending. The outgoing lead mentions the dilution in passing but does not state its current rate or the target boron concentration. The incoming lead nods and says 'got it.' Two hours later the reactor operator notices the dilution has continued past the intended endpoint, and the boron concentration is below the value assumed in the maneuver procedure. No alarm annunciated because the deviation was within the analyzer's normal band. The shift log contains the words 'dilution ongoing' with no numbers.
1. Analyze the communication failure using a structured handover framework, identifying what was lost and why.
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Using a structured handover model (situation, background, assessment, recommendation), the handover failed at multiple points. Situation: the power maneuver was conveyed. Background: the unreliable rod indicator and pending chemistry sample were mentioned but their operational significance-that rod position feedback is degraded and chemistry confirmation is outstanding-was not made explicit. Assessment: the dilution rate, current boron concentration, and target endpoint were omitted entirely; these are the actionable numbers. Recommendation: no explicit statement of what the incoming lead must verify or when to stop the dilution. The environmental conditions-noise, simultaneous log-in, five-minute duration-guaranteed low retention. The incoming lead's 'got it' is a closed-loop acknowledgment without read-back, so the outgoing lead had no evidence of comprehension. The written log entry 'dilution ongoing' is a label, not a record; it cannot support reconstruction. The failure is a predictable consequence of unstructured verbal handover under time pressure, not carelessness by one person.
2. Propose a redesigned handover and a verification barrier that would have caught the over-dilution before it mattered.
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Redesign: a written handover card completed before the verbal exchange, covering active evolutions with quantitative parameters (dilution rate, current and target boron concentration, expected duration), open items with owners and deadlines, and known equipment degradations with their operational impact. The verbal handover should occur face-to-face in a quiet location, with the incoming lead reading back each active evolution and its stopping condition. A two-person rule for dilution: the reactor operator and a second licensed operator independently track the projected endpoint and compare at defined checkpoints (for example every 30 minutes or every 10% of the planned dilution). Add a calculated endpoint to the maneuver procedure with an explicit hold point requiring supervisor sign-off before crossing it. Since the analyzer's normal band masked the deviation, add an independent check-periodic manual computation of boron concentration from dilution flow and time-rather than relying on a single broad-band instrument. Finally, treat 'dilution ongoing' log entries as non-compliant and require numbers, so any subsequent shift can reconstruct the state without depending on memory.