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Event Report Forms (ERFs) are filed to the IAEA. Sometimes there are multiple event reports, updating the rating, the event description. Here you only see the latest event report

ERF send date: Thu, 16-10-1997
ERF description: On 1997-01-16, Pt Lepreau shutdown from full power to find the source of leakage of about 20 kg/hr D2O from the Primary Heat Transport )PHT) System, which had increase from a rate of 1 kg/hr over the period of a month. A leak search the next day found the source to be a crack at the first elbow on the outlet feeder pipe from fuel channel S08. The failure mode was determined to be strain rate induced corrosion cracking (SICC), initiated by a combination of chemical and mechanical stressors. The mechanical stressor was the failure to re-lock S08 on the East end, following work in changing the locked-ends of all channels during the 1995 outage. This failure permitted the channel to move by about 12-16 mm when engaged by the fuelling machine, and thus transmitted stress and strain to the outlet feeder which was sufficient to promote SICC. As part of the assessment of the safety significance of the crack, a preliminary Leak Before Break analysis indicated that a crack consistent with a leak rate of 500 kg/hr would need to exist before the structural integrity of the feeder assembly would be in jeopardy.
Basic rating: Level 0 from Table II - Degradation of Defence in depth - occurrence of an "expected" initiator (reactor coolant leakage which would not prevent controlled reactor shutdown and cooldown) with "full" safety function availability, uprated to level 1 due to inadequate procedures/QA to ensuring channel locking (root cause of the leakage) and failure of surveillance program to discover the unlocked channel.
ERF rating date: 03-03-1997
ERF contact person: Mr. W. Andersen
ERF address: 700 University Avenue, Canada
ERF affiliation: Ontario Hydro H11-B1, Nuclear Technology Services Division

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