Unterweser under scrutiny

1 January 2003

Unscheduled non-destructive examination (NDE) at E.ON's 1350MWe Unterweser has revealed cracks on three of the four steam generators at the intersection with the feedwater system, according to German regulators. State regulators said that the cracks would not have leaked or broken before the next scheduled NDE, and closer examination of the cracks, did not indicate serious problems. In addition, one official has suggested that what at first were classified as crack indications, may be only indentations on the surface. It is believed that the indentations were caused by corrosion, and that there was no evidence of faults during welding or component manufacture.

According to the Federal Ministry of Environment and Nuclear Safety (BMU), the indications are in the same area of all three steam generators. One crack indication, located on the inner surface of a feedwater pipe with a wall thickness of 30mm, was 260mm long and 2mm deep. It was located at the point where feedwater is injected into the steam generator, BMU said, "calling into question whether there would be sufficient coolant" in the case of a "large leak" in the tube.

According to Wolfgang Jüttner, chief regulator in Lower Saxony, the PWR has been offline since 4 September, when it was shut to replace the main electrical generator. The inspections of steam generator piping recently carried out were originally scheduled for the next routine refuelling and maintenance outage in early 2003.

The crack indications were found using ultrasound. According to the inspection schedule, every two years one of the steam generators is routinely inspected. When the steam generator that was due to be inspected in 2003 was inspected in autumn, it was found to exhibit cracks. Regulators then ordered inspections at the other three steam generators and found cracks at the feedwater nozzles in two of them.

Jüttner said there was no possibility that a leak in a tube or a break would have occurred before the next scheduled inspection.



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