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CRACKS IN THE REACTOR CORE SHROUD IN THE LID OF THE SHROUD AND IN REACTOR VESSEL INTERNALS

A major overhaul was made during the past two years at Oskarshmn-1. Visual and ultrasonic testing revealed cracks in the core shroud and in some connected components and also in the feed water riser pipe.
Based on metallurgical tests and inspections the failure mechanism was determined as thermal fatigue.
The oxidation found in the end of the cracks indicate that the propagation had stopped. Stress calculations show that none of the cracks will grow to critical length at least within five years.
Corrective actions. The shroud support stand and feed water riser pipe have been replaced. Ends of cracks were taken away by electro discharge machining to prevent continued propagation. Inspections and tests will be performed annually.

Location: OSKARSHAMN-1
Event date: Sun, 01-01-1995
Nuclear event report
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