A higher than foreseen boron concentration was dicovered on units B1 and B2 at Chinon NPP. This was due to a calibration error on the measuring device.
See next page for additional information.
BASIS FOR RATING: 1. Calibration error, 2. violation of the technical specifications during the dilution process, 3) Lack of feed-back of experience (same incident at Dampierre in 1991), 4) Common mode failure.
DIFFICULTIES IN RATING: No difficulties. table A1 - adequate - expected.
Event date: Mon, 16-09-1991