This is a 4-hour report as required by
Technical Specification (TS) 5.5.9, Table 5.5.9-2, reported via the
ENS in accordance with
10 CFR 50.72(b)(3)(ii)(A), 'Any event or condition that results in the nuclear power plant, including its principal barriers, being seriously degraded'.
Greater than one percent of steam generator (SG) 1-1 and SG 1-2 tubes were determined to be defective and require plugging. Diablo Canyon performs 100% bobbin inspection of SG tubes, thus, no expanded bobbin inspection scope was required.
On November 11, 2005, during the Unit 1 thirteenth refueling outage (1R13), final analysis of eddy current data of SG 1-1 and SG 1-2 indicated that greater than one percent of the total tubes inspected in two SGs were defective placing them in Category C-3. Thirty seven (37) defective tubes in SG 1-1 and forty one (41) defective tubes in SG 1-2 were detected and are being plugged. Most of the pluggable indications are due to circumferential outside diameter stress corrosion cracking at the hot leg tube support plates and at the hot leg top of tubesheet. Results of SG tube inspections that fall into Category C-3, requires a 4-hour non-emergency report to accordance with Diablo Canyon TS 5.5.9, Table 5.5.9-2 and 'Notification to the NRC pursuant to 10 CFR 50.72(b)(2)' (a 4-hour requirement, replaced by 10 CFR 50.72(b)(3)(ii), now an 8-hour requirement).
An NRC teleconference in accordance with TS 5.6.10.d to report the preliminary SG tube inspection results was conducted on November 9, 2005, at 1100 PST.
A Special Report in accordance with TS 5.6.10.a to report the number of tubes plugged in each SG, and TS 5.6.10.c describing the cause of the tube degradation and corrective measures taken to prevent recurrence will be submitted prior to returning Diablo Canyon Unit 1 to power operation.
The licensee notified the NRC Resident Inspector.
