ML052560042
| ML052560042 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 04/01/2005 |
| From: | NRC/NRR/DE/EMCB |
| To: | Entergy Nuclear Generation Co |
| References | |
| Download: ML052560042 (2) | |
Text
SUMMARY
OF CONFERENCE CALL ARkANSAS NUCLEAR ONE, UNIT 2 ENTERGY NUCLEAR GENERATION COMPANY On April 1, 2005, the staff of the Materials and Chemical Engineering Branch (EMCB), Division of Engineering (DE), NRR, participated in a conference call with Entergy Nuclear Generation Company (the licensee) representatives regarding inspections being performed in the Arkansas Nuclear One, Unit 2 (ANO-2) steam generators (SGs) for loose parts and loose parts related damage to tubing. ANO-2 is a 2-loop Combustion Engineering plant with replacement SGs installed in Fall 2000 and employing Alloy 690 thermally treated tubing. ANO-2 was shutdown on March 8, 2005, due to primary to secondary leakage in the SG A, just one week prior to a refueling outage that was scheduled to commence on March 15, 2005. The leak was first reported on February 26, 2005 when the Nitrogen-1 6 (N-1 6) monitor reading rose above background level and increased to about 35 gallons per day (gpd) at the time the licensee elected to shutdown the unit.
One tube (71-69) was observed to be dripping under a static head on the hot leg side of SG A at the outer periphery. Eddy current testing revealed the leaker and 2 adjacent tubes to exhibit indications just above the tubesheet. Secondary side visual inspection revealed a piece of metal wedged among these tubes. This piece was removed and examined. The piece measured 1-3/8 inches long, 0.7 inches wide, and 1/4 inches thick and consisted of a heavily cold worked, low carbon steel. The licensee was unable to determine the source of this material.
The licensee performed a 50% sample, full length bobbin inspection of the tubing in both SGs and a 20% sample, +Point inspection at the top of the tubesheet (TTS), +/- 3 inches, in both steam generators. Both the bobbin and +Point samples were biased toward the periphery of the bundles. These inspections included 100% of the tubes in the peripheral zone, extending eight tubes in. Based on the finding of an additional volumetric indication in SG A located eight rows in from the periphery and just above the TTS, the licensee extend the zone of 100% inspection to 15 tubes in from the periphery in SG A. A total of 4 tubes in SG A and 1 tube in SG B were found with volumetric indications and were plugged. Of these, tubes with indications deeper than 40% were stabilized. An additional six tubes in SG B were found to contain possible loose part (PLP) indications. The licensee was unable to access the affected locations for visual inspection or loose parts retrieval. Because these tubes were located in relatively high cross flow locations, the licensee elected to plug and stabilize these tubes.
In addition to the foreign object found at the leaker location, secondary side visual examinations led to the finding and removal of additional foreign objects as follows:
ATTACHMENT
SG A
- 1 inch long piece of carbon steel
- one piece of weld wire
- one machine screw SGB
- small piece of machine winding Additional small foreign objects were identified, but could not be retrieved. These pieces were located in relatively low flow areas of the tube bundle and were determined by the licensee not to pose a concern with respect to tube damage potential during the upcoming cycle.
In-situ pressure testing was not discussed during the call since information on this testing was already provided by the NRC resident inspector. The leaking tube (71-69) was in-situ pressure tested prior to its being plugged and stabilized. The leaking tube was successfully tested to 3 times normal operating pressure (3900 psi x 1.15 = 4485 psi to adjust for temperature). Leakage at normal operating pressure (1300 psi x 1.15) was measured to be 0.3702 gpm (about 53 gpd) which, in the staff's opinion, is reasonably consistent with the 37 gpd measured by the N-1 6 monitor prior to plant shutdown. Leakage under main steam line break pressure (2560 psi x 1.15) was measured as 0.044 gpm, well within the 1 gpm allowed.
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