ML083180783

Summary of Conference Call Regarding Fall 2008 Steam Generator Tube Inspections

ML083180783
Person / Time
Site:	Byron
Issue date:	11/20/2008
From:	David M Plant Licensing Branch III
To:	Pardee C Exelon Nuclear
david marshall NRR/DORL 415-1547
References
TAC MD9590
Download: ML083180783 (6)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 20, 2008 Mr. Charles G. Pardee President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NO.2 -

SUMMARY

OF CONFERENCE CALL REGARDING FALL 2008 STEAM GENERATOR TUBE INSPECTIONS (TAC NO. MD9590)

Dear Mr. Pardee:

On October 14, 2008, the Nuclear Regulatory Commission (NRC) staff participated in a conference call with Byron Station, Unit No.2 representatives regarding the ongoing steam generator (SG) tube inspection activities conducted during the fall 2008 refueling outage. The NRC staff follows the results of the industry's SG inspections in order to maintain an awareness of the condition of the SGs and the types of tube degradation mechanisms that are active.

The enclosed summary of the conference call is being provided to Exelon Generation Company, LLC for information. If there are any questions, please contact me at 301-415-1547.

Sincerely,

/}'b&(i~ i'~i~1 ()

Mv ~all J.

Plr~~

iL David, . lor Licensing Branch 111-2 jeel Manager Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-455

Enclosure:

Conference Call Summary cc w/encls: Distribution via ListServ

SUMMARY

OF CONFERENCE CALL WITH BYRON STATION, UNIT NO.2 REGARDING FALL 2008 STEAM GENERATOR TUBE INSPECTIONS On October 14, 2008, the Nuclear Regulatory Commission (NRC) staff participated in a conference call with Byron Station (Byron), Unit NO.2 representatives regarding the ongoing steam generator (SG) tube inspection activities conducted during the fall 2008 refueling outage (RFO).

Byron, Unit NO.2 has four Westinghouse Model D5 SGs, which are designated 2A through 2D.

All four SGs were inspected during th,e 2008 inspection. Each SG has 4,570 thermally-treated Alloy 600 tubes with an outside diameter of 0.750 inches and a nominal wall thickness of 0.043 inches. The tubes are hydraulically-expanded for the full-depth of the tubesheet at each end.

The tubes are supported by Type 405 stainless steel support plates with quatrefoil-shaped holes. The U-bend region of the tubes installed in rows 1 through 9 was thermally-treated after bending in order to reduce stress. The hot leg operating temperature is approximately 611°F.

Information provided by the licensee is summarized below.

At the time of the outage, the SGs have operated for approximately 18.6 effective full power years and have operated 88.6 effective power months (EFPM) in the second sequential (90 EFPM) inservice inspection (lSI) period.

At the time of the conference call, the lSI was approximately 70 percent complete (analyzed).

There was no primary to secondary leakage observed; therefore, no secondary side pressure tests were scheduled to be conducted.

There were no exceptions taken to industry guidelines.

The inspection scope for this outage is:

100 percent of the tubes in all four SGs were to be inspected with a bobbin probe except for the U-bends in the row 1 and row 2 tubes.

25 percent of the U-bends in the row 1 and row 2 tubes were to be inspected with a +PoinFM probe.

20 percent of the full tubesheet was to be inspected with a -Point'" probe from the tube end to 3 inches above the top of the tubesheet.

20 percent of the hot-leg bulges and over expansions were to be inspected with a

+PoinFM probe.

25 percent of the dents and dings in the hot leg that were greater than 3 volts were to be inspected with a -Point" probe.

Enclosure

-2 20 percent of the preheater baffle plate expansions were to be inspected with a

+PoinFM probe.

100 percent of the plugs on the hot leg and cold leg were visually inspected.

Each plug was captured on video and the condition assessed. None of the plugs were leaking. All plugs were verified to be installed.

The scope of inspection was in accordance with the Electric Power Research Institute guidelines, Revision 7.

The licensee indicated that they were on track for completing 100 percent of the tube inspections during the 90 EFPM inspection period. The licensee clarified that 100 percent of some locations may not have been examined, and the number of locations examined were prorated based on when the location was considered susceptible to flaws.

On the secondary side:

All four SGs were to be sludge lanced.

Foreign object search and retrieval (FOSAR) was to be perfomed on all four SGs at the secondary face of the tubesheet and the flow distribution baffle.

In SG 2C, an upper bundle, in-bundle inspection was to be conducted on support plates 8 and 11.

In SG 28, FOSAR was to be conducted on the preheater baffle plate since, historically, foreign objects collect there.

A visual inspection was to be conducted on SG 28's waterbox region including the target plate, distribution ribs, and cap plate.

The results of the inspection at the time of the call were:

Inspections detected 890 anti-vibration bar (AV8) wear indications. The percentage through wall degradation ranged from 85 to 40 percent, and only one tube (with degradation measuring 40 percent through wall) in SG 2A was scheduled to be plugged.

Inspections for preheater wear were still in progress at the time of the call, and 16 historical indications were being tracked.

With respect to wear from foreign objects:

There were two new indications at a support plate in SG 28 attributed to foreign object wear:

-3 One of these new indications was attributed to a historical object (first discovered in Cycle 5) that was not retrievable. This object caused a 15 percent through wall flaw and two tubes with possible loose part indications. All three tubes were scheduled to be stabilized and plugged.

The other new indication measured 38 percent through wall. The object was trapped in a quatrefoil flow hole. This tube was scheduled to be stabilized and plugged.

Three historical indications attributed to foreign objects that had been removed in RFO 11 were also detected. There was no significant change in size of these indications since the previous inspection.

The inspection of 20 percent of the hot-leg tubesheet region was 98 percent complete. There were 44 tubes with axial primary water stress corrosion cracking indications in the bottom 0.2 inches of the tube. There was no circumferential cracking. As a result of finding these indications, the inspection was expanded to include 100 percent of the hot-leg tube ends and 20 percent of the cold-leg tube ends from the tube end to 2 inches above the tube end. At the time of the call, 55 percent of the hot-leg tube ends and 12 percent of the cold-leg tube end inspections were complete. No indications were found on the cold leg.

No in situ pressure testing was scheduled to be conducted.

No removal or pulling of the tubes was planned.

Inspection of the U-bend region of the row 1 and 2 tubes and the baffle plate expansions had not been performed at the time of the call.

Based on the results to date, five tubes were scheduled to be plugged: one in SG 2A due to AVB wear and four in SG 2B due to wear attributed to loose parts or due to the presence of a possible loose part.

Visual inspection summary:

Nine foreign objects were found on the top of the tubesheet. One was found in SG 2B and eight in SG 2C. The visual inspection of SGs 2A and 2D had not been conducted at the time of the call. Three objects retrieved were wires that measuring 0.02 to 0.14 inches in diameter and 0.5 to 0.75 inches long. There was no tube damage from these wires. None of the objects on the top of the tubesheet resulted in tube damage.

In SG 2B, at the preheater, nine objects were found which included gasket material, bristle wires, and one that may be attributed to hard sludge. A -Point'"

probe inspection was scheduled to be conducted in the tubes around these objects to identify wear that may have occurred as a result of these objects. The preheater visual inspection was still in progress at the time of the call.

-4 A visual inspection in SG 2C near an object that previously caused wear was performed. The tubes associated with this object were stabilized and plugged in a previous outage. The object was on the 8th hot-leg tube support. In the last outage, the licensee was not able to access the object. During, this outage, they gained access and the object was determined to be weld slag measuring approximately 0.5 inches in diameter and 2 inches long. The weld slag could not be removed. All tubes around the plugged tubes were inspected with a +PoinFM probe at the 8th tube support plate. No evidence was detected that the part had moved. Subsequent to the phone call, the licensee indicated that they determined that the object had moved slightly; therefore, three additional tubes were preventatively stabilized and plugged. No additional tube damage was caused as a result of the movement.

In SG 2C, deposit loading was assessed at the 11th tube support plate. At the 11th tube support, the tube lane and four columns in the bundle were inspected.

There was light to moderate loading of deposits. The deposit loading was consistent with prior outages.

Only cracks near the tube ends were found and dispositioned in accordance with the Byron technical specifications.

The tubes with the eddy current offset were inspected full length in the tubesheet on the hot-leg from 3 inches above the top of the tubesheet to the hot-leg tube end with a

+PoinFM probe. In addition, all hot-leg dents/dings greater than 3 volts and all indications attributed to AVB wear were inspected with a +PoinFM probe in these tubes.

The SG inspections and repairs were scheduled to be complete on October 16, 2008.

The NRC staff did not identify any issues that required follow-up action at this time; however, the NRC staff asked to be notified in the event that any unusual conditions were detected during the remainder of the outage.

November 20, 2008 Mr. Charles G. Pardee President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NO.2 -

SUMMARY

OF CONFERENCE CALL REGARDING FALL 2008 STEAM GENERATOR TUBE INSPECTIONS (TAC NO. MD9590)

Dear Mr. Pardee:

On October 14, 2008, the Nuclear Regulatory Commission (NRC) staff participated in a conference call with Byron Station, Unit No.2 representatives regarding the ongoing steam generator (SG) tube inspection activities conducted during the fall 2008 refueling outage. The NRC staff follows the results of the industry's SG inspections in order to maintain an awareness of the condition of the SGs and the types of tube degradation mechanisms that are active.

The enclosed summary of the conference call is being provided to Exelon Generation Company, LLC for information. If there are any questions, please contact me at 301-415-1547.

Sincerely, IRA!

Marshall J. David, Senior Project Manager Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-455

Enclosure:

Conference Call Summary cc w/encls: Distribution via ListServ DISTRIBUTION:

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