ET 08-0013, Response to Request for Additional Information Concerning the Results of the Fourteenth Steam Generator Tube Inservice Inspection

Response to Request for Additional Information Concerning the Results of the Fourteenth Steam Generator Tube Inservice Inspection

ML080660359
Person / Time
Site:	Wolf Creek
Issue date:	02/28/2008
From:	Garrett T Wolf Creek
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ET 08-0013, TAC MD5946
Download: ML080660359 (5)

Text

WQLF CREEK INUCLEAR OPERATING CORPORATION Terry J. Garrett Vice President, Engineering February 28, 2008 ET 08-0013 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Reference:

1)

Letter ET 07-0005, dated March 19, 2007, from T. J. Garrett, WCNOC, to USNRC

2)

Letter dated February 12, 2008, from B. K. Singal, USNRC, to R. A. Muench, WCNOC Docket No.

50-482:

Response to Request for Additional Information Concerning the Results of the Fourteenth Steam Generator Tube Inservice Inspection (TAC NO. MD5946)

Subject:

Gentlemen:

Reference 1 submitted the Steam Generator Tube Inspection Report in accordance with Wolf Creek Generating Station (WCGS) Technical Specification 5.6.10, "Steam Generator Tube Inspection Report." This report provided the results of the WCGS fourteenth steam generator tube inservice inspection.

Reference 2 provided a request for additional information (RAI) based on the Nuclear Regulatory Commission (NRC). staff review of Reference 1.

The Attachment provides Wolf Creek Nuclear Operating Corporation's responses to the questions in the RAI.

This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-4084, or Mr. Richard D. Flannigan at (620) 364-4117.

Since ;ely, JGarrett TJG/rlt Attachment cc:

E. E. Collins (NRC), w/a V. G. Gaddy (NRC), w/a B. K. Singal (NRC), w/a Senior Resident Inspector (NRC), w/a P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNVET

ý04 1

]

Attachment to ET 08-0013 Page 1 of 4 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING THE RESULTS OF THE FOURTEENTH STEAM GENERATOR TUBE INSERVICE INSPECTION Reference 1 submitted the Steam Generator Tube Inspection Report in accordance with Wolf Creek Generating Station (WCGS) Technical Specification 5.6.10, "Steam Generator Tube Inspection Report." This report provided the results of the WCGS fourteenth steam generator tube inservice inspection.

Reference 2 provided a request for additional information (RAI) based on the Nuclear Regulatory Commission (NRC) staff review of Reference 1. Provided below are Wolf Creek Nuclear Operating Corporation's responses to the questions.

1.

For each refueling outage or SG tube inspection since installation of the SGs, provide the cumulative effective full power months that the SGs have operated.

Response

Reference the following table that shows the cumulative effective full power months (EFPM) for each refueling outage that the WCGS steam generators (SGs) have been inspected.

Refueling Outaae Year EFPM 1984 PSI 0

1986 RF01 12.84 1988 RF03 29.16 1990 RF04 42.72 1991 RF05 57.36 1993 RF06 69.72 1994 RF07 84.84 1996 RF08 99.36 1997 RF09 116.76 1999 RF10 132.72 2000 RF11 149.04 2002 RF12 165.36 2003 RF13 182.64 2005 RF14 198.12 2006 RF15 214.68

2.

Provide a high-level summary of the results of the scale profiling analysis.

Response: During the 15 th Refueling Outage, an Advanced Scale Conditioning Agent (ASCA) maintenance cleaning was performed on SG "A" and "D".

A Scale Profiling Eddy Current analysis was performed to evaluate what the status of the deposit levels were in both spatial distribution and inventory estimates relative to the 1 3th Refueling Outage (the previous outage in which SG "A" and "D" were cleaned/inspected). This analysis consisted of three parts:

An analysis of the low frequency eddy current bobbin data Rotating Pancake Coil inspection of selected tube-tube support plate intersections to evaluate potential quatrefoil blockage Upper Bundle In-Bundle (UBIB) visual inspections

Attachment to ET 08-0013 Page 2 of 4 Some general observations from the analyses are:

1. The heaviest deposit levels are in a volume starting just below the 7th Tube Support Plate (Hot Leg) and progressing to the u-bend, Hot Leg side.

2. A concentration of scale buildup was observed between the top of the tubesheet and the flow distribution baffle in the cutout region.

3. In general, the morphology of the SG deposit patterns were remarkably consistent between SG "A" and "D" as well as that observed for SG "B" in the 14 th Refueling Outage.

4. The influence of the ASCA was clearly visible at all levels of the bundle. The overall deposit morphology was the same between pre and post-ASCA but the deposit levels were visibly reduced at all levels of the bundle.

5. Rotating Pancake Coil evaluation of the tube-tube support plate intersections revealed that deposit buildup was very low, posing no flowpath blockage. This was true even in areas where the freespan deposit level was relatively high.

6. Visual inspection of the upper bundle region confirmed the observations made by eddy current data analysis. While surface deposits were observed, and some spalling detected, the quatrefoil lands were essentially open.

7. Deposit inventories estimated were SG "A" -

1363 pounds and SG "D" 1225 Ibs, a difference of about 10%.

3.

Clarify the statement "100% of the U-bends have been inspected during the second inspection period." Does this mean that you were in the 90 effective full power month inspection period listed in your technical specifications? If so, when during the period were the U-bends for the tubes in rows I through 4 inspected?

Response: 100% of the u-bends in SG "A" and "D" have been inspected during the second inspection period (90 EFPM inspection period listed in Technical Specification 5.5.9).

In the 11 Refueling Outage (149.04 EFPM), bobbin inspections were performed in 100% of the u-bends in Rows 3 and 4 of SG "A" and "D". Also, plus-point inspections of 50% of the Row 1 and 2 u-bends were performed.

In the 13 th Refueling Outage (182.64 EFPM), bobbin inspections were again performed in 100% of the u-bends in Rows 3 and 4 of SG "A" and "D".

Plus-point inspections of 50% of the Rows 1 and 2 u-bends that were not previously inspected in the 11th Refueling Outage were performed.

4.

Describe the scope and results of any secondary-side inspections.

Response: Visual inspections on the secondary side of SG "A" and "D" were performed in the 15th Refueling Outage as follows with no significant findings noted:

Top of tubesheet cleanliness inspections -

Cleanliness inspections were conducted following the performance of sludge lancing in SG "A" and "D", and verified that the top of tube sheet was clean.

Attachment to ET 08-0013 Page 3 of 4 Top of tubesheet in-bundle inspections - A limited amount of top of tube sheet in-bundle inspections were performed. Although the inspection was limited, the information gathered in SG "A" and.",'D" in regions coincident-with those inspected in the 13 th Refueling Outage support the same behavior patterns of deposit growth and collaring as observed in the previous outage.

Upper bundle in-bundle inspections (UBIB) - UBIB video inspection was performed on both SG "A" and "D". The inspections of selected columns spanned the region from the top of tube support plate 3 to the bottom of tube support plate 7. The results of the UBIB inspections were similar between the two SGs, and the quatrefoil flow holes that were viewed were clear with no observed obstructions.

Foreign object search and retrieval (FOSAR) - FOSAR activities identified and removed some foreign objects from SG "A" and "D".

No potentially damaging foreign objects were observed at the accessible locations of the possible loose parts (PLPs), i.e.,

periphery and tube lane. Most of the foreign objects identified were benign items such as sludge rocks and scale, and were not retrieved. In SG "D", a pin thought to be from a failed upstream valve was located and removed. In SG "A", a very fine wire fiber on the periphery of the bundle was left in place. This type of item has very little potential for damaging tubes and is enveloped by prior analysis of foreign objects.

5.

On page 32 of 37 of March 19, 2008 [2007] letter, the indication in the tube in row 27, column 97 is listed as being 0.78 inches below the top of the tubesheet. Discuss the source and nature of this indication. Similarly, discuss the source and nature of the indication in the tube in row 21, column 117 which has an indication 0. 15 inches below the top of the tubesheet. If attributed to a loose part, discuss whether these tubes were expanded for the full length of the tubesheet (or whether there is a crevice at the top of the tubesheet).

Response

Note that the two indications documented above were previously discussed in responses to question 5 and question 6 in WCNOC letter ET 05-0013 (Reference 3).

Both of the indications were in SG "D" and were reported as volumetric indications at approximately the top of the tubesheet. These indications were also previously reported in the 13th Refueling Outage.

The indications were sized using the qualified technique of ETSS21998.1, with a maximum depth of 15% through-wall.

Since no foreign objects were reported at these locations, it is extremely unlikely that these are continuing wear sites. The apparent small increment in depth at the 15th Refueling Outage compared to 13th Refueling Outage is attributed to improved data quality and improved instrumentation in the 15 th Refueling Outage. Also, none of the indications were associated with a PLP indication, indicating that no foreign object currently resides at the location of these tubes. Since the indication sizes are less than the plugging limit of 40% through wall depth and have not changed since the prior inspection, the affected tubes were retained in service.

The apparent location of the indication in row 21 column 117, just below the top of the tubesheet, is most likely a reflection of the locating accuracy of the eddy current probe, but could also be in a crevice resulting from the tube expansion location normal tolerance. Prior studies have shown that the actual position of the expansion transition can vary by approximately 0.3 inches from the top of the tubesheet.

Thus, an apparent location of a volumetric indication below the top of the tubesheet can reasonably be anticipated.

Attachment to ET 08-0013 Page 4 of 4 A potential source of the indication in row 27 column 97 could be a geometric anomaly that occurred during the manufacturing such as expansion into a burr or undercut remaining from the tubesheet drilling process..Prior operating experience indicates that a volumetric indication can arise from expansion over a burr in the tubesheet bore. Similarly, expansion into a local undercut resulting from the tubesheet drilling process can be interpreted as a volumetric indication. Both conditions are benign.

The two tubes discussed above were expanded for the full length of the tubesheet.

The indications described above have been reported previously as volumetric indications with no apparent change between inspections.

Close analysis of the indications has not shown evidence that they are anything other than volumetric indications.

References:

1.

WCNOC letter ET 07-0005, "Results of the Fourteenth Steam Generator Tube Inservice Inspection," March 19, 2007.

2.

NRC letter, "Wolf Creek Generating Station - Request for Additional Information RE:

Review of Results of the 14 th Steam Generator Tube Inservice Inspection (TAC NO.

MD5946)," February 12, 2008.

3.

WCNOC letter ET 05-0013; "Wolf Creek Nuclear Operating Corporation's (WCNOC's)

Response to Request for Additional Information Regarding the Steam Generator Tube Inspection Summary Reports for the Fall 2003 Outage (TAC No. MC5022)," July 14, 2005.