ML023470308

Steam Generator Inservice Inspection, Steam Generator Tube Plugging & Repair 30-Day Report

ML023470308
Person / Time
Site:	Oconee
Issue date:	12/05/2002
From:	Rosalyn Jones Duke Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML023470308 (7)

Text

SDuke R.A.JONES Or Power. Vice President A Duke Energy Company Duke Power 29672 / Oconee Nuclear Site 7800 Rochester Highway Seneca, SC 29672 864 885 3158 864 885 3564 fax December 5, 2002 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555-0001

Subject:

Oconee Nuclear Station, Unit 2 Docket No. 50-270 Steam Generator Inservice Inspection Steam Generator Tube Plugging and Repair 30-day Report As required by Technical Specification 5.6.8.a, this letter provides the number of tubes plugged or repaired during the Steam Generator (SG) Tube Inservice Inspection for the Unit 2 Cycle 19 refueling outage. In addition to the above information, the enclosure provides information requested by members of the Staff in a conference call on October 30, 2002.

One hundred percent (100%) of the Unit 2 SG Tubes were inspected with bobbin coil eddy current testing (ECT) probes, and tubes with indications were subsequently inspected with Motorized Rotating Pancake Coil (MRPC) probes.

There were no tubes repaired by sleeving in either steam generator. There were some tubes repaired by reroll in the upper tubesheet of Steam Generator B. The tables below identify the number of tubes removed from service by plugging and the number of tubes repaired by rerolling in the upper tubesheet.

Steam Generator Number of Tubes Pluggqed A 414- for ECT indications 16 - to capture non-stabilized plugged tube locations B 544- for ECT indications 16- to capture non-stabilized plugged tube locations Steam Generator Number of Tubes Rerolled A 0 B 38 (34 of these remain in service, 4 were plugged).

www. duke-energy.corn

USNRC Document Control Desk Page 2 December 5, 2002 Ifthere are any questions you may contact R. C. Douglas at (864) 885-3073.

V rly Yours,

. Jonyes Site Vice President Oconee Nuclear Station Enclosure cc: Mr. L. A. Reyes Regional Administrator, Region II Mr. M.C. Shannon Senior Resident Inspector Mr. L. N. Olshan ONRR, Senior Project Manager Mr. V. R. Autry DHEC

US NRC Document Control Desk Page 1 December 5, 2002 ENCLOSURE Oconee Nuclear Station, Unit 2 Summary Response to Request for Information NOTE: The following is a summary of a conference call discussion between the NRC Staff and Duke Energy Corporation on October 30,2002. The numbered items in bold are information requests provided in an NRC letter to Duke Energy Corporation dated September 13, 2002.

1. Discuss any primary to secondaryleakage prior to shutdown.

Response: Primary to secondary leakage prior to shutdown was < 0.5 GPD.

2. Discuss results of secondaryside pressure tests.

Response: No secondary side pressure tests were conducted.

3. Providegeneraldescription of areasexamined,Includingexpansion criteria,type of probe's used. Discuss inspection of the tube within the tubesheet, particularly the portion below the expansion/ransitionregion.

Response: The inspection scope is shown on Attachment A to this enclosure. The expanded region of the tube is inspected with qualified Plus-Point from the roll transition to the tube end.

4. Discuss the actions taken in response to Framatome'snotification of the effect of tubesheet hole dilationon the service life of B&W welded plugs.

Response: Framatome ANP analyzed the allowed heatup/cooldown cycles for each plug type. It was verified that the service life limits would not be exceeded prior to SG replacements, which are scheduled for the next refueling on each unit. All repair products used, except those listed below, are fully qualified for original 40 year operating life.

Plug TvDe # Pluas Allowed Cycles Current Cycles OEM Welded Plugs 16 205 120 Remote Welded Plugs 52 33 13 Taper Welded 13 205 74 In addition, each welded plug was visually inspected for any signs of leakage or cracking. No leakage or cracking was identified.

USNRC Document Control Desk Page 2 December 5, 2002

5. Describe the Inspection/pluggingplans with respect to Industry Identified severed tube Issue.

Response: All plugged tubes that met the following criteria with rolled plugs in the primary inlet, were removed, tube dewatered if necessary, and then inspected and replugged.

a. Tubes with a rolled plug in the primary inlet tubesheet that were replaced without being dewatered and also having a welded plug in primary outlet.

b. Tubes with an 1-600 rolled plug inlet and having a repair welded plug in primary outlet.

c. Tubes with rolled plug replaced in the inlet and having an explosive plug in outlet.

d. Tubes with ribbed plugs in the inlet that had been replaced with 1-690 rolled plugs without being dewatered and also having a ribbed plug in primary outlet.

e. Tubes with rolled plugs in the inlet that had been replaced that also had an original plug in the outlet.

Deplugging Results:

A OTSG 13 Removed None found with water in tube.

B OTSG 25 Removed 4 water < 70% 1 water >70%*

Tube B 32-8 water level was 87% and was swollen by approx. 0.030" to 0.040" along entire length of tube. This tube was initially plugged in 1993. The primary inlet plug was found missing in 1994. The cause of the missing plug was an installation torque issue. The inlet plug was replaced without dewatering in 1994. Tube B 31-7, immediately downstream, did not show indications of wear and eddy current verified that tube B 32-8 was not severed. Tube B 32-8 was replugged with a full length stabilizer installed.

A&B OTSG Eleven (11) tubes have welded or ribbed plugs in the inlet that are very difficult to remove. These tubes were captured by surrounding with stabilized plugged tubes in flow direction.

6. Provide summary of number of Indicationsto date of each degradationmode and axial location. Provide voltage, depth and length for most significant.

Response: The number of tubes plugged for each category is shown below:

USNRC Document Control Desk Page 3 December 5, 2002 2A OTSG 2B OTSG Capture Locations 16 16 Tube Defects 414 522 IGA 7 10 Wear 1 0 Freespan SCC/IGA 380 491 RoilTransition PWSCC 12 9 Impingement 0 1 Dent SCC 0 8 Misc. 8 3 Dent/Vol. Combination 6 22 Total Plugged - EOC-19* 430 560 Total Cumulative Plugged 1,300 1,688 8.4% 10.9%

• End-Cycle 19 Details of the depth, length and voltage will be provided in the report of inspection findings required by Technical Specification 5.6.8, b three months following completion of the inspection.

7. Describe the repair/pluggingplans for SG tubes that meet the repair/plugging criteria.

Response: For hot leg roll transitions that meet criteria for reroll repair, rerolls will be performed and the tube left in service. For all other degradation that meets the plugging criteria, the tube will be removed from service by installation of 1-690 rolled plugs in inlet and outlet.

Reroll repairs A OTSG: 0* B OTSG: 38

• <10 locations identified for reroll repair, tubes were plugged and included in the response for the above item 6.

8. Discuss the previous history of SG tube inspection results, includingany "look backs" performed for significantindicationswhere used for dispositioning (MBM's)

Response: All bobbin indications will receive a Plus-Point exam and are dispositioned based on this result. Past history bobbin data is not used to determine special interest locations for augmented inspections (i.e., plus point exam),

USNRC Document Control Desk Page 4 December 5, 2002

9. Discuss new Inspection findings.

Response: No new degradation mechanisms were seen. Current active mechanisms for ONS-2:

a. Tube Support Plate Fretting Wear

b. Impingement

c. OD IGA in tubesheet crevice and freespan

d. PWSCC in upper tubesheet rolls and dents above 9 th TSP.

e. OD SCC in dents above 9th TSP and freespans above the 7 th TSP

f. Sleeve OD IGA/SCC in expansion transitions and parent tube adjacent to sleeve end Freespan indications have increased in number from previous inspections. The prediction of freespan cracking based on Weibul distribution indicates that a significant increase was expected. It's difficult to establish when the increase will begin to occur but this data indicates that significant increases would be expected in future inspections.

However, this is the last cycle of operation for these SGs prior to replacement. The number of freespan defects is within the worse case projections previously performed.

10. For1-600 plants discuss actions taken based on Seabrook'srecent findings.

Response: No additional actions have been identified for ONS units as a result of what is known of the Seabrook results to date. The ONS SG tubing is 1-600 HTMA and would not be expected to perform similar to the 1-600TT tubing at Seabrook.

11. Discussany use of Inspectionprobes other than bobbin and typical rotating probes.

Response: Probes used are typical designs. 0.510 mid-frequency bobbin, 0.460 Plus Point for RPC for tubes and 0.410 bobbin, 0.400 Plus-Point for sleeves.

12. Discuss In-situ pressuretest plans and results.

Response: Following is the number of tubes identified for in-situ testing. All testing followed EPRI guidelines for hold times. The maximum pressure was approx. 4300 psig, which represents 3 times normal AP plus adjustments for testing.

2A OTSG 2B OTSG Number Tested 10 (Axial) 11 Results No leakage Tube 37-27 leaked at 3900 psig

13. Describe tube pull plans andpreliminaryresults.

Response: No tube pulls were performed during EOC-1 9.

USNRC Document Control Desk Page 6 December 5, 2002 Attachment A The OTSG eddy current Inspection scope planned for the Oconee Unit 2 EOC-1 9 Refueling Outage:

Bobbin Coil (0.510 dia. MF) 100% A-OTSG 100% B-OTSG Lane and Wedge MRPC Two Rows Around Sleeved Tubes (0.460 dia. Plus Point) A and B OTSG MRPC Upper Tubesheet Roll 100% A-OTSG (0.460 dia. Plus Point) 100% B-OTSG MRPC Re-rolls Upper Tubesheet 100% A-OTSG (0.460 dia. Plus Point) 100% B-OTSG MRPC Lower Tubesheet Roll 100% Original Re-expansion (0.460 dia. Plus Point)

Bobbin Sleeve Exam 100% Sleeves A-OTSG (0.410 dia.) 100% Sleeves B-OTSG Sleeve Upper and Lower Rolls 100% Sleeve Rolls A-OTSG (0.400 dia Plus Point) 100% Sleeve Rolls B-OTSG Kidney Region (Sludge Pile) 100% A-OTSG (0.460 dia. Plus Point) 100% B-OTSG The inspection covers minimum 12 inches into the tubesheet RPC Special Interest (0.460 dia. Plus Point)

1) 100% Bobbin indications regardless of location

2) 100% of all dents regardless of size or location