ML18011A943

Forwards Plant Response to GL 95-03, Circumferential Cracking of SG Tubes.

ML18011A943
Person / Time
Site:	Harris
Issue date:	06/27/1995
From:	Robinson W CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-03, GL-95-3, HNP-95-059, HNP-95-59, HO-950566, NUDOCS 9507050064
Download: ML18011A943 (16)

Text

PRXOR1TY 1 (ACCELERATED RIDS PROCESSING)

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION, NBR:9507050064 DOC.DATE: 95/06/27 NOTARIZED: YES DOCKET g FACIL:50-400 Shearon Harris Nuclear Power Plant, Unit 1, Carolina 05000400 p AUTH. NAME AUTHOR AFFILIATION ROBINSON,W.R. Carolina Power S Light Co.

RECIP.NAME 'ECIPIENT AFFILIATION R Document Control Branch (Document Control Desk)

SUBJECT:

Forwards plant response to GL 95-03, "Circumferential Cracking of SG Tubes;"

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TITLE: OR Submittal: General Distribution R NOTES:Application for permit renewal filed. 05000400 I

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Carolina Power & Light Company William R. Robinson PO Box 165 Vice President New Hill NC 27562 Harris Nuclear Plant JUN 2'7 1995 File Number: HO-950566 SERIAL: HNP-95-059 United States Nuclear Regulatory Commission ATTENTION: Document Control Desk Washington, DC 20555 SHEARON HARRIS NUCLEAR POWER PLANT DOCKET NO. 50-400/LICENSE NO. NPF-63 GENERIC LETTER 95-03, CIRCUMFERENTIAL CRACKING OF STEAM GENERATOR TUBES Gentlemen:

In accordance with the provisions of NRC Generic Letter 95-03, "Circumferential Cracking of Steam Generator Tubes," dated April 28, 1995, Carolina Power 6g Light Company (CP6L) submits the response for the Shearon Harris Nuclear Power Plant.

Questions regarding this matter may be referred to Mr. R. W. Prunty at (919) 362-2030.

Sincerely, W. R. Robinson SDC/sdc Attachment W. R. Robinson, having been first duly sworn, did depose and say that the information contained herein is true and correct to the best of his information, knowledge and belief; and the sources of his information are officers, employees, contractors, and agents of Carolina Power 6 Light Company.

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0 Attachment to HNP-95-059 REQUIRED RESPONSE TO GENERIC LETTE<R 95-03, "CIRCUMFE<RENTIAL CRACKING OF STE<AM GENERATOR TUBES" The NRC issued Generic Letter (GL) 95-03, "Circumferential Cracking of Steam Generator Tubes," dated April 28, 1995 to request addressees complete the following three actions:

Evaluate recent operating experience with respect to the detection and sizing of circumferential indications to determine the applicability to their plant.

(2) On the basis of the evaluation in Item (1) above, past inspection scope and results, susceptibility to circumferential cracking, threshold of detection, expected or inferred crack growth rates, and other relevant factors, develop a safety assessment justifying continued operation until the next scheduled steam generator tube inspections are performed.

(3) Develop plans for the next steam generator tube inspections as they pertain to the detection of circumferential cracking. The inspection plans should address, but not be limited to, scope (including sample expansion criteria, if applicable), methods, equipment, and criteria (including personnel training and qualification).

The GL also requested that addressees submit:

~ a safety assessment justifying continued operation that is based on the evaluations performed in accordance with Requested Actions (1) and (2) above

~ a summary of the inspection plans developed in accordance with Requested Action (3) above and a schedule for the next planned inspection."

Shearon Harris Nuclear Power Plant (SHNPP) is providing the requested information as follows.

Evaluation and Safe Assessment - NRC Re uested Actions 1 dt, 2 Desi n and 0 eration SHNPP entered commercial service in May 1987 and is currently operating in Cycle 6. The SHNPP steam generators are Westinghouse Model D4 Steam Generators (SGs). SHNPP SGs have 3/4 inch outside diameter, Inconel 600 Low Temperature Mill Annealed (LTMA) tubes that are hardroll expanded for the full depth of the tubesheet. Tube support plates (TSPs) are carbon steel with drilled holes. The secondary system is constructed of ferrous materials with the exception of the condenser, which is copper-nickel. No tube sleeves have been installed in the SHNPP steam generators and a total of 35 tubes have been removed from service, including 11 tubes removed from service prior to startup.

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Attachment to HNP-95-059 SHNPP has taken action to prevent or slow the growth of Inter-Granular Attack Stress Coriosion Cracking (IGA/SCC) type degradation:

Prior to service, the low row U-bends (rows 1 0 2) were heat treated, the roll transition area of the hot leg tubes were roto-peened, and during the third refueling outage, the cold leg tubes roll transition area was shot-peened.

The plant has operated on all-volatile chemistry since startup, implemented secondary boric acid treatment in December 1992 and ethanolamine use in January 1994. Also, the SHNPP secondary chemistry program is based on EPRI and Westinghouse recommendations.

High pressure tubesheet washing (sludge lancing) has been performed during each refueling outage. Sludge lancing, and the fact that SHNPP has not used phosphate chemistry, minimizes the potential of "hard pile sludge" contributing to either Top of Tubesheet (TTS) circumferential cracking or detection problems.

~ Full flow condensate polishing has been employed since startup to control sludge copper levels, since excessive copper deposits on the Outside Diameter (OD) of tubing can "mask" defects making Eddy Current Testing (ECT) detection more difficult.

Copper levels during the last operating cycle were on the order of 0.03% or less.

~ The plant operated with T,, at approximately 589'F for the first five operating cycles.

As a result of a T., reduction program, SHNPP has operated at approximately 581'F T,, since the beginning of Cycle 6.

Steam Generator Ins ections SHNPP has performed eddy Current testing of the SG tubes. The testing included bobbin inspections. In addition, the Rotating Pancake Coil (RPC) probe was used in Refueling Outage (RFO) Nos. 4 and 5 to examine tubing at the TTS and certain TSPs. The scope of eddy current testing is listed in the table below. No circumferential cracking has been detected during these inspections.

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Attachment to HNP-95-059 Inspection Bobbin Scope RPC Scope Pre-Service Inspection 100% of open tubes None RFO 1 -20% of open tubes None RFO 2 -20% of open tubes Disposition of bobbin indications Mid-cycle Outage &50 tubes None

'FO 3 100% of open tubes Disposition of bobbin indications RFO 4 -25% of open tubes Disposition of bobbin indications, and

>>500 hot leg tubes in 'C'G (examined at TTS plus multiple TSPs)

RFO 5 100% of open tubes Disposition of bobbin indications, and total of +00 hot leg TfS in 'A'nd 'B'Gs Unit was removed from service to repair primary to secondary leakage caused by loose parts.

Although bobbin coil ECT inspections are not effective in directly identifying circumferential tube cracking, CP&L's review of industry experience shows that circumferential cracking is often preceeded by precursor damage that is detectable by bobbin coil testing.

SHNPP has employed secondary analysis in the form of independent two-party review during refueling outages 4 and 5 examinations to minimize the potential for "missed calls."

In addition to the ECT described above, SHNPP has performed destructive tube testing of two SG tubes pulled during RFO 4. One tube included the hot-leg tubesheet region through the first two TSPs, while the second tube included only the hot-leg tubesheet region including the TTS. Analysis of the tube samples revealed incipient IGA with shallow penetrations, scattered pitting, and minor wastage. The deepest IGA penetrations were found to be -2.2%

through wall. This is considered to be below the threshold of ECT detection. This damage mechanism is expected to eventually progress in the SHNPP SGs to the point were detection will ultimately be possible with ECT. The tube pull was performed at approximately 4.3 effective full power years of service, which was during the period of time that SHNPP operated at its highest T~,. Although IGA type damage is expected to continue, SCC types of damage mechanisms are considered to be temperature dependent, and thus are expected to continue at a lower growth rate due to the reduction in T~, at the beginning of Cycle 6. No circumferential cracking was detected in either tube sample.

Industr Ex erience Other domestic and foreign pressurized water reactors with recirculating steam generators which have design characteristics similar to SHNPP have experienced circumferential cracking at I) top of tube sheet intersections and roll transition area, 2) row I and 2 U-Bends, or 3) at dented tube support plates.

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Attachment to HNP-95-059 The table below, supplied by the Westinghouse Owners Group (WOG), lists the domestic plants which are most similar to SHNPP SG design and their experience with circumferential cracking at the top of tubesheet. These plants have I600 LTMA tubing with full depth hardroll expanded tubes, with the exception of Comanche Peak 1, which has full depth hardroll plus WEXTEX expanded tubes. Based on the table, CP&L considers circumferential cracking at the top of tubesheet a potential damage mechanism for SHNPP Westinghouse Model D4 SGs. This type of degradation is expected to be first observed in the hot leg.

Full Depth Hardroll Expansion Plants Alloy 600 LTHA TubinS Plant/ Steam Generator Hodel Startup First Time Location Tube Pull and Results Circ.

Cracking, Beaver Valley Unit 2/ 51H 1987 None N/A N/A Braidwood Unit 1/ D4 1987 2/95 Roll Transition No Byron Unit 1/ D4 1985 9/94 Roll Transition Yes, circ. ODSCC'es, Catawba Unit 1/ D3 1985 3/91 Roll Transition circ. ODSCC Comanche Peak Unit 1/ D4 1990 None N/A N/A Parley Unit 2/ 51 1981 3/89 Roll Transition Yes, shallow circ.ODSCC plus axial SCC HcGuire Unit 1/ D2 1981 1/90 Roll Transition Yes, circ. plus axial ODSCC HcGuire Unit 2/ D3 1983 7/93 Roll Transition No Shearon Harris/ D4 1986 None N/A Yes, incipient IGA (no SCC)

South Texas Unit 1/ E2 1988 2/93 Roll Transition Yes, circ. plus axial Watts Bar Unit 1/ D3 late 1995 N/A N/A N/A

• Outside Diameter Stress Corrosion Cracking (ODSCC)

Additionally, due to experiences at other plants with row 1 and 2 U-bend circumferential cracking experience, and similar tube material as SHNPP (I600 LTMA), CP&L considers SHNPP may be susceptible to low row U-bend cracking as well.

Finally, due to the discovery of circumferential cracking at dented tube support plates, found at North Anna 1 &, 2 (I600 LTMA tubing material), CP&L considers SHNPP susceptible to this mechanism, as well.

Safet Assessment The GL requested that licensees provide an assessment justifying continued operation until the next scheduled steam generator tube inspections are performed. CP&L's conclusion that continued operation is acceptable is based on the following considerations:

1. SHNPP is scheduled to commence RFO 6 in September 1995. Therefore, the time of continued operation that this assessment covers is approximately two months. At that Page 4 of 6

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Attachment to HNP-95-059 tiirte, additional inspections will be performed that are specifically targeted at detecting potential circumferential cracking of SG tubes.

CPAL has taken many actions to enhance the service life of the SGs. Some of these actions, such as the tube heat treatment and roto-peening, were implemented before the commercial operation of the facility. All-volatile chemistry control, full flow condensate polishing, and sludge lancing have been performed since startup. Other actions implemented after startup include boric acid treatment of the secondary, ethanolamine use for secondary PH control, cold leg shot peening, and Treduction.

Taken together, these actions are likely to prevent or slow the growth of IGA/SCC type degradation.

SHNPP has performed bobbin coil testing in each RFO in accordance with or in excess of EPRI recommendations. During RFOs 4 and 5 RPC testing was performed at the TTS and TSPs which are areas susceptible to circumferential cracking. SHNPP has also pulled and analyzed two SG tubes during RFO 4. No circumferential tube cracks have been identified either through ECT or through destructive laboratory analysis. Furthermore, the results of the ECT inspections performed to date have not shown significant levels of corrosion induced damage. No tubes have been removed from service due to OD IGA/SCC. Review of the industry experience with circumferential cracking shows that the detection of TTS circumferential cracking, without some level of detection of some other form of Inside Diameter (ID) or OD IGA/SCC, is unusual. Without the precursor damage mechanisms active on a significant scale, circumferential cracking is not expected to be a significant active damage mechanism.

4 Westinghouse has performed numerous burst tests on pulled tubes and has indicated that significant circumferential extent and throughwall degradation is required to challenge the Regulatory Guide (RG) 1.121 limits'. The Westinghouse Owners Group memorandum OG-95-53 provides an example of a limiting crack/degradation combination that still meets the Regulatory Guide 1.121 tube structural strength requirements. The WOG states that, for 3/4 inch tubing, the end of cycle structural limit for a circumferential oriented degraded tube would be a single uniform throughwall crack of 240', with 50% deep outside diameter degradation existing over the remaining 120'ube arc. A tube with this level of degradation would have sufficient strength remaining to satisfy the RG 1.121 3~P burst recommendations.

Based upon inspections performed previously at SHNPP, it is expected that substantial margin exists to the extent of degradation that would challenge the limits of RG 1.121.

SHNPP routinely monitors for primary to secondary leakage, and at the present time, there is no leakage above minimum detectable levels. Although not conclusive evidence, the lack of primary to secondary leakage is considered a positive indicator that the SGs have not experienced significant degradation during this period that call into question our ability to safely operate until RFO 6.

Regulatory Guide 1.121, " Bases for Plugging Degraded PWR Steam Generator Tubes."

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Attachment to HNP-95-059 4

Based on the above, it is CP&L's conclusion that operation of the SHNPP SGs until the next scheduled inspection, planned for September 1995, is justified.

Ins ection Plans - NRC Rc ucstcd Action 3 As stated above, the next scheduled inspection for SHNPP SGs is during RFO 6, which is scheduled to begin in September 1995. The inspection scope will also comply with the EPRI recommendations for inspection scope (sample size and areas of concern) for Westinghouse Model D steam generators with SHNPP's low tube plugging rate and no identified circumferential cracking. The inspection scope for RFO 6 will include, at a minimum for each SG:

20% full length tube inspection, 20% hot leg TTS inspection with a probe qualified for circumferential detection capability, 20% row 1 and 2 U-Bend inspection with a probe qualified for circumferential detection capability, and 20% dented tube support plate (>5 volt) inspection with a probe qualified for circumferential detection capability.

The probes to be used in the above inspections for circumferential cracking will be qualified in accordance with Appendix H of the EPRI Steam Generator Guidelines.

CP8'cL will expand each portion of the RFO 6 inspection program in accordance with the EPRI SG Inspection Guidelines or the Technical Specifications, whichever is more conservative. In RFO 6, CPAL will continue the practice of utilizing SHNPP site-specific Analyst Guidelines. Circumferential cracking will be addressed in the Analyst Guidelines including the "Points to Consider in Circumferential Crack Detection and Length Sizing" document provided by EPRI. RFO 6 analysts will be "IIA"qualified, and at a minimum, 75% of the analysts will meet the qualifications for Qualified Data Analysts (QDA's) as specified in the EPRI Examination Guidelines. Additionally, resolution and lead analysts will be QDA's. SHNPP will use a site-specific performance demonstration that will include written and practical examination elements to ensure that the analysts are aware of .

information contained in the site-specific Analyst Guidelines. Independent two-party review of data will also be employed.

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