ML20212J894

Safety Evaluation Supporting Amend 188 to License DPR-72

ML20212J894
Person / Time
Site:	Crystal River
Issue date:	10/01/1999
From:	NRC (Affiliation Not Assigned)
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NUDOCS 9910060029
Download: ML20212J894 (9)

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~ UNITED STATES 4

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NUCLEAR REGULATORY COMMISSION j

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO 188 TO FACILITY OPERATING LICENSE NO. DPR-72

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ALTERNATE REPAI'R CRITERIA'FOR STEAM GENERATOR TUBING FLORIDA POWER CORPORATION CRYSTAL RIVER UNIT 3 -

DOCKET NO. 50-302

1.0 INTRODUCTION

By letter dated May 5,1999, as supplemented on May 21, May 28, August 20, and i

September 2,1999, Florida Power Corporation (FPC or licensee) submitted for staff review a request for an amendment to the Crystal River Unit 3 Improved Technical Specifications (ITS).

The licensee _ proposed to implement alternate repair criteria that would allow tubes having axial tube end crack (TEC) indications in the upper and lower tubesheet of the once-through steam generators (OTSG) to remain in service. The May 21, May 28, August 20, and September 2, 1999, supplements did not affect the original proposed no significant hazards consideration determination, or expand the scope of the request as noticed in the Federal Reaister.

(f,4 FR 29710 (June 2,1999)).

The technical basis for the attemate repair criteria is contained in the Babcock & Wilcox Owners

~ Group topical report, " Alternate Repair Criteria for Tube End Cracking in the Tube-to-Tubesheet Roll Joint of Once Through Steam Generators," BAW-2346P, Revision 0 (proprietary).

Framatome performed analysis and testing for the alternate repair criteria and prepared the topical report for the Owners Group.

2.0 DISCUSSION in recent years, licensees have detected eddy current indications in the steam generator tubes near the upper tube end in the OTSGs in Babcock and Wilcox nuclear plants. The indications were characterized as tube end anomalies instead of cracking at the time of discovery because they were located on the tube above the primary face of the upper tubesheet and were considered outside of the primary pressure boundary. In 1998 licensees found that some tube end anomalies had grown into the cladding region of the tubesheet. Therefore, the tube end anomalies are now considered to be inside the primary pressure boundary and they have been reclassified as TEC indications.

In the summer of 1997, the licensee detected tube end anomalies in the Crystal River OTSG.

By letters dated June 18 and 30,1998, the licensee requested a technical specification

~ amendment to leave the tubes affected by tube end anomalies (now considered TECs) in service until either Refueling Outage 11 or during an outage of sufficient duration if such an 9910060029 991001 PDR ADOCK 05000302 P

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j-outage occurs before Refueling Outage 11. On July 30,1998, the U.S. Nuclear Regulatory Commission (NRC) issued License Amendment Number 169 approving the FPC request.

Crystal River is scheduled to enter Refueling Outage 11 in October 1999. The current

- amendment is to implement an alternate repair criteria for tubes having TEC indications.

The steam generator tube inspection data from various Babcock & Wilcox nuclear units have shown that TEC indications are initiated on the inside surface of the tubes and are typically short and axial oriented. They are usually located in the rolled portion of the tube near the heat-affected zone created by the tube-to-tubesheet seal weld. The degradation mechanism is identified as primary water stress corrosion cracking which is caused by residual stresses from the rolling of the joints in the tubesheet and from the seal weld.

Topical report BAW-2346P, Revision 0, delineates the following requirements and limitations for 1

application of the proposed altemate repair criteria:

9 Under the alternate repair criteria, axially-oriented indications located adjacent to the cladding region of the tube-to-tubesheet rolled joint, or in the portion of the tube protruding from the cladding, will be allowed to remain in service without repair.

" Adjacent to the cladding" refers to the portion of the tube that was rolled into the i

tubesheet cladding, as opposed to the portion of the tube that was rolled into the carbon steel portion of the tubesheet.

9 The attemate repair criteria do not apply to tubes with circumferential, mixed mode, or volumetric indications.

9 The alternate repair criteria do not apply to tubes with any portion of an axial indication that extends into the carbon steel region of the tubesheet.

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- The alternate repair criteria will only apply to those tubesheets whose cladding thickness is less than 0.625 inch.

9 The combined total leakage from all primary-to-secondary sources, including TEC indications left in service, shall not exceed the main steam line break accident leakage limit (one gallon per minute for Crystal River) mint:s operational leakage (150 gallons per day per SG for Crystal River). For tubes with multiple indications, a separate leak rate for each indication must be used.

O A plant-specific analysis for detected tube end cracks will be performed to establish a plant-specific growth rate or to verify the applicability of the generic growth rate in BAW-2346P, Revision O.

S' The total number of detected TEC indications (as an input to the leak rate analysis) must i

be increased to account for the probability of detection. This increase is specified to assess the population of undetected flaws.

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- O Site-specific inspections of tube rolled joints are required to identify locations and orientation of TEC. Location shallinclude tube location within the bundle and crack location with respect to the clad-to-carbon steel interface.

3.0 EVALUATION I

1 The staff evaluated the structural and leakage integrity of the tubes with TEC indications, 1

inspection methods, operational assessments specified in the alternate repair criteria, and I

technical specification wording to determine the acceptability of the proposed alternate repair criteria.

1 Structural Intearity The ends of each straight tube in the OTSGs are hard rolled into the upper and lower tubesheets. The roll joint is about 1-inch long inside the tubesheet and the tube end protrudes about 0.2 inch beyond the primary face of the tubesheet. Of the 1-inch length of the rolljoint, j

the cladding region of the tubesheet spans about 5/16-inch of that length and the rest of that roll length is spanned by the carbon steel region of the tubesheet. The upper and lower tubesheets provide a radial restraint to the hard roll portion of tubing which precludes the possibility of tube burst at TEC locations. The tubesheet also limits the affected tubes from bending in the vicinity of the TEC indications. The potential failure mode, therefore, would only be associated with the tensile axial loads that may cause the tube to fail within the rolled joint. The structural integrity is, therefore, dependent on the axial load carrying capability of the rolled joint and/or seal welds.

The structural strength of the tube affected by TECs is maintained if the seal weld can be demonstrated to resist the axial tube loads without assistance from any frictional forces that may be available from the hard rolljoint. Framatome has used a finite element analysis to qualify the structural integrity of the original fabrication seal (fillet) weld and the flush weld used to repair tube end damage at Crystal River 3 and Oconee Unit 1. The analysis assumes that the hard roll joint does not carry any portion of the tube load. The analysis evaluated the welds using loads from normal operating transient conditions and accident conditions. The analysis considered all loading medic.niams including primary and secondary pressures, tube axial loads and weld dilations. The analysis showed that the original seal weld and the flush repair weld satisfy American Society of Mechanical Engineers Code Section Ill for Class I components. Based on the analysis performed by Framatome, the staff finds the structuralintegrity of the tubes with TEC indications to be acceptable.

Leakaae Intearity The leakage integrity of the tubes was demonstrated by leak testing. Framatome performed leak testing to determine leak rates for rolled joints with through-wall axial cracks of various lengths for both steady-state power and bounding accident transient conditions. Leak rates at steady-state power conditions were determined to be comparable with the allowable primary-to-secondary leakage limit. The leakage at accident conditions was determined to be less than the allowable leakage limit under accident conditions.

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4 Before leak testing, Framatome used a finite element model to analyze the structural behavior of the tubes to determine test parameters that would give the least tight test rolljoints, which in turn (would give maximum possible leak rates in the leakage test. The analyzed conditions included l.

heatup, normal operating conditions, main steam line break, and a small-break loss-of-coolant accident. Framatome found that maximizing tube thickness, yield strength of the test tube, and tubesheet bore diameter and minimizing the yield strength of the tested tubesheet, cladding

' thickness, and roll joint torque would give the worst-case leak rates in the leakage test.

f Framatome fabricated 15 mockups to perform leakage tests. Each mockup included the simulated tubesheet with actual tubes rolled into the mockup block to form roll joints. The ends of the test tubes were sealed with fillet welds.' Each test tube had a through-wall notch to represent a TEC Indication.. The mockups were subjected to dilation to simulate tubesheet bowing under OTSG operating conditions followed by axial load cycling to simulate the 40 years Lof plant operation.

Leakage for normal power operation and accident conditions was evaluated to determine the leakage integrity of tubes with TEC indications. Framatome established the leak rates based on radial position of the tube in the tubesheet, axial tube loading, and tubesheet hole dilation in i

order to compensate for the tubesheet bowingc The leak rates that are to be applied to TEC indications to calculate the total leakage were established based on the statistical analysis of

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leak rates obtained in the leak tests. In the ttatistical analysis, Framatome applied a 95/50 i

bound (95 percent confidence that 50 percent of the leak rates were greater than the limit) to the leak rates obtained in the leak tests. The leak rates in the tests were very small compared to the leakage limits of 150 gallons per day for normal operation and the limit under accident conditions of one gallon per minute. Since the leak rates obtained from the testing are well within technical specification and accident analysis limits, they are acceptable.

Insoection Methods The licensee stated that during all future inspections a motorized rotating pancake coil will be used to inspect all hard roll expansions at tube ends with previously identified TEC indications that are monitored in the OTSG inservice inspection surveillance procedure. The licensee inspected all hard roll joints at tube ends using a motorized rotating pancake coil in 1997. The objective of inspecting previously identified TEC indications is to monitor their growth from cycle to cycle. The growth is measured in terms of the distance between the tip of the TEC indication

- and the clad-to-carbon steel tubesheet interface. The depth of the indications will not be measured because the licensee assumes that any detected axial TEC indication is 100 percent

.through-wal..

In future tube inspections, using a rotating pancake coil, the licensee will inspect 20 percent of hard roll expansions that have no previously identified TEC indications. The licensee will perform additional inspection samples in accordance with existing technical specification requirements depending on the inspection results. The inspection of the hard roll expansions will be based on Electric Power Research Institute (EPRI) Steam Generator Examination Guidelines, Revision 5. The objective of this inspection is to identify additional tubes with new

. TEC indications. New TEC indications will be included in the surveillance list and will be N

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& inspected in subsequent inspections, assuming the TECs satisfy the proposed alternate repair criteria.

--The licensee will use existing qualified techniques for flaw detection and determining flaw orientation. An inspection technique has been developed and qualified to locate axial TEC

. Indications relative to the cladding-to-carbon steel interface. Framatome has qualified the

. inspection techn!que consistent with the intent and protocol of EPRI Steam Generator Examination Guidelines, Revision 5. In addition, the rotating pancake coil (e.g., plus point coil) has been qualified in accordance with Appendix H of the EPRI Steam. Generator Examination

.. Guidelines, Revision 5, for detecting axial primary water stress corrosion cracking. Based on operating experience, the staff finds that the licensee's proposed inspection methods and scope are acceptable.

L Ooerational Assessment L

The alternate repair criteria specify that at the.end of each inspection, the licensee will perform an operational assessment to ensure that the estimated leakage from projected TEC indications i

at the end of the next cycle will not exceed the leakage limit under accident conditions. To i

project the.TEC indications at the end of the next cycle, the licensee will apply a probability of detection to the detected TEC indications. The application of the probability of detection will i

l increase the total TEC indications to account for non-detected indications. The number of TECs is calculated by dividing the number of detected indications by the probability of detection and subtracting those tubes with TEC indications that have been plugged or repaired.

L To project the total tube leakage, a 95/50 bounding leak rate is applied to each TEC indication according to its radial position within the tubesheet. The leak rates from all TEC indications are l

summed to obtain the total leak rate which is combined with all other known sources of primary-to-secondary leakage. The total leakage is compared to the accident leakage limit. If the projected leakage exceeds the limit, the alternate criteria require the licensee to repair tubes with TEC indications until the leakage limit is satisfied.

'During its review the staff questioned the conservatism of Framatome's use of the 95/50 bounding estimate in calculating the leak rate for each TEC indication and in calcuieting a probability of detection that is derived based on a 90 percent confidence level. The Framatome

' approach differs from the Generic Letter (GL) 95-05 methodology for a total steam generator leak rate. Framatome applies a 95/50 estimate to each TEC indication and adds leakage from all TEC indications to obtain total leakage for a steam generator, whereas GL 95-05 uses Monte Carlo simulation to estimate the leakage for all TEC indications and selects the 95/95 upper bound for the total leakage. The staff requested that the licensee address the conservatism of its total leakage calculation re".t* n th e rwhedology in GL 95-05.

The l]censee stated that its leakage calculation methodology is conservative relative to the

' methodology in GL 95-05 because leakage tests were conducted conservatively, in that: (1) the

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testing parameters were used in the leakage tests to give the maximum leak rate, (2) the simulated flaws in the test are all 100 percent through-wall which is conservative compared to I

the actual TECs in the field, and (3) in the leakage calculations, all TEC indications are assumed J

. to be leaking which is more conservative than actual field conditions.

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q l Based on 'the.stcff's suggestion, the licensee performed a total leakage calculation to obtain a 95/95 estimate of total SG leak rate using the methodology in GL 95-05. The results showed

~ that the GL 95-05 methodology estimated a lower total leak rate for en OTSG than the total leak L

rate estimated by the methodology in the topical report. The staff position is that the methodology in GL 95-05 provides a realistic bounding approach to leakage calculation. Since

'the methodology in the topical report provides more conservative results than the GL 95-05 calculation, the staff finds it acceptable.

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The licensee will evaluate and monitor.the growth rate of TEC indications during each inspection L

.to confirm that growth of TEC indications is insignificant. The length of the indication in the cladding is not of concern as long as the identified TEC indication does not grow and extend into the carbon steel region of the tubesheet. Current inspection data indicate that the growth rate of TECs is insignificant.

The staff finds that leaving tubes with TEC indications in service does not significantly increase

the risk associated with steam generator tube failure because the upper and lower tubesheets

. provide sufficient restraint to' preclude tube burst under normal and postulated accident conditions ano, as set forth above, tube leakage will be limited in accordance with the

methodology specified in the topical report. Therefore, the staff finds the licensee's proposed J operational assessment acceptableJ l-Prooosed Chances to Imoroved Technical Specifications

~ ITS 5.6.2.10.2.f: The licensee proposed.to add the following requirements to this section:

" Tubes in-service with' axially oriented tube end cracks (TEC) are identified in the OTSG j

Inservice inspection Surveillance Procedute. The portion 'of the tube with the axial TEC must be inspected using the motorized rotating coil eddy current technique during each subsequent i

inspection'.- No credit is to be taken for this inspection for meeting the minimum sample size l

requirement for random sample inspection.

' Tubes identified with axial TEC that meet the attemate repair criteria will be added to the

" existing list of tubes in the OTSG Inservice inspection Surveillance Procedure. Tubes identified with TEC during the previous inspection which meet the criteria to remain in-service will not be included when calculating the inspection category of the OTSG.

"The inspection data for tubes with axially oriented TEC indications shall be compared to the previous inspection data to monitor the indications for growth.

" Tubes with axially oriented TEC may be left in-service using the method described in Topical Report BAW-2346P, Revision 0, provided the combined projected leakage from all primary-to-secondary, leakage, including axial TEC indications left in-service, does not exceed the Main Steam Line Break (MSLB) accident leakage limit of one gallon per minute, minus 150 gallons per day, per OTSG.

"If the plant is required to shut down due to primary-to-secondary leakage and the cause is determined to be degradation of the TEC portion of the tubes,100% of the tubes with TEC in j

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.-. that OTSG'shall be examined in the location of the TEC. If more than 1% of the examined tubes are defective tubes,100% of the tubes with TEC in the other OTSG shall be examined in the

. location of the TEC.

" Tubes with crack-like indications within the carbon steel portion of the tubesheet shall be -

' repaired or removed from service using the appropriate approved method. Tubes with

' circumferentially oriented TEC or vo!umetric indications within the inconel clad region of the tubesheet shall be' repaired or removed from service using the appropriate approved method.

" NOTE" fFor the inspection conducted in accordance with 5.6.2.10.2.f only tubes with' new TEC indications identified after the 1997 inspection will be included in the below percentage calculations."

The "below percentage calculations" refer to calculations for inspection categories C-1, C-2, or C-3.

ITS 5.6.2.10.3.b: The licensee proposed the following requirement in this section:

' If the C-3 inspection results classification is due to including new tubes with TEC indications

= that meet the criteria to remain in-service no reduction in inspection frequency is required."

- lTS 5.6.2.10.4.a.12: The licensee proposed the following definition in this section:

" Tube End Cracks (TEC) are those crack-like eddy current indications, circumferentially and/or axially oriented, that are within the Inconel clad region of the primary face of the upper and lower

.tubesheets, but do not extend into the carbon steel-to-Inconel clad interface."

zlTS 5.7.2.c: This section specifies the reporting requirements for results of steam generator

~ tube inspections ( The licensee proposed the following additional item to be included in the inspection report:

" Number of tubes and axially oriented TEC indications left in-service, the projected accident -

. leakage, and an assessment of growth for TEC indicabons."

l The staff finds that the proposed changes incorporate requirements into the ITS to support the alternative repair criteria, which the staff found acceptable on the basis of review of information

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submitted by the licensee, and therefore the above changes to the ITS are acceptable.

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4.0 STATE CONSULTATION

Based upon a letter dated March 8,1991, from Mary E. Clark of the State of Florida, Department

.of Health and Rehabilitative Services, to Deborah A. Miller, Licensing Assistant, U.S. NRC, the State of Florida does not desire notification of issuance'of license amendments.

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8-50 ENVIRONMENTAL CONSIDERATIONS The amendment changes requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding (64 FR 29710).

Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmentalimpact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

7.0 CONCLUSION

The licensee has demonstrated that the steam generator tubes having tube end cracking indications that are allowed to remain inservice based on the proposed alternate repair criteria will maintain adequate structural and leakage integrity. The staff concludes that the proposed changes to technical specifications to implement the alternate repair criteria for tube end cracking are acceptable and they may be incorporated into Crystal River Unit 3 Improved Technical Specifications. The staff concludes that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributor: J. Tsao, DE/EMCB/NRR Date: October 1, 1999 I

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Mr. John Paul Cowen CRYSTAL RIVER UNIT NO. 3 Flonda Power Corporation oc:

Mr. R. Alexander Glenn Chairman Corporate Counsel (MAC-BT15A)-

Board of County Commissioners Florida Power Corporation Citrus County i

P.O. Box 14042 110 North Apopka Avenue St. Petersburg, Florida 33733-4042 invemess, Florida 34450-4245 j

1 Mr. Charles G. Pardee, Director-

- Ms. Sherry L. Bemhoft, Director i

Nuclear Plant Operations (PA4A)-

Nuclear Regulatory Affairs (NA2H)

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Flonda Power Corporation Florida Power Corporation l

Crystal River Energy Complex Crystal River Energy Complex:

15760 W. Power Line Street 15760 W. Power Line Street Crystal River, Florida _34428-6708 mystal River, Florida 34428-6708 Mr. Michael A. Schoppman senior Resident inspector j

Framatome Tecnnologies Inc.

Crystal River Unit 3 1700 Reckville Pike, Suite 525 U.S. Nuclear Regulatory Commission L

Rockville, Maryland 20852 6745 N; Tallahassee Road l'

Crystal River, Florida 34428 Mr. William A. Passetti, Chief Department of Health Mr. Gregory H. Halnon Bureau of Radiation Control Director, Quality Programs (SA2C) l 2020 Capital Circle, SE, Bin #C21 Florida Power Corporation f

Tallahassee, Florida 32399-1741 Crystal River Energy Complex l

15760 W. Power Line Street Attomey General Crystal River, Florida 34428-6708 Department of Legal Affairs L

The Capitol ~

Tallahaseee, Florida 32304 1

Mr. Joe Myers, Director Division of Emergency Preparedness 1

Department of Community Affairs i

2740 Centerview Drive i

Tallahassee, Florida 32399-2100 j

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