ML20044G756

Application for Amend to License NPF-8,changing Ts,On Interim Basis,To Replace Percent Tube Wall Degradation Criteria Currently Employed W/More Appropriate Method for Determining Serviceability of Tubes W/Flaw Indications

ML20044G756
Person / Time
Site:	Farley
Issue date:	05/28/1993
From:	Woodard J SOUTHERN NUCLEAR OPERATING CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20044G757	List: ML20044G756 ML20044G758
References
NUDOCS 9306040210
Download: ML20044G756 (5)

Text

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Southern Nuclear Operating Company t , pes; (yfice se,1295 Bamingham. Alaba~a 35201

. Te!ephone 205 0035086 u

a. o. w w oara Southem Nuclear Operating Company Vscc Presdent the sou: hem electnc system Fade / Protect May 28, 1993 Docket No. 50-364 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Joseph M. Farley Nuclear Plant - Unit 2 Steam Generator Tube Support Plate Interim Pluqaina Criteria Gentlemen:

By letter dated February 26, 1991, Alabama Power Company submitted a steam generator tube support plate alternate plugging criteria. As a result in delays in approving the full voltage alternate plugging criteria, Southern Nuclear Operating Company (SNC) submitted a reduced voltage interim plugging criteria for both Unit I and Unit 2. The Unit 2 interim plugging criteria was approved on April 1,1992 and the Unit I criteria was approved on October 8,1992. As a result of further delays in approval of the full voltage alternate plugging criteria, SNC proposes the use of reduced voltage interim plugging criteria for Unit 2 for the next operating cycle. NRC approval is requested by August 27, 1993.

Southern Nuclear proposes that the Farley technical specifications be modified, on an interim basis, to replace the percent tube wall degradation criteria currently employed with a more appropriate method for determining serviceability of tubes with flaw indications at the tube support plate intersections. The appropriate method for determining serviceability is by a methodology that more reliably assesses structural integrity. As a result of the structural integrity assessment at Farley Nuclear Plant, tube indications within the tube support plate with a bobbin coil voltage less than or equal to 1.0 volt will be left in service. Southern Nuclear will continue to ensure that primary-to-secondary leakage as a result of a steam line break is sufficiently low to ensure the dose at the site boundary is a small fraction of the Part 100 limits. In addition, Southern Nuclear proposes to modify the Unit 2 technical specifications to reduce the total allowable primary-to-secondary operational leakage from any one steam generator from 500 gallons per day to 150 gallons per day. The total allowable primary-to-secondary operational leakage through all steam generators will be reduced from one gallon per minute (1,440 gallons per day) to 450 gallons per day.

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9306040210 930528 PDR ADOCK 05000364 (1 P ppy \

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i U. S. Nuclear Regulatory Commission Page 2 Since Southern Nuclear's last interim plugging criteria submittal, additional data have been provided to the NRC Staff in other alternate / interim plugging -

criteria submittals. These data points underscore the conservatism contained in a 1 volt interim plugging criteria for Farley Nuclear Plant. Furthermore, two tubes were pulled from Farley Unit I during its last outage. Although these two tubes had relatively high voltages, 3.3 and' 3.2 volts, they exhibited no leakage under steam line break differential pressures. In addition, these same two tubes burst at differential pressures of 6,600 psig and 8,100 psig respectively. These burst i:ressures are over twice the differential pressure expected in a steam line break.

Attachment I contains the proposed interim voltage plugging criteria including a sampling program. Attachment 2 contains the proposed changed Technical Specification pages_in support of the interim plugging criteria. Attachment 3 provides a significant hazards evaluation for the proposed interim plugging criteria in accordance with 10 CFR 50.92. Attachment 4 provides the proposed eddy current guidelines for use in the upcoming outages, assuming the interim criteria is approved for use. Attachment 5 contains the supporting environmental evaluation.

If there are any questions, please advise.

Respectfully submitted, SOUTHERN NUCLEAR OPERATING COMPANY b

Woodard M

JDW/ REM:cht-IPCREV5 NEL-93-0193 SWORN TO AND SUBSCRIBED BEFORE ME Attachments THISc7[A DAY OF N% 1993 cc: Mr. S. D. Ebneter Mr. T. A. Reed A. M. ' - _

Mr. G. F. Maxwell / fy'6t j4'/PubTTc Dr. D. E. Williamson / v My Commission Expires: 9-/Y-f'V  !

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i Attachment'l Voltage Plugging Criteria- L

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Interim Plugging Criteria i

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. j Southern Nuclear Operatina Company proposal:

Voltage Plugging Criteria

1. A bobbin inspection of 100% of the hot and cold leg steam generator tube i support plate intersections will be performed. Intersections which are ~

inaccessible due to sleeving or the U-bend may be inspected with a reduced size probe, as outlined in WCAP-13692, Responses to NRC Questions on NRC Analytical Model for SLB Leakage of ODSCC at TSPs (previously submitted by ,

Westinghouse by letter dated April 14,1993).  ;

2. Flaws within the bounds of the tube support plate with bobbin voltage less than or equal to 1.0 volt will be allowed to remain in service. j

3. Flaws within the bounds of the tube support plate with a bobbin voltage. -

greater than 1.0 volt will be repaired or plugged except as noted in 4.

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4. Flaw indications within the bounds of the tube support plate with a bobbin voltage greater than 1.0 volt but less than or equal to 3.6 volts may remain in service if a rotating pancake coil probe (RPC) inspection does i not detect a flaw. Flaw indications with a bobbin voltage greater than i 3.6 volts will be plugged or repaired. j l

S. A sample RPC inspection of a minimum of 100 tube support plate i intersections will be performed. All intersections with a bobbin dent  !

voltage exceeding 5 volts will be inspected. Other intersections in the '

sample population will be based on inspecting intersections with artifact indications and intersections with unusual phase angles. Expansion of the sample plan, if required, will be based on the nature and number of the flaws discovered.

6. RPC flaw indications not found by the bobbin due to masking effects (due to denting , artifact indications, noise) will be plugged or repaired.

End-of-Cycle (E0C) Voltage Distribution j i

Acceptable methods for determining the E0C voltage distribution are as follows:

1. The methodology described in WCAP-12871, Revision 2. (This involves l sampling the cumulative probability distribution of NDE uncertainty and  !

the voltage growth rate using Monte Carlo techniques and applying the results to the beginning-of-cycle (B0C) voltage distribution.)

2. A simplified approach may be used as an alternative (to the WCAP-12871, )

Revision 2 approach) provided it provides for a conservative treatment of the tails of the cumulative probability distributions of NDE uncertainty and the voltage growth rate to the 100% cumulative probability values.

Steam Line Break Leakage Steam line break leakage as a function of E0C voltage (E0C-V) shall be determined as follows: '

E0C Voltaae SLB Leakaae  !

E0C-V s 2.5 volts 0 liter / hour 8 2.5 volts < EOC-V s 4 volts 1 liter / hour EOC-V > 4 volts 10 liters / hour  ;

Should the calculated steam line break leakage exceed the 1 gallon per minute Farley technical specification limit, tubes with the highest voltages would be  :

plugged or repaired until the 1 gallon per minute leakage rate is satisfied. '

Safety Analysis WCAP-12871, Revision 2, J.M. Farley Units 1 and 2 SG Tube Plugging Criteria for ODSCC at Tube Support Plates, provides the development of a 3.6 volt alternate plugging criteria. Use of a 1.0 volt threshold for app:ication of the current Technical Specification is more conservative than the use of the 3.6 volt criteria. Burst pressure for steam generator tubes with flaws within the bounds of the tube support plate will still meet the requirements of Regulatory Guide 1.121.

The Farley interim plugging criteria proposes that tubes within the bounds of the tube support plate with flaw indications with bobbin voltage less than or equal to 1.0 volt be allowed to remain in service. Steam line break leakage ;

must take into account the expected leakage from these flaws. This will be accomplished by using the thresholds in the steam line break leakage as a i function of E0C voltage table above. Use of these limits for leaving tubes in service will ensure that leakage in the event of a steam line break will remain less than the 1 gallon per minute limit currently in the bases of the Farley  :

technical specifications. l l

The steam line break leakage values of 0,1,10 liters / hour for the voltage  !

range shown on the steam line break leakage as a function of E0C voltage table l are considered to be conservative based on WCAP-13464, " Response to NRC  !

Questions on Farley SG Tube Alternate Plugging Criteria Presentation Material." l l

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