ML20236S440

Summary of 861120 Meeting W/Util Re Proposed Tech Spec Changes to Snubber Surveillance Insp Intervals

ML20236S440
Person / Time
Site:	Farley
Issue date:	12/30/1986
From:	Reeves E Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
TAC-62811, TAC-62812, NUDOCS 8711250163
Download: ML20236S440 (18)

Text

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, I Docket Nos. 50-348 DISTRIBUTION and'50-364 Docket File % v Reeves (2) o NRC PDR D. M1iier ,

LICENSEE: Alabama Power Company (APCo) Local PDR- DELD ]

PAD #2 Rdg E. Jordan' FACILITY: Joseph M. Farley Nuclear Plant, J. Partlow B. Grimes:

Units 1 and 2 L. Rubenstein ACRS (10)

Gray File- NRC Participants

SUMMARY

OF MEETING HELD ON NOVEMBER 20, 1986, BETWEEN NRC AND AFCo REPRESENTATIVES TO DISCUSS APCo's PROPOSED TECHNICAL SPECIFICATION CHANGES TO SNUBBER SURVEILLANCE INSPECTION INTERVALS Introduction The NRC Project Manager (G. Requa, backup for E. Reeves) reviewed the purpose of the meeting which resulted from APCo's license amendment request proposed by letter dated September 2, 1986. The meeting was' held to assist the NRC staff's understanding of~APCo's proposal in order to meet the licensee's request amendment schedule of February 27, 1987. A' list of attendees is enclosed (Enclosure 1).

Discussion Southern Company Services (D.P. Hayes), representing Alabama Power Company (APCo), ,

used viewgraphs to present an overview of the proposed snubber visual inspection An outline of the discussion is enclosed as pages 1-4 of Enclosure methodolog(y.S.T.

2. APCo Burns) reviewed the refurbishment program of snubbers as follows:

1. All snubbers at Farley Unit No. I have been.. rebuilt.

2. All snubbers at Farley Unit No. 2 will be rebuilt by the end of the next outage.

3. The population of snubbers includes:

1

); Unit 1 Unit 2

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596 431 INACCESSIBLE 272 223 ACCESSIBLE l M 'E TOTAL Bechtel (E.W. Thomas) used viewgraphs (Enclosure 2, pages 5-14) to review the details of the statistical methodology. The approach is to maintain a 95 percent confidence level that 90 percent of the group remains operable based on visual inspections. Table 1 on page 14 of the Enclosure 2 reflects the proposed changes based on a snubber group size larger than 200. This table has been proposed by APCo in a letter dated September 2, 1986, for replacing Technical J Specification 4.7.9.a. visual inspection schedule which is based on a fixed number of inoperable snubbers per inspection period. APCo contends that the existing requirements are overly conservative and result in excessive surveillance requirements.

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8711250163 861230 i PDR ADOCK 05000348 P PDR l

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However, the staff indicated that the existing requirements are to maintain an approximately 95 percent confidence level that 90 to 100 percent of the snubbers are operable based on a combination of visual inspection and functional testing.

Conclusion Following discussions between the NRC staff and APCo's staff and their support organizations, APCo agreed to provide additional information at an early date to support the requested NRC staff action date of February 27, 1987.

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Edward Reeves, Project Manager Project Directorate #2 Division of PWR-A Licensing

Enclosures:

As stated e

Mr. R. P. Mcdonald Alabama Power Company Joseph M. Farley Nuclear Plant cc:

Mr.- W. O. Whitt D. Biard MacGuineas, Esquire Executive Vice President Volpe, Boskey and Lyons Alabama Power Company 918 16th Street, N.W.

Post Office Box 2641 Washington, DC 20006 Birmingham, Alabama ' 35291-0400 Charles R. Lowman Mr. Louis B. , Long, . General Manager Alabama Electric Corporation Southern Company Services, Inc.-

Post Office Box 550 Post Office Box 26P5 Andalusia, Alabama 364?0 Birmingham, Alabama 3520?

-Chairman. Regional Administrator, Region II Houston County Commission U.S. Nuclear Reaulatory Commission Dothan, Alabama 36301 101 Marietta Street, Suite 2000 Atlanta, Georgia 30303 Ernest L. Blake,' Jr.,- Esquire Shaw, Pittman, Potts and Trowbridge Claude Earl Fox, M.D. i 2300 N Street, N.W. State Health Officer Washington, DC 20037 State Department of Public Health State Office Building Montgomery, Alabama 36130 Robert A. Buettner,' Esquire Balch, Bingham, Baker, Hawthorne, Mr. J. D. Woodard

. Williams and Ward General Manager - Nuclear Plant

. Post Office Box 306 Post Office Box 470 Birmingham,. Alabama 35201 Ashford, Alabama 36312

. Resident. Inspector U.S. Nuclear Regulatory Commission Post Office Box 24 - Route 2 Columbia, Alabama 36319 l

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I ENCLOSURE 1 r.1 LIST OF ATTENDEES AT THE NOVEMBER 20, 1986 MEETING ROOM P-422 PHILLIPS BlflLDING BETHESDA, MARYLAND NAME ORGANIZATION G. Reoua PWR-A/ PAD #2 -

B. J. George Southern Company Services ,

D. P. Hayes Southern Company Services E. W. Thomas Bechtel Eastern Power Corporation S. Sue-Ung Bechtel Eastern Power Corporation K. Gandhi Bechtel Eastern Power Corporation

, K. Powers Southern Company Services S. T. Burns Alabama Power Company B. D. McKinney Alabama Power Company J. A. Ripple Alabama Power Company J. E. Garlington Alabama Power Company D. Terao NRC/NRR/DPLA/EB G. Johnson NRC/NRR/DPLA/EB S. Lee NRC/NRR/DPLA/EB H. Shaw NRC/NRR/ DBL /EB l H. L. Brammer NRC/NRR/PWP-A/EB T. Sullivan NRC/NRR/PWR-A/EB G. Bagchi NRC/NRR/PWR-A/EB d

ENCLOSURE 2 PROPOSED SNUBBER VISUAL INSPECTION INTERVAL TECHNICAL SPECIFICATION CHANGE PRESENTATION I. INTRODUCTION A. BACKGROUND B.

PROPOSEo SNUBBER TECHNICAL SPECIFICATIONS II. METHODOLOGY OVERVIEW III. COMPREHENSIVE METHODOLOGY REVIEW A. METHODOLOGY B. RESULTS IV.

SUMMARY

/ ACTION ITEMS A.

METHODOLOGY BASED ON SOUND STATISTICAL AND ENGINEERING PRINCIPLES B.

VISUAL INSPECTION INTERVALS 3ASED ON SAME CRITERIA AS FUNCTIONAL TESTING (95/90)

C. FOLLOW UP ACTION ITEMS 0825F G

o CHANGES TO VISUAL INSPECTION SCHEDULE 1

NO CHANGE TO 100% VISUAL INSPECTION REQUI"EMENT l

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NO CHANGE TO ACTION STATEMENT OR LCO o

NO CHANGE TO VISUAL TEST ACCEPTANCE CRITERIA o

NO CHANGE TO FUNCTIONAL TEST REQUI'EMENT o

NO CHANGE TO FUNCTIONAL TEST ACCEPTANCE CRITERIA o

NO CHANGE TO SERVICE LIFE MONITORING REQUIREMENTS 0825F S

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. STS METHODOLOGY  !

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DEVELOPED TO PROVIDE A 95% CONFIDENCE THAT AT LEA OF THE SNUBBERS ARE OPERABLE j o

BASED ON PROVIDING CONSTANT PROTE TION o

BASED ON TRADITIONAL STATISTICAL METHODS l

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e METHODOLOGY BASED ON SOUND STATISTICAL AND ENGIN PRINCIPLES o

VISUAL INSPECTION INTERVALS BASED ON SAME CRITERIA A FUNCTIONAL TESTING (95/90) o PROPOSED CHANGE IS SMALL PART OF C0t1PREHENSIVE SNU PROGRAM 0825F

METHODOLOGY FOR SNUBBER OPERABILITY SURVEILLANCE APPROACH:

• Maintain 95% confidence level that 90% of group remains operable

• Assume unlimited frequency of defined accidents may occur (l. e., probability of occurrence = 1)

• Use exponential distribution to predict time to failure of a given snubber

-its hazard function constant with time

• Number of failed snubbers before time (t) follows a binomial ,

distribution

• Estimate failure rate using chi-squared function (with a confidence level of 95%)

• Assume for all snubbers that fall, they do so at start of Inspection period

• Results of previous inspection interval used to establish new inspection Interval

• New inspection interval can be increased by only one interval step

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• Tolerances are provided on inspection Intervals. The extr. emes on tolerances that creates the most severe result is used in develop-ment of Inspection schedule.

G-WRW-11/86

DEVELOPMENT OF METHODOLOGY TIME TO FAILURE OF A GIVEN SNUBBER (X) FOLLOWS AN EXPONENTIAL DISTRIBUTION .

THEN PROBAEtLITY DENSITY FUNCTION CAN BE EXPRESSED AS :

-O* (I) x (X) = Oe WHERE O = FAILURE RATE PROBABILITY THAT AN INDIVIDUAL SNUBBER FAILS BEFORE TIME (t )

' -et (2)

Ps = P lI x < t ., = [. f x (fe ) d Ee = 1 - e i

IF Z IS THE NUMBER OF FAILED SNUBBERS BEFORE OR AT TIME (t ) , BY USE OF BINOMI AL DISTRIBUTION P(Z = z ) = zi(n_,33 Ps ( l - Ps )"~ * (3)

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WHERE n = TOTAL NUMBER IN GROUP S

PROBABILITY THAT THERE ARE NO MORE THAN (s)

SNUBBERS INOPERABLE BEFORE OR AT TIME (t )

P[z cs } =z=O $ zicj_,), P*,( l - P,)"~' (4)

USE P[z <s ]r = CONFIDENCE LEVEL = 95 %

COMBINING EQ'S 284 P{ z <s } =,o,$n!(n-z)! I l- *~ *I ('- t)"-2 =.95 (5)

EST6 MATE THE F ALLURE RATE $

_ Total number of failures (6)

O avg. Total test time an failed & unfalled units g_ - oG , 2 I+ 2 (6a) 2T WHERE = Chi- SQUARED FUNCTION T = ( n-1) T l = TOTAL NUMBER OF SNUBBERS WITH DEFECTS 1 T = CURRENT INSPECTION PERIOD oc = 0.05 CORRESPONDING TO 95% CONFIDENCE LEVEL CD

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JUSTIFICATION:

• 95% Confidence level of 90% Reliability

-Representative of criteria for safety systems l

- Produces very strict acceptance criteria

- Rigorous - less than 0.0076 failure rate to maintain same  :

Inspection interval l

• Unlimited frequency of accident events is a most conservative assumption

• Use of exponential distribution to predict time-to-fallure:

- Common ly used for simliar analysis of mechanical systems

-Inplace inspection and maintenance program leads to expectation that if snubber survives to a given time (t), -

its chance of survival the next instant is constant with time (Hazard Function)

- Exponential distribution ~ assumed in other approaches to 3 snubber inspection J

• Use of binomial probability function is appropriate for determining number of failures before time (t)

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- Failure of each snubber independent of others

- Represents a success-fallure event

- Mathematical exact

• Use of Chi-Squared Function

- For a exponential distribution, estimate of failure rate follows Chi-Squared distribution (mathematical exact)

- Conservatively uses a failure rate at 95% probability that l Its actual value will be lower G-WRW-11/86

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- j JUSTIFICATION CONTINUED

• Establishment of failure rate conservatively assumed all snubbers which fall do so at beginning of inspection interval

• Used latest information in establishing next interval

- Further restricted by allowing only one inspection interval step up from current interval

• Used most severe tolerance in estimate of failure rate and calculation of next inspection interval

- Use lower bound T to establish current failure rate

- Use upper bound T to establish % allowable Inoperative

• Minimum group size used to minimize next inspection j interval .

- rn /100 = I

• droup size limit tailored to Farley

• Methodology based on rigorous probabilistic and statistical procedures excerpted from standard texts i

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.g 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Fig. 314 . Hazard functions for normal, uniform, and exponential distributions.

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Durington and D.C. May,"Bandbook of Probability and Ekstistics," Handbook Publishers, Inc., fian-desity Ohio,1953.)

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RESULTS:

• Method is' valid for group of 200.or more

! - As group size increases, conservatism increases l

• Requires more frequent inspections with increasing failures

- Number of inoperative influenced by size of group

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• Applicable to each unit i

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TAB 1.E 1 g 3

Visu']s:1 inspection schedule for any group (cate ory) of snubbers

[ .. of the *loseph M. Farley Nuclear Power" Plant Un ts 3 and 2.

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'I y Cu vent Visual j Percerr. c) Saubrytrs Found Inoperabl6 'r, prr Current >

Next Visual Inspection Period

• Visus 1 Inspectit, Perir,d Inspection Period l

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24 Months.+** 25% r < 0.76% 24 Months + tsN f 0.76% >T r <x 0.99% 18 Months 7 25% D <

• <, 0.991. /< r 'l 1.40% ' 12 Honths T 25% A 1

i 1.40% < r 7 i .43%2 - 69tonths 7 25%

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" r > 2,471' 3 Months 7 25%.

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18 Months + 25% ' %. i r < 0.62% 24,#cnths + 25%

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O.62% T r < 0.76% :16 Months 7 25%

l' # T 1.09%.

p Cs.75%; 12 Months 7 25%

l N , 1.09% <r f. r (i 1.96% '

6 Months 7 25%

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3 Months [25%

~12 Kenths ~~

25 % r < c.585- 18 Months + 25%

6.68% T r < U.76% 12 Months 7 25%

0.76% <ri 1.80% 6 Monthe 7 25%

r > 1.4T% 3 Months [25%

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6 Months +~ 25% r=0 12 Months + 25%

0<r < 0.76% 6 Months 7 25%

r > 0.7T% 3 Months [ 25%

3 Months +~~ 25% r=0 6 Months + 25%

• r>0 3 Months [ 25%

Notes:

1. The above table is generated based on 95% confidence that at least 90% of the snubbers (in a group) being operable all the time.

2.

• Ear 21er visual inspection periods than required may be utilized. If this option is chosen, the criteria for determining the next visual inspection period shall be the criteria associated with the earlier visual insepetion period selected.

3. The above table is not. applicable for the snubber group' size (n) smaller than 200 .