ML20079C043

Rev to Tech Spec 4.7.7, Snubbers Surveillance Requirements Re Fastners for Attachment of Snubbers to Components & Anchorages

ML20079C043
Person / Time
Site:	Summer
Issue date:	06/11/1991
From:	SOUTH CAROLINA ELECTRIC & GAS CO.
To:
Shared Package
ML20079C041	List: ML20079C040 ML20079C043
References
NUDOCS 9106180320
Download: ML20079C043 (11)

Text

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PLANT SYSTEMS 3/4.7.7 SNUBBERS LIMITING CONDITION FOR OPERATION 3.7.7 All snubbers on systems required for safe shutdown / accident mitigation This includes safety and non-safety related snubbers on shall be OPERABLE.

systems used to protect the code boundary and to ensure the structural integ-rity of these systems under dynamic loads.

APPLICABILITY: MODES 1, 2, 3 and 4. MODES S and 6 for snubbers located on "

systems required OPERABLE in those MODES.

ACTION:

With one or more snubbers inoperable, within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> replace or restore the inoperable snubber (s) to OPERABLE status and perform an engineering evaluation per Specification 4.7.7.g on the attached component or declare the attached system inoperable and follow the appropriate ACTION statement for that system.

SURVEILLANCE REQUIREMENTS 4.7.7 Each snubber shall be demonstrated OPERABLE by performance of the following augmented inservice inspection program and the requirements of Specification 4.0.5.

a. Inspection Types As used in this specification, type of snubber shall mean snubbers of the same design and manufacturer, irrespective of capacity.

/ b. Visual Inspections _ ,

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'The first inservice visual inspection of oach type of snub cing POWER p formed aftec 4 months but within 10 months of c ection 3.7.7.

h e OPERA and shall include all snubbers defined 'anoperable during two snubbers of each type are foi l

If less t end inservice visual l J

the first ins ice visual inspection, the 5% from the date of the inspection shall performed 12 monthst visual inspections shall be l

first inspection. ervise, subse lowing schedule:

performed in accordanc with th No. Inoperable Snubbe f each Subsequent Visual , (

er. Inspection Period *_

type par Inspectio 0

18 months 1 25%

1 12 months i 25%

6 months 1 25%

g 124 days t 25%

3,4 62 days t 25%

r>

5,6,7 days i 25%

$$ 8 cr more 380- be lengthened

• The inspe on inte "al for each type of snubber shall n identified 38 M more th one step at a time unless a generic problem has b ened one ox and rected; in that event the inspection interval may be len of the first time and two steos thereafter if no inoperable snubb

$8 st at type are found.

provisions of Specification 4.0.2 are not applicable,

= --

p g, 3/4 7-16 Amendment No. 41 SU!HER - UNIT 1 4PD MISERr 4.7' 76 ___

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1 l PLANT SYSTEMS SURVEILLANCE REQUIREMENTS (Continued)

c. Refuelino Outage Inspections EuAN/ue/ggap3 l ^t M :;; c.;; p.,

L^ ;;r,th:3an inspection shall be performed of all the snubbers defined in Section 3.7.7 attached to sections of safety l systems piping that have experienced unexpected, potentially damaging I transients as determined from a review of operational data and a l visual inspection of the systems. In addition to satisfying the visual inspection acceptance criteria, freedc.. of motion of mechanical snubbers shall be verified using at least one of the following: (1) manually induced snubber movement; (ii) evaluation of in place snubber piston setting; or (iii no the mechanira snubber through its full range of trave att c74 mal d C [dAGrWJ[#

. Visual Inspection Acceptance Criteria jw,,guYfg f #

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h) i Visual ir.spections shall verify (1) that thero re no visibl~

indications of damage or impaired OPERABILITY and (2) attachments to the foundation or supporting structure erey :: r c r _S_nubbers which

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/.h_ -E96MG44 for the appear inoperable as a result of visual inspections % """"

Jnterval. orovided thatJ4) the causeEcf th; r;j;ctirr is clearly

{ festablished and remedied for that par Icular snubber and for other Ih f>

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snubbers irrespective of type that may be generically susceptible; 4g N@$ and ) the affected snubber is functionally tested in the as found i A g ondition and determined OPERABLE per Specifications 4.7.7.f.

a fluid port of a hydraulic snubber is found to be uncovered the When I snubber shall be declared inoperable and shall not be determined f 1 OPERABLE via functional testing unless the test is started with the l &

piston in the as found setting, extending the piston rod in the tension mode direction. All snubbers' connected to an inoperable l common hydraulic fluid reservoir shall be counted as @ :- M M .  !

' ~ ~ '

i l e. Functional Tests 7 (Wf li1Sc1t4.7.7d. ,

During the first refueling shutdown and at least once per 18 months thereaf ter during shutdown, a representative sample of either:

i (1) At least 10% of the total of each type of snubber in use in the plant shall be functionally tested either in place or in a bench test. For each snubber of a type that does not meet the functional test acceptance criteria of Specification 4.7.7.f an additional 10% of that type of snubber shall be functionally tested until no more failures are found or until all snubbers of that type have been functionally tested, or (2) A representative sample of each l-typ~e of snubber shall be functionally tested in accordance with Figure 4.7-1, "C" is the total number of snubbers of a type found not meeting the acceptance requirements of Specification 4.7.7.f.

The cumulative number of snubbers of a type tested is denoted by "N." At the end of each day's testing, the new salues of "N" and "C" (previous day's total plus current day's increments) shall be 1 plotted on Figure 4.7-1. :f -et ;.., th: th; p;i , pied '9't in th. "^w 3d" , ;;;i;r ; ;mbs. . m' that b e , o o ',1 L v

'r rti: all., m tid. If at any time the point plotted falls in SUMMER - UNIT 1 3/4 7-17 Amendment No. 41

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PLANT SYSTEMS SURVEILLANCE REQUIREMENTS (Continued)

e. Functional Tests _ (Continued) the " Accept" region testing of that type of snubber may be terminated. When the point plotted lies in the " Continue Testing" region, additional snubbers of that type *" shall be tested until the or all point f alls in the " Accept" region ""P'" - ;'

the snubbers of that type have been tested.

The representative sample selected for functional testing shall include the various configurations, operating environments, and the range of size and capacity of snubbers of each type. The represen-tative sample shall be weighted to include more snubbers from severe service areas such as near heavy equipment. Snubbers placed in the same location as snubbers which failed the previous functional test shall be included in the next test lot if the failure analysis shows that failure was due to location, f.

Functional Test Acceptance Criteria Tha snubber functional test shali verify that:

1. Activation (restraining action) is achieved within the specified range in both tension and compression, except that inertia dependent, acceleration limiting mechanical snubbers, may be tested to verify only that activation takes place in both =

directions of travel.

2. Snubber bleed, or release rate where required, is present in both tension and compression, within the specified range.

3. Where required, the force required to initiate or maintain motion of the snubber is within the specified range in both direction of travel.

4. For snubbers specifically required not to displace under continuous load, the ability of the snubber to withstand load without displacement.

5. Fasteners for attachment of the snubber to the component and to the snubber anchorage are secure.

Testing methods may be used to measure parameters indirectly or parameters other than those specified if those results can be correlated to the specified parameters through established methods.

g. Functional Test Failure Analysis An' engineering evaluation shall be made of each failure to meet the functional test acceptance criteria to determine the cause of the failure. The results of this evaluation shall be used, if applicable, in selecting snubbers to be tested in an ef fort to determine the OPERABILITY of other snubbers irrespective of type which may be subject to the same failure mode.

SU M ER - UNIT 1 3/4 7-18

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ACCEPT 1 r 0 10 20 30 40 to to 70 to 90 100 I N

I am FIGURE 4.7-1 SAMPLING PLAN FOR SUNBBER FUNCTIONAL TEST SUl+1ER - UNIT 1 3/4 7-20 l

_ABlE T 4.7-2 SNUBBER VISUAL INSPECTION INTERVAL NUMBER OF UNACCEPTABLE SNUBBERS Population Column A Column B Column C or Category Extend Interval Repeat Interval Reduce Interval (Notes 1 and 2) (Notes 3 and 6) (Notes 4 and 6) (Notes 5 and 6) 1 0 0 1 0 2 s 0 0 1 4 100 150 0 3 8 200 2 5 13 300 5 12 25 400 8 18 36 12 24 48 o 500 750 20 40 78 29 56 109 1000 or greater TABLE NOTATION l

l (1) The next visual inspection interval for a snubber population or category size shall be determined based upon the previous inspection interval and the number of unacceptable snubbers found during that internal. Snubbers i may be categorized, based upon their accessibility during power operation,

! as accessible or inaccessible. These categories may be examined I separately or jointly. However, the licensee must make and document that decision before any inspection and shall use that decision as the basis upon which to datermine the next inspection interval for that category.

(2) Interpolation between population or category sizes and the number of unacceptable snubbers is permissible. Use next lower integer for the value l of the limit for Columns A, B, or C if that includes a fractional value of unacceptable snubbers as determined by interpolation.

(3) If the number of unacceptable snubbers is equal to or less than the number in Column A, the next inspection interval may be twice the previous interval but not greater than 48 months.

(4) If the number of unacceptable snubbers is equal to or less than the number in Column B but greater than the number in Column A, the next inspection interval shall be the same as the previous interval.

SumER - UNIT 1 3/4 7-21

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SNUBBERS TABLE 4.7-2 (CONTINUEU)

TABLE NOTATION (5) If the number of unacceptable snubbers is e" pal to or greater than the number in Column C - the next inspection int- al shall be two-thirds of the

!- previous interval. However, if the number or unacceptable snubbers is less than the number in Column C-but greater than the number in Column B. the

^

next interval shall be reduced proportionally by interpolation, that is, I l the previous interval shall be reduced by a factor that is one-third of the L ratio of the difference between the number of unacceptable snubbers found L during the previous' interval and the number in Column B to r- difference i L in the numbers in Columns B and C.

! q (6) The provi31ans of Specifi:ation 4.0.2 are applicable for all inspection i intervals up to and including 48 months, i l

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SUMMER - UNIT l' 3/4 7-22 L

PLANT SYSTEMS BASES . .

ULTIMATE HEAT SINA (Continued)

The limitations on minimum water level and maximum temperatur., are based on providing a 30 day cooling water supply to safety related equipment without exceeding their design basis tempercture and is consistent with the recommendations of Regulatory Guide 1.27, " Ultimate Heat Sinn for Nuclear ~

Plants", March 197a.

3/4.7.6 CONTROL ROOM NORMAL AND EMERGENCY AIR HANDLING SYSTEM Tne OPERABILITY of the control room ventilation system ensures that

1) the ambient air temperature does not exceed the allowable temperature for continuous duty rating for the equipment and instrumentation cooled by this system and 2) the control room will remain habitable for operations personnel The OPERABILITY of during and following all credible accident conditiens.

this system in conjunction with control room design provisions is based on limiting the radiation exposure to personnel occupying the control room to 5 rem or less whole body, or its equivalent. This limitation is consistent "A", 10 CFR 50.

with the requirements of General Design Criteria 19 of Appendix 3/4.7.7 SNUBBERS .

All snubbers on systems required for safe shutdown / accident mitigation shall be OPERABLE.

This includes safety and non-safety related snubbers on systems used to protect the code boundary and to ensure the structural integrity of these systems under dynamic loads.

Snubbers are classified and grouro by design and manufacturer but not by uti'iizing the same design features of size. For example, mechanical snubbe-the 2 kip,10 kip and 100 kip capacity manufactured by company "A" are of the for same type. The same design mechanical snubber manufactured by company "B" the purposes of this specification would be of a different type, as would hydraulic snubbers from either manufacturer. .

The visual inspection frequency is tased upon maintaining a constant level of snubber protection to systems. TMrefore, the required inspection interval varies inversely with the observed snubber failures and h determined '

by the number of inoperable snubbers found Juring an inspection.fInspecticns performed before that interval has elapsed may be used as a new reference A =uar, +ha ra s9 t e e' Such eerh point to determine the next inspection.

4Mpectf 0ns peefc nd befon th: Origin;? r:pired-ti : '-terv:1 required5:: chp:Od inspect 4*

( eminel time 1c55 25%) may-not-be used to 1:ngthen th:

- int:rv:h Any inspection whose results require a horter inspection interval will override the previous schedule. m- -- --

Table 4:]t.2 e.faber/vs 71rritt livro&prc4hnrir!% YA' *!"'d R, V

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B 3/4 7-4 Amendment No. 41 SUMMER - UNIT 1

PLANT SYS1 EMS BASES SNUBBERS (Continued) i

' l To provide assurance of snubber functional reliability one of two sampling )

and acceptance criteria methods are oced:

l

1) functionally test 10 percent of a type of snubber with an additi.onal 10 percent tested for each functional testing failure, or

2) functionally test a sample size and determine sample acceptance oe--. i l

---ec j c ; t i .m using Figure 4.7-1.

l Figure 4.7-1 was developed using "Wald's Sequential Probability Ratio Plan" as described in "Quility Control and Industrial Statistics" by Acheson J. Duncan.

i The service life of a snubber is established via manufacturer input and information through consideration of the snubber service conditions and l

l associated-installation and maintenance reccrds (newly installed snubber, seal replaced, spring replaced, in high radiation area, in high temperature. area, etc. . .). The requirement to monitor the snubber service life is included to s ensure that the snubsers periodically undergo a performance evaluation in view of their age and operating conditions. These records will provide statistical bases for future consideration of snubber service life. The requirements for theaffect

-to maintenance of records and the snubber service life review are not intended plant operation.

Permanent or other exemptions from the surveillance program for individual snubbers may be granted by the Commission if a justifiable basis for exemption is presented and, if applicable, snubber life destructive testing was performed to qualify the snubber for the applicable design conditions at either the completion of their fabrication or a; a subsequent date. Snubbers so exempted shall be listed in Section 3.7.7 with footnotes indicating-the extent of the exemptions.

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i SUMMER - UNIT 1 B 3/4 7-5 Amendment No.;;

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Enclosure 2 to Document Control Desk Letter TSP 910003-1 Paga,1 of 1 I

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. PROPOSED TECHNICAL SPECIFICATION CHANGE - TSP 910003-1 VIRGIL C. SUMMER NUCLEAR STATION DESCRIPTION AND SAFETY EVALUATION DESCRIPTION OF CHANGE-l SCE&G proposes to modify the Virgil C. Summer Nuclear Station Technical Specifications (TS) to revise TS 4.7.7 and associated Bases 3/4.7.? in i accordance with GL 90-09; additionally, the REJECT line in figure 4.7-1 and all references to this line are deleted from the text. The proposed amendment changes the snubber visual inspection schedule of surveillance l_ requirement '.7,7 to the alternate visual inspection schedule specified by

'- GL 90-09, and changes the' associated Bases 3/4.7.7.

SAFETY EVALUATION Snubbers are designed to prevent unrestrair,ed motion of piping systems and components under dynamic loading, while allowing normal thermal expansion and contractions to occur.during plant startup, operation, and shutdown. The proposed changes do not involve any change to the plant configuration or its mode of operation as described in the safety analysis report. Existing safety analyses and safety assumptions are not affected nor need to be changed. All snubbers and related components will continue to be visually and functionally inspected; therefore, the:r operability will not be affected. Deletion of the Reject line from figure 4.7-1 and its references in the text are needed to reflect actual testing strategy. The use of the

Reject.line is incorrect since this line assumes a totally homogeneous sample and that.the failures of the total population are in the same ratio as the failures in the selected sample.

i

Enclosure.3 to Document Control Desk Letter

.' TSP 910003-1 Page,1 of 2 PROPOSED TECHNICAL. SfliFICAT'ON CHANGE - TSP 910003-1 VIRGIL C. SUMER NUCLEAR STATION DETERMINATION OF N0 SIGNIFICANT HAZARDS CONSIDERATION DESCRIPTION OF CHANGE SCE&G proposes to modify the Virgil C. Summer Nuclear Station Technical Specifications (TS) to revise TS 4.7.7 and t sociated Bases 3/4.7.7 in accordance with GL 90-09; additionally, the 'ECT line in figure 4.7-1 and all references to this line are deleted fr text. The proposed amendment changes the snubber visJal inspec, .n schedule of surveillance requirement 4.7.7 to the alternate visual inspection schedule specified by GL 90-09, and changes the associated Bases 3/4.7.7.

SIGNIFICANT HAZARDS EVALUATION SCE&G has evaluated the proposed technical specification change and has )

determined that it does not represent a significant hazard consideration '

based on the criteria established in 10 CFR 50.92. Operation of Virgil C. '

Summer Nuclear Station in accordance with the proposed amendment will not:

(1) involve a significant increase in the probability or consequences of an accident previously evaluated.

The proposed change will allow extension of subsequent visual survei_llance intervals based on the number of unacceptable snubbers found during the previous inspection, in accordance with the guidance contained in GL 90-09. This change will not involve any change to the actual surveillance requirements, lnere will be no increase in the probability of failure of components ard systems that would result from extending the visual surveillance interval. Reliability is ensured by functional-testing which provides a 95 percent confidence level that 90 to 100 percent of the snubbers will operate within their specified acceptance limit.

The Rejec. line, developed using Wald's Sequential Probability Ratio Plan, astumes that the sample is totally homogeneous, and that the failure in the total population is in the same ratio as the failures observed in a given sample. This is not correct when functionally testing snubbers in nuclear power stations. Snubbers can not be considered a homogeneous population, since the sampling for functional testing includes various configurations, different environmental conditions, different sizes, capacities and typas of snubbers, and the sample is weighted to include more snubbers from severe service areas.

_ ._.__._. _ _ _ _ ____ _ _ _ _T

Enclosure 3 to Document Control. Desk Letter c TSP 910003-1

. Page 2 of 2 4'

(2)- create the possibility of a-new or different kind of accident from any previously analyzed.

The proposed change will not make physical alterations to any plant system, structure or component, will not change the method by which a safety-related system performs its function, and will not change the way the surveillance requirement is performed. The proposed change will only allow extensica of a subsequent snubber visual inspection if the number of unacceptab e snubbers found during a given inspection is i

equal or less than the number of unacceptable snubbers given in the new SNUBBER VISUAL INSPECTION-It1TERVAL table. Deletion c' tha Reject line from figure 4.7-1 does not contribute to any new or E ffeient kind of accident.

(3) involve _a significant reduction in a margin of safety.

The-proposed change will not alter existing surveillance requirements; therefore, the reliability, ensured through functional testing, will not be degraded. Visual examinations complement the functional testing .

of snubbers and provide additional confidence of snubber reliability.  !

VCSNS operating experience indicates that existing maintenance programs are effective in mir.imizing snubber failures, as demonstrated by the low snubber failure rate experienced. During VCSNS' most recent i inspection, eight snubbers were found unacceptable by visual inspection l out of a total population of 1127 TS snuisbers. These unacceptable i snubbers were subsequently tested, root cause analyses were performed, corrective actions were taken, ano were later decidred acceptable.

Deletion of tiie Reject line it. Figure 4.7-1 does rot contribute to any reduction in the margin of safety.

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