ML20006E248
| ML20006E248 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 02/08/1990 |
| From: | ALABAMA POWER CO. |
| To: | |
| Shared Package | |
| ML20006E247 | List: |
| References | |
| NUDOCS 9002220409 | |
| Download: ML20006E248 (18) | |
Text
{{#Wiki_filter:pg ' b ^ . l,$ . . , PLANT SYSTEMS. 3/4.7.9 SNUBBERS
'f
- LIMITING CONDITION FOR OPERATION-p 3.7.9 All snubbers shall be OPERABLE. The only snubbers excluded from this requirement are those installed on nonsafety-related systems and then Q
L. , only if their failure or the failure of the system on which they are-Og installed would have no adverse effect on any safety-related system. e k ". APPLICABILITY: MODES 1, 2, 3 and 4. (MODES 5 and 6 for. snubbers located on systems required OPERABLE in those MODES).
,o
( ACTION: With one or more snubbers inoperable, within 72 hours replace or restore.
~
i [ .the inoperable snubber (s) to OPERABLE status and perform an engineering evaluation per Specification 4.7.9.c on the supported component or declare q p the supported system inoperable and follow the appropriate ACTION statement
~
for that system. + ic l SURVEILLANCE REQUIREMENTS 4.7.9 Each snubber shall be demonstrated OPERABLE by performance of the following augmented inservice inspection program and the requirements of Specification 4.0.5. l a .' Visual Inspections I e < The first inservice visual inspection of snubbers shall be performed after four months but within 10 months of POWER t, OPERATION and shall include all snubbers within the scope of. 1 Specification 3.7.9. If less than two (2) snubbers are found I inoperable during the first inservice visual inspection, the second i inservice visual inspection shall be performed 12 months + 25% from I the date of the first inspection. Otherwise, subsequent visual I M. inspections shall be performed in accordance with the following I schedules ** j 1 No. of Inoperable Snubbers Subsequent Visual . per Inspection Period Inspection Period *# ) 0 18 months + 25% il L 1 12 months T 25% 2 . 6 months T 25% I 3, 4 124 days T 25%
, 5,6,7 62 days T 25%
8 or more 31 days i25% The snubbers may be categorized into two groups: Those accessible l and those inaccessible during reactor operation. Each group may be l inspected independently in accordance with the above schedule. 1
*.The inspection interval shall not be lengthened more than one step at a time. i
- The provisions of Specification 4.0.2 are not applicable. l
.J **-This'is a one-time Technical Specification change until startup from the p seventh refueling outage. Table 4.7-3 should be utilized during this interval to l
, determine the subsequent visual inspection period, t FARLEY - UNIT 2 3/4 7-20 AMENDMENT NO.
.;"' 9002220409 900208 M POR . ADOCK 05000364 *
' s,: P
'i PNU <
]) , , 4 .'
- t. c l
0 " TABLE 4.7-3
, , Snubber Visual Inspection Schedule l current' Visual Number of Inoperable Next Visual
' Inspection Periad* Snubbers Inspection Period #
18 Months 1-25% 0, 1, 2 18 Months + 25% i
. 3 12 Months T 25% 4 4 6 Months ~ 25%
0; " 5, 6 4 Months + 25% i a 7 2 Months 7 25% i 8 or more 1 Month-{25% 12 Months + 25%
~
0, 1 18 Months + 25% 2, 3 12 Months T 25%. i 4 6 Months 7 25% 5 '4 Months T 25% i u 6, 7 2 Months T 25%' 1 8 or more 1 Month I25% ] 1 l 6 Months 4 25%
~
0 12 Months + 25% 1 6 Months i 25% 2 4 Honths ~ 25%' 3, 4 2 Months 7 25% 5 or more 1 Month ][ 25% 4 Honths + 25%
~
0 6 Months + 25%- ~,- i 1 4 Honths 7 25% ; 2 2 Months I'25% 3 or more 1 Month 125% 4 > 2 Months + 25%
~
0 4 Months + 25% 1 2 Months T 25% 2 or more t 1 Month }[25% 1 Month + 25%
~
0 2 Months + 25% 1 or more 1 Month {25%
, . 4
# The provisions of Specification 4.0.2 are not applicable.
- Earlier visual inspections than required may be utilized. If this option is chosen, the criteria for determining the ne-t visual inspection period -
1, , shall be the criteria associated with the earlier visual inspection period selected. o
' i
, !FARLEY-UNIT 2 3/4 7-20a AMENDMENT NO. l l
4
\ ,1 L nw . - - _
s l, o . .;;' i . l, - = ,
=
- b Attachment 3 l SIGNIFICANT BAZARDS EVALUATION PURSUANT TO 10CFR50.92 FOR THE PROPOSED CHANGE TO THE l SNUBBER SURVEILLANCE RBOUIRENENTS TECHNICAL SPECIFICATION Proposed Change t This proposed change revises the visual inspection requirements of Technical Specification 4.7.9.'
Background
L l The Technical Specifications for Farley Nuclear Plant Unit 2 currently
- i. incorporates a visual inspection frequency table for surveillance of
- safety-related snubbers that was developed by the NRC as part of the Standard I Technical Specifications in 1975. This table is based on the assumptions and mathematics cited.in the " Note to Dennis L. Ziemann" from Mr. Joseph Sapir, l Operating Reactors, Branch #2, Division of Reactor Licensing, dated March 1, l- 1975. This document establishes specific statistical goals which were combined with an assumption of small population to generate the existing Technical specifications. Farley Nuclear Plant-utilizes a larger population which results- t y in an overly-conservative achievement of the NRC goal.- Therefore, Alabama Power E Company feels that current Technical Specification requirements for visual l inspection of safety-related snubbers are overly conservative and result in
- excessive surveillance requirements.
The Farley Nuclear Plant Technical Specification Bases state that functional testing requirements'for safety-related snubbers are based on providing a . L confidence level of 95% that at least 90% of the safety-related snubbers in the plant will be operable. The proposed modification to the Technical Specification snubber visual inspection surveillance requirements is based on the application of this statistical confidence level as the Technical Specification snubber functional testing requirements. The statistical methodology utilized employs a mathematical model which is used to determine the appropriate visual inspection interval. A chi-square distribution is used to estimate the individual snubber failure rate. The ' l exponential distribution is used to predict the probability of a single snubber i being operable. A binomial distribution can then be applied to the entire snubber population to determine the percent of failed snubbers which corresponds to particular current and next visual inspection intervals. The details and results of this analysis are provided in the Enclosure to this evaluation. l r
>j
[f . ' ' l
m
. .([
- At tcchment 3
.. Signific:nt H:zards Evolu tien Purcu:nt to 3 '.
10CFR50.92 for the Proposed Change to the Snubber Surveillance Requirements Technical Specification
, Page 2 , This proposed Technical Specification change involves only visual surveillance l requirements and does not alter the current Limiting Condition for Operation or the accompanying Action Statement for the snubber system. The statistical methods employed as the bases for the proposed Technical Specification change vill not be used to alter the current Technical Specification requirement that all safety-related snubbers be operable or as justification to allow a snubber to remain in an inoperable condition. Furthermore, the conservative Technical Specification requirement to visually inspect 100% of the safety-related snubbers will not be altered. Also, the March 30, 1987 approval was based on a
- , . conservative smallest population size of 200 anubbers. This change request would effectively be applicable only to the Unit 2 inaccessible sntbber
. population which exceeds 400 anubbers.
Analysis Alabama Power Company has reviewed the requirements of 10CFR50.92 as they relate to.the proposed change to the snubber visual inspection requirements and considers the proposed change not to involve a significant hazards 3 consideration. 'In support of this conclusion the following analysis is provided (1) The proposed change vill not significantly increase the probability or consequences of an accident previously evaluated because the existing snubber operability requirements will remain intact and the proposed visual inspection requirements vill effectively verify
, snubber system reliability. In addition, a plant shutdown (transient) vill not be required to inspect inaccessible snubbers.
(2) The. proposed change vill not create the possibility of a new or different kind of accident from any accident previously evaluated because the change vill not alter plant configuration or' change
, parameters governing normal plant operation.
L (3) The proposed change vill not involve a significant reduction to the margin of safety because the combination of visual inspection - intervals which maintain a 95% confidence that at least-90% of all safety-related snubbers are operable at all times along with the required functional testing of safety-related snubbers vill provide adequate assurance that the snubber system vill adequately perform its intended function. Conclusion l Based upon the analysis provided herewith, Alabama Power Company has determined that the proposed Technical Specification change vill not significantly increase the probability or consequences of an accident previously evaluated, create the possibility of a new or different kind of accident from any accident previously evaluated, or involve a significant ! reduction in a margin of safety. Therefore, Alabama Power Company has [ determined that the proposed change meets the requirements of 10CFR50.92(c) and does not involve a significant hazards consideration.
.c
r-e
.=
f:- ...
,. . 4 t
9 4 I Enclosure to Attachment 3 i c .. Statistical Evaluation of Snubber Visual Inspection Frequency t l.> s i 's
>t0 .
p/ t 4 6 I 1 9 l P f" k,
*Ie' lt i,
t s .1 . 1 3;
- p. .
I I V!SUAL !NSPECTION PROGRAM FOR SNUBBER OPERABILITY SURVEILLANCE I J TABLE E CONTENTS 1.- INTRODUCTION
- 2. DERIVATION OF PROBABILISTIC MODEL FOR RELIABILITY ANALYSIS
'(. -
- 3. ESTIMATION OF PARAMETER
- 4. DETERMINATION OF VISUAL INSPECTION PERIODS 5.
VISUAL ~ INSPECTION PROGRAM
- 6. CONCLUSION
- 7. REFERENCES TABLE 1 VISUAL INSPECTION SCHEDULE FOR ANY GROUP (CATEGORY)
.0F FNP SNUBBERS I
1 t-
., -_s~. _ __._ _ _
,4 . .
..- : )
r l
~v!sVAL INSPECT!0,,N PROGRAM FOR SNUBSER OPERABILITY SURVEILLANCE o
- 2. _
INTRODUCTION l-The objective of this study is to establish, based on probabilistic and statistical methodo1gies, 'a visual i lnspection program to maintain the reliability of the
. snubber. operability at a required level for the Joseph M.
Farley Nuclear Power Plant (FNP) Units 1 and 2. The required reliability level is specified by the following reliability criterion: .
'To establish a visual inspection schedule to verify at a 954 confidence level that a minimum of 90% of the '
snubbers in a group or' category are operable all the time". . L l Note that the above reliability criterion is based on L maintaining a minimum level of snubber operability at all - times and conservatively does not take the probabilistic , nature of the unlikely occurrence of a design basis event l l , (DBE) into account. i l I 2. DERIVATION 9I PROBABILISTIC MODEL ggR RELTABILITY ANALYSIS i l Consider.a group of snubbers. Let n denote the total L number of snubbers'in the group. Let X denote the random variable representing the time-to-failure (or operable life r span) of any individual snubber in the group. P In this study', the random variable, N, will be assumed to follow the exponential distribution. Owing to all t
. categories of the snubbers in.both of the FNP Units 1 and 2 l having'long been periodically inspected and maintained, their hazard (time) functions (as defined by Eq.3-40 on '
Pg.103 of Reference 1) will virtually not fluctuate with L the time'between two consecutive visual inspection periods. Because the hazard function of the esponential distribution also does not fluctuate with time (as exhibited by Eq.3-42 on Pg.105 of Reference 1), it significantly indicates that i the exponential distribution is appropriate for representing the time-to-f ailure of the snubbers. ( 2 -
l
- p. .
Furthermore, per Pg.105 of Reference 1, the exponential distribution la the most commonly used to represent the time-to-failure of a system. It plays a central role in
.: reliability, comparable to that of the normal distribution 1 in other applications.
- 1 since X follows the esponential distribution,"its U probability density function,.ig(x) and probability ,
w distribution, Fg(s) are ; r e e '*
, , sac,#>0 f "(8) * '
(1) o , efhegwise a rt- e" ,aao F(n). K P{ x ( *) . f f (tid; . i
. (2)
- se K '0 , Ofht4wt5e l
l i( vhere the parameter e is physically referred to as Lhe f ailure rat e (number of f ailures per unit of time). Per Pg.107 oTleference 1, the mean or expected value of X, at can be' expressed as - *
- l L .,= (3)
. Physically, og'is referred to as the 23,mean time-to-failure.
Let Pa, be the probability that any individual snubber in
- the group fails before or at (any) time, t. Hence per Eq.2, P3 can be expressed as P5 = P(X 1 t ) = 1-e * (4)
Let 2 be the random variable denoting the number of failed snubbers in the group before or at time, t. Since L the time-ta-failure of each individual snubber in the group takes place independently of the other, the random variable ! I E follows the binomial dtstribution, namely, 3 l-1
,.4 .
I a
. P(z e :) = (n)P, , ( 8 - P,)n-s (5) where -
in , n! .
. La ) * !(n-a)! (6)
Let P(E i S) km the probability that there are no more l j than S snubbers in the group inoperable before and at time, 1
- t. Because E is a binomial random variable, P{E <s) ~
can be espressed as S a ! P{2($)=,{,(n,, ,P, ( 1 - P,)n - a , (y
)
The snubber reliability criterion (specified in. ) l Section 1) of having a 954 confidence level that there are i a minimum of 90% of the snubbers (in the group) operable j l before and at (any)' time, t, is equivalent to having a 95% y'
- confidence' level that there are less than 10% of the anubbers (in the group) inoperable before and at (any)
.J c
time, t. Therefore,.the latter (or equivalent) reliability criterion will be employed for the advantage of reducing numerical computation effort needed later. In order to l obtain at 95% confidence level that there are less than 10% 1 of (any)the snubbers time, t (in (a)the setgroup)in PiEIS)Eq.7 equalinoperable before and at <
- to 0.95, i.e.,
l ! s n-r , o.95 (E) p{Z ( $) = ,1,(n)p, 3 ( 1 - P, ) u l and (b) set the value of 5 in Eq.8 equal to the largest integer that is less than 0.1n. By substituting Pg from Eq.4 into Eq.8, Eq.8 becomes , P{ 2 4 s) = h. o (n ))(* - *-et 3 a
)
s( a-et n-s(9)
= 0 45 e
[ 4 l 1 l
^ ^ ^ ^
e , V . .
,e 4
- f. .
Eq.9 will be the basis for the reliability analysis to ' develop the required visual inspection schedule in factions 3 and 4.
, . 3. EST!MATION SI PARAMETER .
In order to be able to evaluate the probability, : p(E < 8) in Eq.9, the value of the parameter e must , be iTrst estimated. Let T denote a visual inspection period for the group (with n snubbers). and let I denote the total number of inoperable snubbers found in the group per visual inspection period T. Also let In denote the lower confidence k und estimate of og (the mean time-to-failure) at the (1-4)100 percent confidence level. Per ; Eq.3-46 on Pg.107 of Reference 1, og can be expressed r as
=
m 27 '
- s (10)
X s-s,31, a I. whereTf...t+ is the Chi-Square value at (1-d)100 th percentile at 22+2 degree of freedom. Per Eq.3-43 on , E P9 107 of Reference 1, 7 is the sum of the actual operable time from every snubber in the group per inspection period and can be conservatively expressed as t
, Jr= (n-1)T (11) l --
Eq 11 provides the conservative 7 because all the l inoperable snubbers are assumed'to fail at the l beginning of the visual inspection period, T. In 1 p reality,ime at any t between 0 and T.an inoperable snubk r can Note that13.e,trta maybe h come inoperable 7 obtained from table IV on Pgs.314 and 315 of Reference 1 , for 21+2 6 100. a By substituting 7 from Eq.11 into Eq.10 Eq.10 becomes l v f(n- 3)T (12) m . x
' x's-s , s s 4 2 i
( 5
.o
y., a
- w. .
[. Let I denote the upperat confidence bound estimate of e (the j the (1-4)100 percent coniidence anubber level. failure rate)Per Eqs.3 and 13, $ can be espressed as ul) 2(n-3)T . By substituting e in Eq.9 by $ from Eq.13, Eq.9 becomes 3 s
#g.g,f t + 2 I'
- E . 8 3 ' 8 y ,
(34) a(n-1)T yn_2,,4, h o(1+- t - "I"
) (8 P{ I ( 5 ) s= k.
j Eq.14 can be used to established the snubber inspection schedule (corresponding to the reliability criturion I specified in section 1) as described in section 4. i J I
- 4. DETERMINATION 91.V!sUAL INSPECT!ON PERIODS Eq.14 in section 3forcan be used to determine the visu specified in section 1) a group of snubbers. For a iven group of n snubbers, at the end of each visual '
fnspectionperiod,T(whichwillbereferredtoasthe current visual inspection period and denoted by Tc from now on), the total n e er of inoperable snubbers, 1, is found. L^ Mence, the statistical. estimate, 6, for the current inspection period can be found per Eq.13.. Assume that therema snubber failure rate (e) Substitute the the end of next visual inspection period.Then solve for t from values of n. T=Tc 'and I into Eq.14. inspection Eq.14. The value of t obtained will be the next such that i period (which will be denoted by tu from now on) minimum of 90% of snubbers in the group are operab the time is satisfied. In this study, the upper confidence bound estimate (e) of the snubber failure rate (e) at By thesubstituting 95% confidence yV level will be used, i.e., a(=0.05.and tatw into Eq.14, Eq.14 becomes e(=0.05, T=Tc . ( L 6 l- . -- -. - . - - _ . . . . - _ -- _ . . _- . _ ___ _.__ _ ._
.L . J ,
. . i
)
~ .
=
8 g e b _ ( 8 ("i ) *'/S(ea, e"'] t.):c P.{Z4S) = see(,a)(f-# - I *a*("n > se.H u'"T' (15)
)b}"-
At mentioned before for Eq.8 in Section 2, 5 is the , ;
- largest integer that is,less than 0.In. t Note that Eq.15 shows that the next visual inspection ,
period satisfying the reliability criterion for a
~ * -' snubber group depends on both the group size (n) and the total number of inoperable snubbers found (!) i by the end of the current visual inspection period. .
Therefore, in accordance with Reference 2 the existing '
~, procedure specifying the nest visual inspection periM h sed.on the n @ r of inoperable snubbers found per the '
current visual inspection period alone is overly ' conservative for tie group with large snubber populations '
; and results in excessive surveillance.
- In order to facilitate establishing a visual inspection schedule. table, the following properties of Eq.15 can be '
utilised. (a) By fixing the current visual inspection period (Tc), < l the percent of inoperable snubbers found (r) which is L (1/n)100, the maximum. percent or number (s) of the I snubbers (in the group) allowed to be inoperable at . L - any time, and the confidence level (c) of estimate of the maximum percent of inoperable snubbers (in the
. group).at any time, the larger the snubber group size (n), the longer is the next visual inspection period, tn. This is because per Eq.13, the larger the value of n, the smaller is the statistical estimate of failure rate, 9.
(b); ty fixing n, r, s and c as defined in Item (a) above, the longer the current visual inspection period (Tc), the longer is the next visual inspection period (ts). L This is because per Eq.13 the larger the valye of Tg, L the smaller is the estimate of failure rate e.
)
. 7
<w *-----
4 l
. l l
[" 5. v!sUAL' INSPECT!0N PROGRAM t By employing Eq.15 and its properties (a) and (b) in J Section 4, a snubber visual inspection schedule is established for any group (category) of the snubbers of the FNP Units 1 and 2 and is.provided as Table 1. As per Eq.15, the visual inspection schedule vi11 ensure at
. a 954 confidence level that a minimum of 90% of the snubbers in each group is operable (or equivalently less :
than 10% of the snubbers in each group'is allowed to be inoperable) at any time. It is emphasised that the following conditions have been conservatively imposed in the derivation of.the visual inspection schedule (Table 1): (a) In order to obtain the shortest tw for a percent of t inoperable snubbers found (r), picked for trials in the : process of constructing Table 1 and based on Property (a) , l of Eq.15, the smallest snubber group size (n') associated with each value (picked for the trials) of r < must be used. Such smallest corres pnds to I = 1r'namely,n'group is to size (n') be computed L from the equation, rn /100=!=1. k (b) ForaspecifiedcurrentvisualinsactionboundofTeriod.(T); based on Property (b) of Eq.15, th lower , is used in the process of constructing Table 1. For example T = 18 months + 25%, the value of T = 18-0.25x18 = 13.5 months Ts used. l (c) For a specified next visual inspection period (t), the l upper bound of t is used to calculate the confidence level (l'.e., the left hand side of~Eq.15). For example t = 12 months + 25%, the value of t to be used for computing the confTdence level is t = 12 + 0.25x12 >
= 15 months. Note that the higher the value of t, the lower is the confidence level.
In addition, in order to avoid the influence of a short inspection period effect as discussed in Reference 2, the next visual inspection period in Table 1 is conservatively allowed to increase only one step above the current visual inspection period regardless how small the percent of inoperable snubbers found per the current visual inspection period may be. 8
,,a - , - , . - , , - , , , - - , , , .
- f. :' .>.
f 4 p' - - As discussed in Item (a) in section 5, for each upper bound , value of r in Table 1, a corresponding minimum snubber.
, group size is required in order to obtain the shortest next visual inspection period. For all the upper bound values of r in Table.1, the corresponding values of the required-minimum group size range from 31 to 200 (except for r=0, the smaller the r value, the larger is the required minimum group size). Hence, it is conservatively required that Table 1 is not applicable for the snubbers with group size (n) smaller than 200. -
0 In meeting the reliability criterion-as specified in section 1, L the safety related snubber population may be treated as.a. single I group or may be categorized into two groups: These accessible
- and those. inaccessible during reactor operation. Each group may ,
be inspected independently in accordance with the determined schedule. l-l t [ 6. CONCLUSION L 3 L In this study, a set of visual inspection schedales to ensure at a 95% confidence level that there are a minimum of 90% of the snubbers in each snubber group or category of , the FNP being. operable Q ihg hm has been developed as ; [ exhibited in Table 1. This visual inspection schedule has been derived based on the probabilistic-and statistical l methedologies as described in sections 2 and 3 including justification for all assumptions used. Additionally, l the_conservatisms used in the course of developing the visual inspection schedule are pointed out as they are applied. In particular, the snubber reliability criterion (specified in section 1) is based on providing a minimum levellof snubber operability at all times and conservatively does not take the probabilistic nature of the unlikely occurrence of a design basis event into account. l It is emphasized that based on the reliability analysis in this study, the next. visual inspection period satisfying l reliability criterion (specified in section 1) for a L snubber group depends on both the group size and the total , number of inoperable. snubbers found by the end of the current visual inspection period. Hence, the existing FNP procedure specifying the next (subsequent) visual inspection period based on the number of inoperable snubbers found per the current visual inspection period alone is overly conservative for snubber groups with large populations, results in excessive surveillance, and should be replaced by the visual inspection schedule (Table 1) developed in this study. L 9 1
= . . .. J
. j The details for the derivation and utilization of the
' proposed visual inspection: schedule listed in Ta ble 1 (for each snubber group of the FNP Units 1-and 2) have been provided in section 5. .
In conclusion, a visual inspection' schedule to verify at a 95% confidence level that a minimum of 90% of the snubbers in a group or category are operable all the time has been developed on the bases of rigorous statistical analysis and' , assumptions including various conservatisms. This snubber i visual inspection program is proposed to replace the existing program for the FNP Units 1 and 2. ( 1 l' d' 4
'h t
I i i e 10 4
h < ; . 7, , . . . :
., l
.g' a 1.
o
- 7. . REFERENQH ,
c 1. H Nahn, 0.-J. and shapiro, S.S., " Statistical Models in Engineering *, John Wiley and Sons, Inc.,' New York, New ' York, 1967
- 2. ' Technical Sgecification for snubber Operability and Surveillance , Note dated Narch 1, 1975 from Joseph Sapir, operating Reactors Sranch 02, Division of Reactor Licensing, the U.S. Nuclear Regulatory Commission (U.S. NRC) to Dennis L. Elemann.
L t l' i \. . I i 9 l
~
11 r s 4
'k
's.
, 1
~
.s\ 1 L. ;. .. ,
. . y
. ,. 1 V
's - 1
( , TABLE 1 j visual inspection schedule for any group (category) of snubbers l of the Joseph M. Farley Nuclear Power Plant Units 1.and 2. Current visual l Percent of Inoperable Snubbers ' Next Visual Inspection l found (r) per Current Visual ' Inspection Period
- Inspection Period Period l
24 months i 25% r 1 0.76% 24 months 1 25% 1 24 months i 25% 0.76% < r 1 0.99% 18 months + 25% ' l 24 months i 25% 0.99% < r i 1.40% 12 months 1 25% 24 months 1 25% 1.40% < r i 2.43% 1 6 months 1 25% - l 24 months 1 25% r > 2.43% l 3 months i 25% 18 months 1 25% r 1 0.62% 24 months 1 25% 18 months i 25% l 0.62% < r 1 0.76% 18 months 1 25%- k 18 months 1 25% 0.76% < r i 1.09% 12 months i 25% [ 18 months i 25% 1.09% < r 1 ,1.96% 6 months i 25% 18 months + 25% l r > 1.96% , 3 months i 25% i .................................................... __................___ 0.58% 18 months 1 25% 12 months 1 25% i r1 12 months 1 25% 0.58% < r 1 0.76% 12 months 1 25% 12 months 1 25% 0.76% < r i 1.40% 6 months i 25% 12 months 1 25% i r > 1.40% i 3 months 1 25% < 6 months i 25% r=0 l 12 months i 25% l , l 6 months 1 25% 1 - 6 months i 25% 0 < r 1 0.76% 6 months 1 25% r > 0.76% 3 months 1 25% l 1 l (. 12
p ..
;s:
.. g. .. ,,
- . - j I: '--
hi ~ ' Table 1.(Cont'd) 6 .......................................................................... CurrentLVisual Percent of Inoperable Snubbers Next Visual
-Inspection found (r) per. Current Visual -
Inspection Period-* Inspection Period . Period
,n g , . .................. .................................. ....................
3' months"1 25% r=0 6 months 1 25%
- 3. months 1 254- l r>0 3 months 1 25%
1 s t L 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. ( Earlier v'isual inspection periods than required may be ,
utilized. If this option is chosen, the criteria for determining the next visual inspection period shall be the o 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. c M L o P 10 4
?
( 13
--n- - - . , ,-}}