ML030360306
| ML030360306 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 02/04/2003 |
| From: | - No Known Affiliation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| Download: ML030360306 (28) | |
Text
JANUARY 23,2003 NRC MEETING RI-ISI RELIEF REQUEST CLARIFICATION ON THE USE OF SUB-SEGMENTS Meeting Agenda Kick-Off and Introductions ........... Bud Gerling, RegulatoryAffairs Supervisor PalisadesNuclear Plant Palisades Application of Methodology ........................ Mike Carlson,ProgramsEngineeringManager PalisadesNuclearPlant Westinghouse Overview of Methodology............ PaulStevenson, PrincipalEngineer Westinghouse Electric Company LLC Palisades Responses to Clarification Request Summary of Requested Item #1 ................................... Bruce Bishop, PrincipalEngineer Westinghouse Electric Company LLC Summary of Requested Item #2 ................................... Dick Haessler,PrincipalEngineer Westinghouse Electric Company LLC Summary of Requested Item #3 ................................... Mark Cimock, Senior Engineer PalisadesNuclearPlant Conclusion .............................. Mike Carlson, ProgramsEngineeringManager PalisadesNuclearPlant ATCAHMENT
PALISADES RISK-INFORMED INSERVICE INSPECTION PROJECT CHRONOLOGY
- October 1999: Project Kickoff / Expert Panel Scoping Session.
- Development of engineering analyses (EAs) for segment definitions and associated direct and'indirect cOnsequenCes.....
"* Development of Win-SRRA failure probability analyses.
"* Performance of CDF/LERF analyes for.all direct.and indirect consequences .
on all segments modeled in the PSA.
"* Performance of risk ranking analysis.".:, ,
"* October 2000: Expert Panel Risk Ranking Meetings for categorization of-high safety significant (HSS) and low safety significant (LSS) segments.
"* Change in (Delta) risk analysis.
- Statistical selection of number of wefds 6obe Inspected (Perdue Analysis)..,_
"* Revision (by Palisades) due to segmentation/consequence changes bnm select .
systems. Revisions perfopedon:- .,_
o Segmentationi/Cnsequence ana alyysis. -.
"o CDF/LERF analysis ...... ....... ......... .. ..
"o Risk Ranking analysis (Expert Panel reconvened).
"o Delta Risk analysis. .
"o Perdue analysis.; .
- . ,' * ;*" , . " : . F
"* Selection of inspection locations and methods by Engineering Sub-Panel.
"* March 2002: RI-ISI submittal to the NRC.
- 5. . ............ o...... .
"* May 2002: Request for additional information (RAI) issued by NRC.
"* August 2002: Palisades response to May RAI.
"* September 2002: NRC Audit of Palisades RI-ISI Program.
"* October 2002: NRC submits draft of Request for Clarification on the Use of Sub-Segments in the RI-ISI Relief Request
- January 2003: Palisades, Westinghouse, and NRC meeting to discuss open Request for Clarification on pipe segment modeling.
I
OVERVIEW OF WESTINGHOUSE OWNERS GROUP APPLICATION OF RISK-INFORMED METHODS TO PIPING INSERVICE INSPECTION (WCAP1 4572 REVISION 1-NP-A) RELEVANT TO TODAY'S DISCUSSION a) The methodology identified in WcAP-I4572 is a risk-informed methodology incorporating both quantitative and qualitative (i.e.
deterministic) aspects.
b) The quantitative portion of the process uses bestestimates that in some cases, may be conservative but not overly conservative.
c) Segments are defined primarily on the direct consequences associated with a postulated piping failure.
d) Failure probabilities are calculated for each segment for use in generating a piping core damage freqbency (CDF), large early'release frequency.
(LERF), risk reduction worh (RRW)Y and other risk metrics to help determine the safety significance of each segment.
e) All segments determined to be high safety significant by the expert panel receive examination. ;* .- ,,-
f) For high safety signific-ant se;gmments, 100% of alwelds subjected to an active failure mechanismS'or analyzed as being-highly susceptible to an active failure mechanism-are examrned.-"
g) The Perdue model analysis Is-used only on th6se Welds in high safetyý significant segments whereithere is noactive failure mechanism and the welds were not analy'zed as being highly susceptible to an active failure mechanism. The Perdue Model is not used for socket welds...
h) Westinghouse provided training, technical review of Palisades' work, and worked closely with Palisardes throu-gho-ut their RI-ISI program to assure that Palisades correctly applied the methodology in WCAP-14572. ..
Requested Item
- 1. Forthe failureprobabilityestimation for segments that were subdivided,please provide the definitions used to identify sub-segments. Also please explain how the failure probabilityestimates are developed for a segment that has been divided into sub-segments and how your methodology comports with the approvedmethodology. - - .
Summary of Palisades Response, :
a) Sub-segments within a segmnent are defined based on having the same consequence but having different pipe sizes.'
b) The segment probability is the-highest Value of the failure prbbabillities . .
estimated for all its sub-segments.
c) Palisades application of thfemethodology fully Comportsvith the approvd methodology for the following reasons:-,,
"* SRRA calculations on'the senisitivity ofpipe size, including the presence'of butt or socket welds, are performed to ensure excessive conservatism does not unrealistically impat tlhe- risk'categbrization of the segment-
"* When multiple degradation mechanisms exist in a sub-segment, limiting input values for each mechainismrare combine:d. -- ,
"* The failure probability ifor the segment is characteirized as the highest sub segment value, which-is the worst-case situation in each segment.,
- The results of the SRRA calIculaitions forsub-segments ard sdgments re reviewed by the engineering team relative to bein reasonable and consisten with operating experience-.. **" g raonable a consistent
" Use of the same four Considerations in sub-segment failure probability.
(configuration, components, materials/chemistry and lads) also inslr.teisthatl.-.
excessive conservatism is'not applied to the selection of inspection locations.
" All requirements and guidance on probability estimation by the engineering team with the SRRA tool in the approved WCAP Report, its Supplement and the NRC-SE are fully considered.
Requested Item
- 2. For the Perduemethod applicationon segments that were subdivided,please provide the definitions used to identify sub-segments. Also please explain how the Perdueinput parametersare developed for a segment thathas been divided into sub-segments, how the results are-usedto determine the number of locations for inspectionin the segment, an~d how your methodology comports with the approvedmethodology.
Summary of Palisades Response The Perdue Model is used to aid in the determination ofthe number of inspection locations for segments determined to be high safety significant by the plant RI-ISI expert panel. Palisades segments were divided into sub-segments (or lots) during the Perdue :
Model evaluation using the following cases; -.
Case A K Segment has one pipe size, active failure mechanism postulated - susceptible locations are selected for inspection. Active failure mechanisms are removed from, the Perdue Model inputs. The Perdue Model is used for remaining locations.
Case B Segment has more than one pipe size, P!o.active.failure mechanism postulated - first approach is to use conservative input parameters and run the Perdue Model on all welds. Ifthe results are too conservative, then-subdivide the segment into lots, by pipe.
size, run the Perdue Model on each pipe size', and mnJltilyconfidences of each lot to check against the acceptance criteria.
Case C -.
Segment has more than one pipe size, a;ctivelailure mhecha'nism postulated susceptible locations are selected for inspection. For.the remaining locations, active, failure mechanisms are removedfrom thePerdueModel inputs and the first approachis to use conservative input parameters and run the Perdde. Model on all remaining welds'.
If the results are too conservative,'then subdividethe segmnent intolots by pipe size, run the Perdue Model on each pipe size, and multiply confidences of each lot to check against the acceptance criteria. . f.. "".......
The above cases used in the Palisades R-lSlIprogram are consistent with the methodology described in WCAP-1 4572, Section 3.7.
Requested Item .....
- 3. Myou were to apply the failUre probability estimationand the Perdue methodology to the entire segment forall segments,'as opposed to sub segments, how would the totalnumber of inspections requiredin the RI IS program change?
Summary of Palisades Response The total number of inspections wouild not change.
Program specific data wasevaluated to address this-request., There are*193 segments that contain multiple pipe diameters and have some variationi In the SRRA input parameters. All of the segments with SRRA input parameters that "'
vary fall into one of three categories:
- 1. Only'vlaateion in inputs are pipe size and wall thickness (119 segments)
The only variations in the InputS- re tl6oser&ssociated with the actual, phsical makeup of the pipe. -All other7SRRA inputs are thesafne for'each-'sub-segment,f
- 2. Variations are all related to pipe and weld geometries (65 segments)
The more limiting inputs were consistently applied to thesmatl-bote socket-welded sections of these segmedts' NNurneroUs exarmples sihw that- - '
reevaluating the large bore sedions of ftepipb with the most-limiting inputs' would raise the failure probabilities'f6r-those sub-segments. However, in each example, the original limiting failure probability (for the small bore piping) associated with the segment remained the highest value and would still be chosen to represent the segment. Based on the evidence from the examples, applying the failure probability i~nate-s~oth6 entii'esgrient as op'posedtoo "' *' " ':
sub-segments for those in'this' category would not-ijicrease the ndimber of .. . ' "
inspections. " '
.:.'w. .
C" " ' - ' 'i- ..
- 3. Varations are based on engineenng judgment regarding' potential':- -..
degradation"mechanisrs (nine segMehts)
The justification for the variation in the Inputs for these segments is sound and well documented. The decisions 'fo thinputs" derebasedon kinown-d-studied conditions specific to'each ection of thýe'-pipe.".--A-dditidnal because the segments in this category are low safety significant (LSS) and the most conservative failure probabilities of the sub-segments were used, had the segments in this category been split, the new segments would have also been LSS and there would have been no change to the number of inspections.
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE
- ENCLOSURE NUCLEAR MANAGEMENT COMPANY, LLC PALISADES NUCLEAR PLANT DOCKET 50-2S5 REQUEST FOR CLARIFICATION ON THE USE'OF SUB-SEGMENTS': :
IN THE RISK-INFORMED INSERVICE INSPECTION -RELIEF REQUEST .,.
PALISADES NUCLEAR PLANT 45-DAYRESPONSE .. . -t
., ** , *. ,. I :' . " , . - ' * " : .' : " ' .
S-..- ,..
- 1' -I.,?.,,
"2 2.-. " : .:P"--a,-ges t.; l : .- .*.:', '*. :..... ,':,,.o "-.,.:-- '.... .' .
- . .1.. -r - * -
S. . . . .I -, .=- ... ..
.. " ..: ! ; " " ,; "" : 4.............., ..-", .... : ;* Z :*
REQUEST FOR CLARIFICATION ON THE'USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE.,
Introduction Duringa September 12-13, 2002, site auditof the risk-informed documentation to support your Inservice Inspection relief request, we noted that bumerous ,
segments were divided into sub-segments, failureprobabilityestimates were developed for one or more of the sub-segments, and the failure probability: .
estimates of one of the sub-segments was used for the entire segment Page 71 of the WCAP states the following.
"MThe failureprobabilityof a segment Is characterizedby the failure potential(probabilityor frequency as appropriate)of the worst case situationin each segment (not a selected weld in each segment). This is calculatedby the SRRA code by inputting the conditions (typically, the most limiting or bounding)for the entire pipingsegment. Essentially,the piping failure probabilityIs a representationorcharacterizationof the-.
pipingsegment."
Our understandingis that your methodology applies this guidance to individual sub-segments but not to the entire segment and therefore deviates from the approvedmethodology.
There was also some discussion of your applicationof the Perdue methodology.
We were informed that the Perduemethodology Is also appliedIndependently to individualsub-segments. Pages 170 and 171 of the WCAP discuss application of the Perduemethodology. The relevant text is provided below.
"Seqment#: This is the name for the lot from which a sample of structural elements (such welds, pipe elbows, branch connections,etc.) is to be taken. Generally, eachpiping segment is defined as a lot. However, segments that are similar (e.g., all the cold legs on each reactorcoolant loop with the same postulatedfailure mechanism) may be combined to define a lot.
Number of Welds or Elements: This Is the number of structuralelements in the lot Probabilityof a Flaw (Ospecified year!weld): The probabilityof an unacceptableflaw in the segments 'mostlikely to fail' weld (or typical weld, ff they are viewed as clones) at the currentage of the weld (usually the currentage of the plant unless the pipe has been repairedor replaced).An unacceptableflaw is defined by the ASME Section Xl Code.
This has been defined as a4 > 0. 10 and is obtainedfrom the probabilistic fracture mechanics code (e.g., SRRA)."
2
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY-RESPONSE Our understandingIs thatyoUr rmeth6dology applies this guidance to Individual sub-segments but not to the entire segment and therefore deviates from the approvedmethodology "
At the exit meeting of the audit, we noted that supplementalInformation regardingthe use of sub-segments Will be needed to complete the review of the relief request. We therefore request the following Information.
Requested Item
- 1. For the failure probabilityestimation for segments that were subdivided, please provide the definitions used to identify sub-segments. Also please explain how the failure probabilityestimatesare developed for a segment that has been divided Into sub-segments and how your methodology comports with the approvedmethodology., '; ; , * !. !.-f ...,!:
Response
Failure consequences were used as the primary factor toInitially divide segments ....
Into sub-segments. This method led to some Individual. piping segments consisting of piping with a variety of pipe diameters. For example: a four-inch diameter pipe with a two-inch diameterbranch line may be part of the same-.,,:"
piping segment ifa failure at any portion of the segment Would result in the Same consequences. For multiple pipe size sergments;-sub-segments were defined by.
the pipe size for the failure probability analysis.-
The failure probability estimates were devblopedfor a-se&grneht that has been divided Into sub-segments using the Westinghouse Structural Reliability And Risk Assessment Model (Win-SRRA). Some of the input parameters used by-the "
Win-SRRA code vary ff the diameter of the pipe Vadres (e.g:nomInal pipe size, ,-
thickness to outer diameter ratio). Failure probability estimates'forsegmrents. - '. ,. .;
made up of multiple pipe sizes were determined by-performing multiple Win-SRRA cases. In instances with multiple cases, resulting In multiple failure probability estimates, the highest failure probability, associated with the segment: '. . 2.. ...
was then used to represent the segment.'-.
For each case, the Win-SRRA code required 18Input paiameters associated .," -",:;
with the piping. For segments with multiplepipesizes, some of the Input -.-'
parameters varied from case to case even though they represented the same ' ..
segment. Different pipe diameters required different Inputs for a number of the " ' - :.
parameters. Other Inputs also varied based on expert engineering judgment-,- . .. ".
Palisades subject matter experts in in-service inspection (ISQ),-non;destuctive.', -: .' .,.. ;. ;
examination (NDE), materials, and pipe stress analysis.worked togetherto"; J.
develop the input parameters for each Win-SRRA code case run. Therefore, 3
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE each case represented a sub-seg'mentand was evaluated for-the expected conditions forthe sub-segment. -
Following the Westinghouse Owners Group WCAP-14572, 'Westinghouse Owners Group Application of Risk-Informed Methods to Piping Inservice Inspection Topical Report,* Revision l-NP-A and WCAP-14572, Supplement 1, "Westinghouse Structural Reliability and Risk Assessment (SRRA) Model for.
Piping Risk-Informed Inservice Inspection,* Revision 1-NP-A (referred to as "WCAP-14572"for the remaindei of this document) methodology, the group developed limiting Inputs for evaluation of each segment or sub-segment. Input parameters varied for separate portions of the samesegmenrtfor one of two '
reasons. One reason was that many segments contained multiple weld, .
geometries (both butt and socket-welds). :In these segments specific geometries were reviewed. Different parameters to'accurately model the geometry were Input. Basic design practice would also'suggest using more limiting Inputs for *;.
dead weight and thermal stress, and design limiting stress for small bore (socket-welded) piping, where spacing tables were utilized In the routing design versus actual analysis results. The other reason was that Input parameters for sub-segments varied slightly basid on engineering judgment, For thesetcases-' '
the inputs were developed by plint-subjectmatterexperts and were based on:
observed and recorded conditions. .The basis fo0reach Judgment is documented in the Palisades Win-SRRA engineering analyses., Though thie Input parameters:
for different cases of the same segment may vary, the parameters that were' ,
chosen for each case were the most limiting for thtat section0 of the piping segment. The limiting failure probability-estimates associated with 'each pipe size for each segment are based on the realistic limiting inputs associated with that section of piping. For segments With multiple line'sizes; rMiultiple failure ', - hr ,
probabilities were determined. IrV every case the Most rlihiting (highest) failure' . .- " , ,
probability associated with the segment was'used to repteseht the segment. - . . ,.?
\ ,',-
- -$ '*-/ , *,.. ..' i**'.. -, -
- , '*i ; : :i' ! 'I ,. . .- : .* ",=. . . , -. : -, . -.
As shown In figure 3.5-1 and the'aCcompanying-text in-thl'eepproved - * ' ; . - -,
I WCAP-1 4572, failure probability estimation Is the reisponsibility of the - .
engineering team based upon theiibknbwledge of the pertinent inforimation at.. , ,.![
their plant and any potential concerns identified In Industry experience at other "
plants. For example, recent PWR plants have evaluated the Increased potential for stress corrosion cracking at the reactor vessel outlet nozzle weld based upon the leak at V. C. Summer. The SRRA tool ls used tolquantify the effects'of the . ... ' '. ,
engineering team's input on the Calculated leak anid break probabilities.;.: -
The second concern of the summary and concluslins of-the Nuclear Regulato . .
Commission (NRC) safety evaluation'(SE),(Sectioh A.25,on-page A-21) forthe :: "-.U' .
SRRA tool (supplement i to the approved WCAP1 4572) endorses this position *.' *r;:. t via the following: .. ' - - - ,- . . " - ..
4 31
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE "The results of SRRA calculations should always be reviewed to ensure that they are reasonable andcconsistent with plant operating experience. Data from plant operation should be used to review and refine inputs to calculations.'
Nuclear Management Company's (NMC's) application of the methodology, taking the limiting SRRA probabilities from the sub-segments of different sizes In a segment, comports with the N1C approved methodology. . ,--
The fifth concern In the previously cited section of the NRC SE recommends:
"The simplified nature of the SRRA code has resulted In a number of conservative assumptions and Inputs being used in applications of the code. It Is therefore recommended that sensitivity calculations be :
performed to ensure that excessive conservatism does not unrealistically Impact the categorization and selection of piping locations to be, inspected." A. -
NMC's application of the methodology on howthe degradation mechanisms In,: .C.
the different sized sub-segments are.to be 'combined.fully.comports with the approved methodology as stated in the last paragraph of Section 3.2.3, 'Piping' .,
Failure Potential", of the NRC SE and in Section 3.2, "Simplified and Detailed Inputr, In the WCAP-1 4572 Supplement for SRRA- .: i "If more than one degradation mechanism is present In a given piping segment, then the limiting input values for each mechanism should be, combined so that a limiting failure probability Is calculated for. risk ranking',.
As indicated on page 84 In Section 3.5.6, .tFailure:Probability Determination", of.. ....- ..
the approved WCAP-14572, combining degradation mechanisms does not Imply adding the failure probabilities for each mechanism.,. Typically,- one degradationr mechanism will dominate the failure probability In the segment by several orders -,,
of magnitude. However, because of uncertaintiesihe engineering team may not: , .;.
know which of the potential degradation mechanisms will dominate: especially If there are sub-segments of different nominal pipe size in the segment.' Multiple .
nominal pipe sizes in a single segment arise due to the establishment, of initial. - . :. .
segment boundaries based on consequence considerations as-detaIled~on:-:d .- ,
page 57 of the approved WCAP-14572. An appropriate.tool must be .used to, . ;:
determine the failure Impact of the potential degradation mechanisms to determine the dominant mechanism-for the segmentL.As noted,, he-SRRA tool;):-- -. .
was used in the calculation of failure. probability estimates at Palisades.,'As: - .-
detailed in the supplement to the.WCAP-1,4572, multiple factors-must be. C-* -,L .7. ..
considered in determining the piping failure.including:
5 .4
REQUEST FOR CLARIFICATION ON THE US-EOF SUB-SEGMENTS INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REOUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE
- 1. degradation mechanisms,
- 2. pre-service construction and inspection history and practice,
- 3. and physical routing and configuration. , -
Table 3.5-1 of the WCAP-14572 and the WCAP-14572 supplement provide guidelines for Items to consider. In section 3.5.4, the estimated failure probability is identified as being dependent on and significantly Influenced by the following four Items: configuration, components, materials/chemistry and loads.
A degradation mechanism's affect may vary based on the lifferent physicaF configurations of the weld(s). Socket-welds are particularly noted as having low resistance to sustained vibration. It Is alsb noted In'this section that Interactions' among the factors are common. Distinction is made in the discussion between component dependent failure modes, which are generally noted as localized within a segment and materials dependeit oroperational dependent - - .
mechanisms, which may be present throughout the'entire segment. - This directly supports the opening paragraphs of sectiol -3.5 of the WCAP-1 4572, which identified that:
"The failure probability of a segment is characterize-dby the failure ' :' :
potential (probability or frequency as appropriate)bof the Worst case situation in each segment (not asingle selected Weld in each segment).'
Consider the following two hypothetical examples based on typical situations experienced by plant engineering teams for SRRA iriput: * ' 2". *... .......
Example 1: SiQnificant Differences in Pipe6'Slzes4and Potential . L : . .
Degradation Mechanisms In this example segment for high temperatureard pressure piping, a six-inch sub-segment extends s6om-e distahce-from a check valve toa -tee;,.
where the flow Is split ito tWo,three-inch sub-segm'ritsThatetach extend:: .I .
to a pump. Because of a-cbncerti for'water hammer.that'has boccurred in Ci'V : -; 3/4> '
this system at other plants, a one-irich-sub-'sgmrerit was alded at the .- . - ,
high-points (near each'pump).of the three-inch 0ipln'g to periodically vent :, .
the system. If the check valve leaked,-then the weld in thd six- inch- . ,, .. .3/4 sub-segment closest to the valve cOUld expedrience therfal-stratification-. :- ' - -.
Although there Is no evidence that the check Valve is.leaking, it-has ' 1. ,
happened In similar plants so a high fatigue Stress rarige and numberof' o. - . .
cycles for stratification Is selected by the team for the simplified SRRAi- :. ," e >`..
Input. Because of the geometric layout of the plping6,a weld in the . -.
three-inch portion would'see the highest water-hahmmer'Loc'ding, :'which the"!
team estimated only had a one-percent-chance of occurring dbe to the corrective actions that had already been implemented. Another weld In the same size piping also had a pre-service Inspection Indication that was 6
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE small enough that a repair was not required per the American Society of Mechanical Engineers (ASME) code. .Because some imbalance of the pump was observed after the one-inch vent was Installed, there. Is a concern for the potential effects of vibration In the three-inch pipe welds, but particularly In the one-Inch pipe socket-welds nearest to the pumps.
All the piping In the segment Is subject to fatigue loading due to normal heat-up and cool-down and periodic pump testing. The consequence is loss of Inventory and, the system disabling leak rate has been conservatively assumed to be two gallons per minute (gpm) for all three pipe sizes In the segment. -:. . . - :
The assumed SRRA large-leak probabilities after 40 years are as follows (the numbers given in-this example are approximations based on expert.
engineering judgement):..
a) 3.3E-05 for the six;-inch pipe with thermal stratification,- ,....
b) 1.5E-05 for the three-Inch pipe with one-flaw, vlbrati6.n.(inputO corrected for size by SRRA Programi and a one-percent chance of a severe water hammer, c) 5.OE-04 o ne), for one-Inch . . .pipe
. . with. vibration :-- (correction factor of, d) 4.OE-02 for one-Inch.pipe withthermal stratification, one-flaw,.
vibration and a one-percent chance of a severe water hammer.
The SRRA probability of 5.OE-04 should be selected by the engineering team for risk ranking because the probability of option d) Is unduly conservative relative to plant and Industry experience.;The SRRA input.;, .-;:,_.
for option d) would also be u'nrelaistic relative lo'assuruming tfie'sanre. .
six-inch stratification loading neif the check-valve i the one-inch line far
- wvay mvii u, varvt g=,,u Iu~,v*u;* UrIl ,I..I "0,,= .! Iti,*,!u.=,,* !u*..QUII II-I
,!¢ . , '......
one-inch branch line. <. ,. . - -, - ;,,;: . . ,
Example 2: Small Differences in Pipe Sizes and Potential *,
Degradation Mechanisms ; -i ' ,", ,- . '
In this example segment for rnoderate temperature and pressure, three i -.
different pipe sizes are also used (nominal.plpe~size of one,-one and a ha-l .1- -.
and two-inch). All the piping in the segment Is subject-to fatigue !oading ,. ;. - ,
due to normal heat-up and coo!-do'wn and relatively high seismic (SSE).
loading for the design-limiting eyent. The consequence is loss of the system function and disabling leak-rate hasbeen conservative!ýYassumed.: - .
to be ten-percent of the flow through the largest of the three pipe sizes in the segment.
- . !_'.*_*i. *_;:,:: ::i**) ! *'*".: /--*-:: *, *.. :....-........,.......-..;.....,....
7
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS.
INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE The assumed SRRA large-leak.p r*babilities after 40 years are asfollows (the numbers given in this example. are approximations'based on expert engineering judgement):
a) 8.9E-05 for the two-Inch pipe with Its *atigue and SSE loading, b) 1.2E-06 for the one-and-a-half inch pipe with its fatigue and SSE loading, .
c) 7.5E-07 for one-inch pipe. with Its fatigue and SSE loading, d) 9.1 E-05 for the two-inch pipe with'the highest fatigue and highest SSE loading Independent of pipe size.'
The SRRA probability of 9.1 E-05 could'be selected by the "engineering team for risk ranking because the probability of.option, d) is not overly' conservative relative to plant and industrytexperienc6 and the SRRA Input would still be realistic relative to the uncertalnties In the actual loading for the different pipe sizes (i.e. the differen6e between the SRRA calculated '.;
probability values of 8.9E-05 and 9.1 E.105 Isno't'statisticallysignificant). " "
It is NMC's position that assessing the uniqueinput pairameters based on the configuration, components, materials/chemistry, and loads by distinct' -.
quantification of all of the potential degradation 106gardsto localized and generalized degradation mechanisms In the entijre segmentfully comp6rts with " . :
. 'I.'
the SE requirement to: ",'
"...ensure that excessive conservatism does not unrealisticAlly impnact th* .*
categorization and selection of piping locItio:ns 'to beIuisnpedted" *', .
The consistency In the items used in deiermiining the critical locatini orlocationss :; "
for inspection is supported by the requirement in WQAP-.14572 Section 3.3. ..
This section Identifies that the selection of Inspectionil.ctionibe based bn'the' d' - * . ,. . .
postulated failure mechanisms and the'loading conditions for the piping segment considering the same four items as In the determination of piping failure, namely:
configuration, components, materials/chemisty and loads.,' i: ( G---.'-' "
Furthermore, the Inspection is not limited to a single degradation mechanism but must consider all possible mechanisms contributing to-the potentialipefiiure' ..
for a given segment at the most likely location of occurrence.. . . .. .
It is NMC's conclusion that the process followed in sub-ividing consequence , - . -:
defined segments fully supports the directive. to apply all'possibie'degradation"' " ' ' -"
mechanisms at a single weld and ensure that tIhiere-s'rno excessive-conseatisr- - _. .
on the piping categorization or selection ofinspection location. '
8
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS, INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45-DAY RESPONSE Requested Item
- 2. Forthe Perduemethod applicationon segments that were subdivided, please provide the definitions used to identify sub-segments. Also please explain how the Perdue input parametersare developed for a segment.
that has been divided into sub-segments, how the results are used to determine the number of locationsfor inspection In the segment, and how your methodology comports with the approved.methodology. :
Response .* .- ". *. .. .
The Perdue Model Is used to aid in the determination of the number of Inspection locations for segments determined to be high safety significant by the plant risk-informed inservice Inspection (RI-ISI) expert panel. Segments were divided into sub-segments (or lots) during the P erdue Model evaluation using the following cases: -.
Case A: There Is an Identified active degradatlon mechanIsm and the segment Is placed In Region Iof WCAP-14572 Figure 3.7-1. :.
For this case, the piping.1n the segment Is the same nominal diameter... ,.
One lot consists of the welds/locations.susceptible to the.degradation mechanism (Region iA).. Each susceptib!e location is Included In the Inspection program ifit is not already part of an augmented inspection program. Welds/locations, which are included In an augmented program,. . .
remain in that program and are ,inspected In accordance with that , .:
program. The other lot consists-of the remainder of the welds in the segment (Region 1B).- These are evaluated with the Perdue Model based.
on SRRA parameters, which exclude the active degradation mechanism.
The total number of Inspections ,for the sgment is the sumof the :* . .
susceptible locations plus the number of Inspections required to achieve a 95% confidence using the Perdue Model .(a minimum of one Jocation is- .. -.
specified even if the Perdue M6del.0shows- .100, confidence_ with no ISI).
This comports with the decription of segments In Region 1 on page 168 of WCAP-14572. , - . .......
Case B: There Is no Identified active de-gradation mechanism and the.
segment has been placed In Region 2 of WCAP-14572 Figuee 3.7-1.
For this case, there are multiple. pipe sizes In.the segMret.,-eThe Perdue, Model Inputs are specific to the pipe material and size.,; The first approach is to combine the most limiting Inputs from each. plpe..size,-use the total number of Welds In the segment, and analyze the segment as one lot.
Alternatively, if this Is so conservative that a 95% confidence level cannot 9
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE be achieved, then eaclh pipe size Is analyzed separately with the appropriate number of welds and the appropriate SRRA results. This divides the segment lrto lots-accordingto pipe size.- The confidence values of each lot are multiplied together to get the confidence for the segment. The resulting confidence level must begreater than or equal to 95% for the Perdue Model evaluation to be acceptable. The total number' of Inspections for the segment is the number of inspections required to.
achieve a 95% confidence using the Perdue Model. A minimum of one location Is specified even If the Perdue Model shows 100% confidence.
with no ISI. This comports with the description of segments in Region 2 on page 168 of WCAP-1 4572 and with the description of dividing a segment into multiple lots*on Oages 174 and 175. - ' " .
Case C: There Is an active de4radafln mechanIsm and'the segment has' 2 been placed in Re-gion I of WCAP-14572 Figure 3.7-1.
For this case, there are multiple pipe sizes In the segment. One lot consists of the welds/locations susceptible-to the degradation mechanism ' ..
(Region 1A). Each susceptibilocation Is 'included In the Inspebtion, program if it is not already part of an augmented Inspection program.
Welds/locations, which are inclIde-din-an idguýented program,: remainlIn that program and are Inspected in accordahce with that programi. 'For the Perdue Model evaluation of the'noh -suseptible veldsfocations (Region I B), the steps followied are the same'as' in Case B above.': The ' ' ' ' '
first approach is to combine themriost limitin'g Inputs from each pipe Size ,."
after removing the active degradatioh 'mechianism,; use the total humber of "
welds minus the number of isiceptible'welds, and analyze-the segment "*' :'
as one lot. Ifthis is too conservytiv-6,then each pipe. size is analyzed .... . ' " ' '" .
separately with the approprlife -number-of Welds.and the appropriate , -'
SRRA results. The conf idenc-evalues of'e a-ii lot'are multipliedtogether :,'
to get the confidence for the segmeh.nt. 'Thesu inon o-fidenceiel' must be greater than or equalto 95% forthe-Perdue Modei' evaluatiorn to- '" ' '
be acceptable. The total nu'mrrberd6f-nspectiohs foirthe segmentis the '. ">" ' '"-,
sum of the susceptible locations Olus'the numberbf inspections tequired to achieve a 95% confidence using the Perdue Model (a minimum of one location is specified even ifthe Perdue Model shows 100% confidence with no ISI). This comports with the descrilption of segments inRegion 1' -:' *"-';'- --
on page 168 of WCAP1 4572 and with the description of dividing a- ' '" '
segment Into multiple lots on pages 174 and 175.
Individual Perdue Model inputs are specific to thepipe6material and si*e.* .
Therefore, segments with multiple sizes must beebvaaIUted in'one of the'three "Z '*' 'J ways discussed. In all three approaches the methbdfbr'evaluating segrients
with the Perdue Model fully comportsiwith'the'apiproved methodology. - .
10 C
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE Requested Item
- 3. If you were to apply the failureprobabilityestimation'andthe Perdue methodology to the entire segment for allsegments, 'asopposed to sub segments, how would the total numbef of inspections requiredin the RI ISI programchange?
Response
NMC and Westinghouse are in concurrence that the approved WCAP-1 4572, methodology In application of failure probabilities and'in the application of the' Perdue methodology to piping segments Was followed by'Palisades. B6th -'
parties agree that the responses prepared for the first two questions support and clarify this position. '
Program specific data were evaluated to approximate how the number of Inspections would change If failure probability estimates for sub-segmentswere :'
evaluated with the most limiting Win-SRRA Inputs for all portions of the segment.
There are 193 segments that consist of multipfe pipediameters* - ' .-
and have some variation In the Input pai'ameters. All of the segments with input:
parameters that vary fall Into one'bf three categoriesý:ý .*-. - ,
- 1. Only variation in Inp*Uts ae pipe size And wall thickness'-:. "
- 2. Variations are all related to pipe and weld gedmretries "
(65 segments) . -~ *
- 3. Variations are based oh ehrgineeng judgment t'garding potential degradation mechanisms (nine segments) ,. .
For segments in the first category; the ohlylvariations inthe inputs are those'-*. .
associated with differences in the actual physical makeup of the pipe (n6minal '. ... . '..
pipe size and thickness to outer diameter ratio). There a&619 input parameters::' " - ' .. .
for each Win-SRRA case run. For these- segments;-thebtheri 6 ;Input '
parameters were the same for all pipe size failuriepriobaibility estimatiohs. The ,'
limiting case for each of the 119 segments in'thls category is-the absolutelimiting .
case for the segment, therefore, there Would be no change to the numberof .
inspections. The Perdue Model Was applied tb'the high safety~signifiCant (HSs) :-..*,s-:'.- ,
",f ',
segments as described in the responseto 'question 2,;exceptir' cases Where It C was not applicable such as socket-welded piping>JThus,ý fodrthls categoty, there" would have been no changes to the number of Inspections.
There are 65 segments incýategory two. All 65 segments include both small bore: '.
(socket-weld) and large bore (butt-weld)piping." All had variations In the' ' -, ' :-.'
Win-SRRA inputs due to pipe size'differences oriweJd geometry diffe'rences.-The small-bore socket welded piping consistently had more limiting Win-SRRA Inputs 11 1 6
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT-45 DAY RESPONSE for DWIThermal Stress and Design Umiting Stress. A sample of four of the segments was reevaluated to run the Win-SRRA code on the larger bore piping with the more limiting Inputs associated with the small. bore portions of the segments. The failure probability for the large bore piping did Increase In every case. However, the original failure estimates generated.for the small bore piping were still the highest overall in each of the four, segments. The failure probabilities used to represent the segments in this category represent the most limiting Inputs associated with those segments. Examples have shown that applying failure estimates for the entire segments as opposed to sub-segments for segments in this category would not have changed the number of Inspections.
As identified on page 178.of WCAP-1.4572, Revision 1-NP-A, the Perdue Model.
should not be used for socket-welded piping,- For the HSS segments In this category, at least a portion of the pipingis-socket-welded.. The SRRA-runs .
associated with the socket-welded piping should not be used for the Perdue Model inputs. For the portions of the segments In this category that are not socket-welded, the SRRA.runs representing the non-socket-weldedportions of the segment were used to determine:the numberof inspections..; In determining the number of Inspections using the Perdue Model:It would be inappropriate to use inputs for the socket-Welded piping. Thus the-appropriate Inputs were used:'.
for the Perdue Model for the segments in this'category and, therefore, there: - .
would be no change to the. number of Inspections.
For segments In the third category, an eValuatiorn.using:the most limiting-..- :
Win-SRRA Inputs was not performed. The decisions.for the Inputs that were used were based on known and studied conditions specific!to each section of the .
pipe. A number of the segments In this category had variations in the flow accelerated corrosion (FAC) inputs for different sub-segments of the same 1 .r - n' .
segment. The inputs selected for FAC tor each of the sub_-segmentsarejin-.*;:,-ý accordance with the rankings developed In the Palisades FAC Program for that portion of the system piping. The fallureestimates generated for-the cases' are : -;
realistic and reflect known-conditions in the piping-..Jn this and similar cases :.
there is actual plant specific data that WaS used to:develop the-Win-SRRA inputs.
Additionally, all nine segments-in the third category ended'Upas lowsafety.,
significant (LSS). If the segments had been divided up and evaluated as; . ..
individual segments, none of the additional segments would have ended up HSS.-. ,
The inputs associated with -each sub-segment were'limiting for that sectionof:the -' ,
pipe. The most limiting failure probabilities were then used to represent the - ., - .....
segment. If the segments were split,. the failure probabilities would be the same . ... ..
or lower than the failure probabilities used for the nine segments and the risk,-,
reduction worth (RRW) for the sub-segments would be the same or lower than the RRW for the nine segmients. Since the nine segments were cateOodzed as - 7-.
LSS, It Is reasonable to assume that the -sub-segments would also be made :LSS.
Because the segments are LSS there are noinspections required as part of th.
RI-ISI program. Thus there.would be no changeln'the numberof Inspections for ... -
12
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE these nine segments. For each:6f the'three categories of segments with multiple sizes, there Is no change to the number of Inspections. NMC would expect no changes to the number of inspections.
The following attachment provides additional Information to further clarify response 3.
SI. .* - . . . .. .
3/4 ýc
- -: ',p5, 3 ,]: .***,;3 = -r -; : 7, .. ;:$)t'-,p~ !; ' 1/4 *.' ; : - .7.,
- " .' ,C :,q ;r ,, r-* - q * *.-,." t *'3/4..
S'.']:
. . . .: ;t -.. : Jr" -" *
- I
- 25 5 ..
- -'-~ ... r. : ***.: . *.( -.. .- " - .; *i
': '-q !! .:i ' A7
] *; ' . . "' :,r I i 7;"," ' " .. 5'-I'
- ,__ " S S . . ' . . .*: . ,. . : * . .: " , , ' :
S" " 'v3'
- ,L ",L* ' r S . i d_.
s'= j 1
S;L ,
55 L5: *. . " ". tI. ."-
13
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAy RESPONSE ATTACHMENT NUCLEAR MANAGEMENT COMPANY; LLC PALISADES NUCLEAR PLANT DOCKET 50-255 ADDITIONAL INFORMATION TO FURTHER CLARIFY RESPONSE 3 14
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE.
Palisades risk-informed inservice Inspection (RI-ISI) program divided the plant piping systems into 799 segments. To determine failure probability estimates, the Westinghouse Structural Reliability And Risk Assessment Model (Win-SRRA) code was used. Since some of the Input parameters for the code reflect the physical characteristics of the pipe (e.g. nominal pipe size), each segment that was made up of more than one pipe diameter required more than one set of Win-SRRA input parameters. There are 193 segments that contain multiple pipe diameters and thus have some variation in the Input parameters. All of the segments with inputs parameters that vary fall Into one of three categories:
- 4. Only variation in Inputs are pipe size and wall thickness (119 segments)
- 5. Variations are all related to pipe and weld geometries (65 segments)
- 6. Variations are based on-engineering judgment regarding potential, degradation mechanisms (nine segments)
CATEGORY 1 Table 3.1 shows the Win-SRRA Input parameters for a segment in category one.
The only parameters listed In the table are those with different Inputs for the sub segments. Inputs not listed In the table are Identical for both sub-segments.
Table 3.1 Category 1 Segment CSW-004 Wln-R*rAIn*put' . '1 Sizes Reason For InptýV*er*fion.
Nominal Pipe Size (inches) 16 24 Physical characteristic of pipe Thickness to O.D. Ratio 0.023 0.016 Physical characteristic of pipe (inches)
Table 3.2 shows the results of the Win-SRRA runs generated for the two sub-segments (one twenty-four-inch and one sixteen-inch) that make up CSW-004. Small leak probabilities are provided because they are used for comparison with experience while large leak probabilities are provided because they are used for risk ranking.
IlýFACs Table 3.2 Segment CSW-004 SRRA Results CSW-004
'Resfift (16-Inch) small leak 4.40E-3 FallurieProoablity 1
WithIS1 1.86E-4 CSW-004 (16-Inch) large leak 4.40E-3 1.86E-4 CSW-004 (24Inch) small leak 4.20E-3 I1.07E-4 CSW.004 (24.Inch) large leak 4.20E-3 1.07E-4 In the above example, the differences In the inputs to develop failure estimates are all specifically related to the physical makeup of the piping. The other 16 input parameters for the segment were the same for both pipe size failure 15 4
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE probability estimations. Applying failure esiimateSfor the entire segments as opposed to sub-segments for segmiehts In this category would not have'changed the number of Inspections.
CATEGORY 2 Table 3.3 lists the Win-SRRA Input-parameters for a segment from category 2.
The only parameters listed in theltable are those with different inputs for the sub-segments. For these cases, all the variations In the inputs are due to pipe size differences or weld geometry differences.
Table 3.3 Category 2 Segment BLD-009 . . .
Wln5RA npt Mpes Reason 1F;r InuWVarlaticg
- Parameters' . . 2-kzct&- nch Nominal Pipe Size (inches) 2 4 " Nominal Pipe Size Thickness to O.D. Ratio 0.092 0.075 . Thickness to O.D. Ratio (inches) _______
Design Umiting Stress 0.26 0.1 Medium (0.26) value recommended for
..........- __ small bore piping.
Table 3.4 below shows the results of the Win-SRRA runs generated for the two sub-segments (one two-inch and ond four-inch)that make up BLD-09: The" table also shows the results of the four-inch'portion of ihe segment evaluated with the most limiting dead weight (DW), thermal Stregs and design limiting stress' inputs. -- .. " . -
Table 3.4 Segment BLD-009 RA o@.mlt -
IL--
WinSRRA Case Results Failu re*Probability Wihu IS wih S BLD-00 2-Inch) small leak -4.5S12-4 I 5.55E-7 BLD-009 (2-Inch) large leak 5.63E-5 I 5.38E-5 BLD-009 (4-inch) small leak - &2SE-5 -3.51 E-7 4-*:
i,.'." i** ?.. :!,'. ..
- BLD-009 4-Inch la leak 2.67E7 1.71 E-9.
The results below are revised. The Inputs for DW& Thermal Stress and Design ULmiting Stress were Increased to match' the Inputs for the 2-nch base.'!,*. - -.- . I, BLD-009R (4-Inch) small leak I . 3.28E-5 -H - - 3.51E-7.-,
BLD-009R 4-inch) large leak I - 5.36E-5 _.
. 5.26 E-5.
The example from category two ,(Table 3.3)is a segmept that consists.of two different pipe diameters. The fourt-inch diareter lpipig-consists of all butt-welds.,.
The two inch piping In the segment Is small bore piping allwelds associated
-nd with Itare socket-welds. Due t'differences in the specific geometries between socket-welds and butt-welds, mor' limiting hputs for DW,-thermal stress and -l design limiting stress were rec~ommended forthe small bore piping: .
The results of applying the most limiting Win-SRRMinputsto each pipe size in. ..... * .
the segment have no impact for this segment.. The. most.1imiting Inputs were applied to the small bore piping originally... Applyng the same, .higheryalus for, ...
DW, thermal stress and design limiting stress to the large bore piping does 16
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE increase the large leak failure robability for that porion of the segment.
However, the original failureprobabilities associated with the two-Inch section are still the highest overall, and would be selected to represent the segment.
There are 65 segments that fitinto category two. All 65 segments Include both small bore (socket-weld) and large bore (butt-weld) piping. The more limiting Win-SRRA inputs were cornsistently applied to the small bore plping. .A sample of four of the segments were reevaluated to run the Win-SRRA code on the larger bore piping with the more limiting Inputs assOciated-with the small bore portions of the segments. The failure probability for the large-bore piping did Increase in every case. However, the original failure estimates generated for the small bore piping were still the highesf oVerall in each of the four segments.; Additional examples from this category are Included below.!-- . : - . .,
ExamDle 1: Cateoorv 2 Se-ment CBA-....f- .--
larSfe' '-Inpt '"Reason F&rI Viiri*VaH4on Nominal Pipe Size (inches) _ _1 4 Physical characteristic of pipe Thickness to O.0. Ratio 0.101 0.027 Physical characteristic of pipe (inches) . _" __._ . .. .
Dead Weight & Thermal 0.11" 005 Medium (0.11) valud0 recommended for Stress Level ,. - 4- malbore piping.
Design Limiting Stress .0.26. , 0.1 Medlum:(0.26) value recommended for
____'-__" ______-. small bore piping.,
VV~ff-SRRA~isiefesufts oad~ie S~F~u ~ '
~ '~J1 ~ 'V WithoutztSI,ý I With ISIJ CBA-001 0l-inch) large leak 2.52E-3 .2.74E-5 CBA-001 (4-Inch large lAk 9.67E-4 1.59E-4 The results below are revised. The Inputs for DW & Thermal Stress andDesign,,
Limiting Stress were increased to match the In for the-2-Inch c"i, 2, ,.
CBA-001 R 4-inch Il leak F 1.30E-3 . -.
116E.5 ...... .. 7 1 Example 2: Category 2 Segment AFW-002-, - . -
WIn-SRRAmIpue 2: C - Sie - .. Reason For Input Variation.
~Pai~mters ~
'~, 2-nch- 3-Inch- 6-inch _____________
Nominal Pipe Size (inches) 12 3 '6'- Physical charactedstic of pipe Thickness to O.D. Ratio 0.092 -0.062 -;4O.W Physical characteristic of pipe -. . -
(inches)
Initial Flaw Conditions 12.6 1*:- 3-Inch and 6-i4nh butt-welds received past "NDE, (X-Ray) exams, 2-nch Socket-welds
- _______ have not. : .fJi Dead Weight & Thermal 0.11. :-- 0.05 -:-i0.05 Medium (0.11) value recommended for' Stress Level . ___,___ . ._. ... small bore ,p;,hd.,-.,
Design Limiting Stress 0.26,... 0.1 9.1 . Medium (0.26),value recommended for,.
"...... imall bWre piping.
r~T i. c.!
17
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS INTHE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE l~rSRRAcaseResuts ~ -',~ -'I Failure,Pr fblity AFW-002 (2-inch) large leak 2.64E-4 . 4.23E-5 AFW-002 (3-inch) large leak 3.99E 2.OOE-7 AFW-002 (6-Inch) large leak 4.31E-7 1.57E-9 The results below are revised. The inputs for DW &Thermal Stress and Design Limiting Stress were Increased to match the Inputs for the 2-Inch case.
AFW-002R (3-inch) lare leak 2.49E-5 2.64E-6 AFW-002R (6-inch)large leak 8.87E-6 8.19E-6 I.
Example 3: Category 2 Segment CCS-021 --
Win-SRRA input~jf~; -' IP Sies esr o r~tVrai Parimeteza~ ~ - ~1-~ich -- ' 10-1nch Nominal Pipe Size (inches) 1 ., 10 Physical characteristic of Pipe C.
Thickness to O.D. Ratio 0.136 .034 - Physical characteristic of Pipe (Inches) . . . . . . - - - . ...
Dead Weight &Thermal 0.11 0.05 Medium (0.11) value recommended for Stress Level " __- __ smafl
&_., bore piping.
Design Limiting Stress 0.26 .. 0.1 Medium (0.26) value recommended for..
I I : *small bore pipingq . , .
Win.RA.. uts ~ ... ... aliu.-;:- . bit-. v .. . . ,. .. ;
... .; ' ,:;::- . ,*i-.,* .: ,. i*
-M IM s CCS-021 1-Inch large leak -2.25E-5 2.21 E-5'.'.t,:)~
CCS-021 (10-Inch) lame leak *i,7.37E-11 2.75E-12 ...- .- . . .
The results below are revised. The Inputs for DW & Thermal Stressand Design j *' . .. 1'.. '"'
Limiting Stress were Increased to match the Inputs for the 24nch case.
CCS-021 R (10-inch) larie leak I 6.95E-6 6.95E-6 The most limiting Inputs for the segments. in category two were always applied to J' the small bore piping. Applying1fallure, probability estimates to the entire-segment," - .... !I for these segments, as opposed to subs.egments Wquld not chalnge the.,mber -
of inspections for the program . -. _-i-_-.- -- '-. , C CATEGORY 3 The last of the three categonres includes-the segments whose Win-SRRAinputs "
varied at different portions of the segmen-ritbased on enginee'ing judgment- --. ...
regarding potential degradation mechanisrs.1There are'only nine segments in':;'- :,,
this category representing approximately one percent-of the entire population'of--'...:.- -. .. ---
segments. Each segment and the Inputs associated with it are discdssed below"'-":.." .
on a case-by-case basis. ------
Three of the segments In this category are main feedwgkter (MFW) segments.- In. ..............
all three cases the Input that varied fr diff'ere:nt potons of the segment were..m."
associated with flow accelerated corrosion (FAC), which Is reflected In the material wastage potential (MWP) Input.
18
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE Tables 3.5 and 3.6 show the Wln-SRRA input parameteis for the three MFW segments. The only parameters listed In the table are ones with different inputs for the sub-segments. Inputs hotlisted in the table are Identical for the multiple sized cases of the same segment.
Table 3.5 Categor 3 Segment MFW-002 - "
Vlh-SRRAlnput '::.~~Pp ie~xReason For Input Variation~
'Parmees., 8-inch - 84nclVt.: ý15-nch '
Nominal Pipe Size 6 8 18 Physical characteristic of pipe (inches) ":_. - ._-___I _. _ _-._" _:_..-_
Thickness to O.D. Ratio 0.065 0.058 0.064 Physical characteristic of pipe (inch es) .. ..............
Material Wastage 0.05 ,0.1 0.1. FAC values are In accordance with known and Potential I - . ,-- _ -,_-,...-I documented FAC values In piping system.., .
TnhI A Input WIn-SijRA (etpnnn, f nmnntn MFWflfl7A
- .. Floe Sizes' enri &AF'.AlflflRA tinniitc nr idnntiriI 1eason'For Input Variation Pamrriders. . -.2l0-nch' 84rh~-5Inch I D0-, _16-inch 15-inch '
Nominal Pipe Size (inches)..
6 8 I10,- jo 16 . 1- . Physlcalcharacterlstic of pipe
. . .. r . .. !. * . : .,*.
Thickness to O.D. 0.042 0.037 0.047 0.055 0.041 0.047 - Physical characteristic of pipe :
Ratio inches) _ *, __;- ,
Material Wastage 0.05 0.05 0.05-.1 0.05 ý:,:0.055 0.1 FAC values are in accor Potential.
Potentia i,! : with known and documented -.
,F-_I_;i. .: -. _ . .-! 1 FAC valuet in piping system.
(There are two different 10-inch pipe classes for these segments:.One is-EB-9 -
and the other is EBD-901. The 1O-Inch(a) Is the EBD-901 portion.) . ,- .-: . .
Palisades MFW system piping is susceptibletoFAG. Piping for thes ystern'is ,
currently in the Palisades FAC Program and the effects of FAC lir MFWppiping;. -- . .. .'.
have been studied at Palisades since 1988.: The inpUtssel6cted for FAC for each of the sub-segments are in accordance with the rankings developed in the Palisades FAC Program for that portion of the system piping. The Inputs are also slightly conservative since all MFW piping was given, at a minimum, a medium (0.05) FAC value. If a high FAC value"&had been input inf6 one sub-segmeni only' because a different sub-segmet (of th*e same siegme4t) had adWhig inpuit- 6 ," .
would work to defeat the purpose.0f having' ia'1sk-informed approach' in this..... ...
case the Inputs are based on known plant specific data thatf Is generated fro a" program whose purpose Is to check and evaluate piping'forFAC. These' realistic '- .... ,
inputs provide valuable risk insights that:are-lost if excessively conservative inputs are used In their place.
19
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE Table 3.7 below shows the Win-SRRA input parameters for two BLD segments.
The segments are nearly Identical segments, one each from the two BLD piping trains. - "
Table 3.7 Category 3 Segments BLD-001 and BLD-002 (inputs are Identical)
- iWln.SRRAlnput.* *v P**
- Sizes- . ReisonForInputVariation *,:
Paaieters ~Nch 14a '4-inch Nominal Pipe Size 1 .4 .... Physical characteristlc of pipe (Inches) "_-*_______"_
Thickness to O.D. Ratio 0.136 -. 0.075.-- Physical characteristic of pipe _
(Inches)
- Dead Weight &Thermal 0.11 .0.17 - Medium (0.1-11value recommended for small bore M
Stress Level "_'-_-____ . piping. "
Design Limiting Stress 026 -0.1 ------ Medium (0.26) value recommended for small bore piping.
Material Wastage 0.001 -0.05.-, FAC values are In accordance with known and.,
Potential - documented FAC values In piping system.
Portions of the Palisades BLD piping aresusceptible.to FAC. Piping for the system is currently in the Palisades' FAC Program 'and the effects of FAC In BLD" piping has been studied since 1988. The inputs selected. for.FAC for each of the sub-segments are in accordance with the'rankings developed in the Palisades_
FAC Program for that portion of the system piping* The fiilureestimm~te- -. -
generated for the cases are realistic and reflect knbwn conditions in the piping.
Using only the worst of the irput valueso-ach:stze-wouldbe overly.-. .- .
conservative and not produce realistic results.:.,-c. .
Table 3.8 lists the Win-SRRA input parameters for segment BLD-008,jThetwo sub-segments for BLD-008 have Inputs that vary for pipe size differences, weld -.,
geometry differences, and thermal'stratification potential differences. -,,
Table 3.8 Category 3 Segment BLD-008,-..--. ..-.
%9r'i.SRRAIq:put1 "1'PIN'SiZIBS- I.
,ReasonFor Input Variationi Pariameter IA . ,Pinnch Nominal Pipe Size A4 -Physical characteristic of pipe ,
(Inches) _ ____ .- _ - : ;.*I . -, .. .
Thickness to O.D. Ratio 0.147 0.075 PhysicalIcharacteristic of ppe .1 -
(inches) _ * .. .. . . ... .. _ _
Dead Weight & Thermal 0.11 0.17- Medium (0.11) value recommended for small bore Stress Level-- .....ipng. . . -. - .
Design Umiting Stress 0.26 '0.1 'Medium (0.26) value recommended for small bore
_____________________________ ___________piping.
Fatigue Stress Range 0.3 0.5 4-inch section has higher value due to Its Interface with the steam generator.
Low Cycle Fatigue 5 10 4-inch section has higher value due to Its Interface Frequency with the steam generator.
Segment BLD-008 Interfaces with the steam generator and has thermal stratification stress potential. The 3A-inch branch line on the segment is not near the generator and has significantly less thermal stratification stress potential.
The inputs for both flow stress level and fatigue cycle frequency account for the 20
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PALISADES NUCLEAR PLANT 45 DAY RESPONSE potential stratification near the genierator for the four-inch section. Applying the same limiting Inputs for both line ýsizes associated with the segment would be unrealistic and overly conservative (similar to example I Inthe response to question 1).
Table 3.9 lists the Win-SRRA input parameters for asegment from the heaters and extraction drain System (HED). !The only parameters listed in the table are the ones with different Inputs for the sub-segments. For these cases, all the variations Inthe Inputs are due to FAG. ' 5 Table 3.9 Category 3 Segment HEDb-004 Wln-SRR Input~ Pipe lzesFleascon For inputVaato 34o 4-Inchr 12 i~-auwi16-Incqh, Nominal Pipe Size 3 .4 .8. 12 16. Physical characteristic of pipe (inches) ___ ___ I___ ___ ______________
Thickness to O.D. Ratio 0.062 0.053 0.037 0.029 0.023 Physical characteristic of pipe (inches) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Material Wastage 0.2 0.1 0.1 0.2 -0.2. FAC valuJes are In accordance with Potential -- known and documented FAC values
________________ _____ _____ ______ - In 1piping system.
Portions of the HIED piping are susceptibl~e to FA-C.-Piping for the system Is ..
currently In the Palisades FAG Program and the effects of FAG in.HED piping'. ..
has been studied since 1988. The Win-SRRA Inp'uts for material Wastage are In .. ,..
line With the predicted component wear rates of the .Palis~a~des FAG PFrogram.
The failure estimates generated for the -casesare realistic and reflect known conditions in the piping. Using onlyt1he worst of the Jnput values for~each size *,. , :..
would be overly conservative and not-produce realistic results foirthe 4-inch and:.,.,, ~ :
8-inch portions of the piping.. - , ~ -,.i.
Table 3.10 shows the variation in the Win-SRRA Inputs betwee 'n.the sub-segments for two pressurize r (PZR) segments?- The'segments are~iearly.
Identical segments; each one Is Isolated from th.e primary -coolantsysteam (P05): .:
by a normally closed power-operated relief valve (PORV).
Table 3.10 Cateaorv 3 Seaments. PZR-01 1 and.PZR-01 2 finouts are Identical)
~Psramters~ ' ýAA-Inch< 4-Inch1/2`&:. -Ž Nominal Pipe Size .- 4 Physical characteristic of pipe T (inches)_______ ._____ __
Thickness to O.D. Ratio 0470.097 Physical characteristic of pipe (Inches) ______ ______ _____________________
Fatigue Stress Range - 0.3 .:0.5 4-Inch section has higher Value due to Its Interlace
____ ____ ____ ____ -- - wlththe PCs.-
Low Cycle Fatigue 5 0.
1~ 4-Inch section has higher value due to Its interface EFreuenc1y £WU VM M0115~L. Comet daiiainrqur ic f4lOTE: DWlThermal Stress a Design Uimiting Stress Inputs were the samne Wo1 beth aegments.1 . --- ~ s cs caseisqu ~from othearezmpes.
-. ~.*
... ... ... .~where: we sed ditfrrnt values for tbe, con sce c&TeR 11._ -.2z . con.servative values!& y..cr tr both in fo thoriginal, thus so change.
21
REQUEST FOR CLARIFICATION ON THE USE OF SUB-SEGMENTS IN THE RISK-INFORMED INSERVICE INSPECTION RELIEF REQUEST PAUSADES NUCLEAR PLANT 45-DAY RESPONSE Similar to segment BLD-008., the four-inch section of the segments Is susceptible to thermal stratification. The four-Inch sections of the segment are separated from the PCS by normally c.lsed valves that have been known to leak. Due to the location on the segments of the WA-inch branch lines, theyare much less susceptible to the thermal stratification. The Inputs reflect the actual piping conditions and are realistic. Using qnly the worst of the Input values for each size would be overly conservative and not produce realistic results.
SUMMARY
For two of the three categories of segments with multiple Win-SRRA Inputs parameters, applying the-failure probability estimates'to the entire segment as pposed o _sub-segment's Would not Increase the number of inspections. For _ -* ommenb segments In the first category,, the inputs todetermine the failure estimates are the same for each pipe size,:-:The only variations in the Inputs are those ...
associated with the actual physical makeup of the pipe. For segments In.
category two, the more limiting Inputs were -cohsistently applied to the small bore - :- . ,,
socket-welded sections df the segments. Numerous examples show that reevaluating the large bore sections of the pipe with the most limiting inputs J. . -. . .
would raise the failure probabilities for those sub-segments. However, In each .
example, the original limiting failure prtbabilitQ prthe small bore piping) . r associated with the segment renained the highiest Value and would still be:
chosen to represent the seg6ment. 1ased on the ev-dence from the examplesI' , -
applying the failure probabiliti,'estimates to the'eWrti-esegr-ient as opposed to" ' - - I sub-segments for those in cateig ory -twowou",ldnot incirease the number; of inspections. - :' ,
As discussed In the responseto question oorne Ot the *bquest for additional information (RAI), applyingthte mpostconservative SRRA inputs for variou pipe sizes in a weld may result in eXcessive conservatism In the SRRA failu,,re probability for that segmentaind the*refre'shoUldinot- be considered. Applytig "
the worst case Inputs associated withany pat-of the segment to allp0rtions ofIF the segment might change the numn ber of ins-pedlors f16r segments in'category three. However, any additional inspections woul.dbe the result of using overly - .
conservative and unrealisticdataand thlrefoie6-are'ihapproriate. The justification for the variation.in the, Inputs for these-segments is sound and well documented. The decisions for the inputs We-rebased on known andistodied :- .
conditions specific to each.section-of the pipe.', I .
Because the segments in this category are lovwsafety significant (L.SS) and the -
most conservative failure probabilities of the sub-segments were used, had the segments in this category been split, the new segments would havd also been .t -:-
LSS and there would havebeenpno change to the-,number-of Inspections. ' . - 'i - -. ,. .
22