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| | number = ML112770176 | | | number = ML112770176 |
| | issue date = 10/03/2011 | | | issue date = 10/03/2011 |
| | title = South Texas Project, Units 1 and 2 - Licensee Handouts from 10/3/11 Meeting STP LOCA Frequency (TAC Nos. ME5358 and ME5359) | | | title = Licensee Handouts from 10/3/11 Meeting STP LOCA Frequency |
| | author name = Mosleh A | | | author name = Mosleh A |
| | author affiliation = South Texas Project Nuclear Operating Co | | | author affiliation = South Texas Project Nuclear Operating Co |
| | addressee name = Singal B K | | | addressee name = Singal B |
| | addressee affiliation = NRC/NRR/DORL/LPLIV | | | addressee affiliation = NRC/NRR/DORL/LPLIV |
| | docket = 05000498, 05000499 | | | docket = 05000498, 05000499 |
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| {{#Wiki_filter:Technical Review of STP LOCA Frequency EtitiMthdl E s ti ma ti on M e th o d o l ogy Ali MoslehWork Performed for South Texas Project Electric Generation StationOct 3, 2011 1 | | {{#Wiki_filter:Technical Review of STP LOCA Frequency E ti ti M Estimation Methodology th d l Ali Mosleh Work Performed for South Texas Project Electric Generation Station Oct 3, 2011 1 |
| Scope of ReviewLOCA Frequency Estimation Model Interpretation and use of NUREG-1829 information Other ke y assum ptions and com putational ste p s used ypppto generate the numerical resultsTwo rounds of review were done, one on an earlier draft (Early August, 2011), and one on the final report (dated Sept 2011) 2 LOCA Frequency Estimation Model Overview Current report has focus ed on estimation of the frequency of LOCAs initiated at or near the location of pipe and nozzle weldsFtkillildLOCAdtifilt F u t ure wor k w ill i nc l u d e LOCA s d ue t o p i pe f a ilures a t other locations and non-pipe related failures in the RCS pressure boundary 3 | | |
| Basic Estimation Model Overview The model for estimating the frequency of a LOCA of a given size is given by the following equations: P (R F)I F (LOCA x)=m iix ix refers to the various break size ranges such as those used in NUREG-1829 to describe the 6 LOCA categories. jx=ix=ik kP (R x F ik)I ikik=n ikik=n ik f ik N i T i 4 Definitions 5 | | Scope of Review y LOCA Frequency Estimation Model y Interpretation and use of NUREG-1829 information y Other keyy assumptions p and computational p steps p used to generate the numerical results y Two rounds of review were done, one on an earlier draft (Early August, 2011), and one on the final report (dated Sept 2011) 2 |
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| | LOCA Frequency Estimation Model Overview y Current report has focused on estimation of the frequency of LOCAs initiated at or near the location of pipe and nozzle welds y Future F t workk will ill include i l d LOCAs LOCA d due tto pipe i failures f il att other locations and non-pipe related failures in the RCS pressure boundary 3 |
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| | Basic Estimation Model Overview y The model for estimating the frequency of a LOCA of a given size is given by the following equations: |
| | F(LOCAx ) = mi ix i |
| | jx = ix = ik P(Rx Fik )Iik k |
| | nik nik ik = = |
| | ik fik N iTi y x refers to the various break size ranges such as those used in NUREG-1829 to describe the 6 LOCA categories. |
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| | Definitions 5 |
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| Definitions 6 | | Definitions 6 |
| Basic Estimation Model Overview Different locations are characterized and assigned rupture frequencies based on 45 combinations of system type, weld type, degradation mechanisms, and pipe size. The estimation process is a "bottom-up" approach building the LOCA estimates by combining various
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| contributing components, failure mechanisms, and conditional probabilities. | | Basic Estimation Model Overview y Different locations are characterized and assigned rupture frequencies based on 45 combinations of system type, weld type, degradation mechanisms, and pipe size. |
| 7 Basic Estimation ModelComments and ObservationsThe general decomposition formula follows known principles of calculus of probabilityThe formula represents the commonly made assumption of constant failure rate model for the selected period in plant life lifeThe formulation enables the consideration of known susceptibilities to the damage mechanisms in quantification of the failure rates and probabilitiesIt allows tailoring the probabilities for component-specific vulnerabilities to degradation mechanisms 8 | | y The estimation process is a bottom-up approach building the LOCA estimates by combining various contributing components, failure mechanisms, and conditional probabilities. |
| Basic Estimation ModelComments and Observations Parameter I ik, determined through a previously developed and peer-reviewed Markov model, provides the ability to account for the effects of integrity management programs on reducing likelihood of catastrophic failuresAs a physical model the decomposition formula views the pipe rupture(LOCA)processasatwostageprocessof(1)stochastic rupture (LOCA) process as a two stage process of (1) stochastic occurrence of degraded functional conditions, and (2) stochastic rupture events given a degraded conditionThis is a reasonable first order approximation of a physical process model. Similar formulations are seen elsewhere in PRA such as Precursor Event methodology and some of the commonly used methods for common cause failure analysis analysis 9 | | 7 |
| Basic Estimation Model Comments and ObservationsA key advantage of the approach is the ability to make use of existing operational dataAssumptions in implementation Various degradations (crack, small leak, leak etc) are lumped together as one homogenous class irrespective of their implied severity This means that the same conditional rupture probability applies to all degraded states. The effects is overestimation for some (e.g., crack) and underestimation for other degraded conditions (e.g., | | |
| | Basic Estimation Model Comments and Observations y The general decomposition formula follows known principles of calculus of probability y The formula represents the commonly made assumption of constant failure rate model for the selected period in plant life y The formulation enables the consideration of known susceptibilities to the damage mechanisms in quantification of the failure rates and probabilities y It allows tailoring the probabilities for component-specific vulnerabilities to degradation mechanisms 8 |
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| | Basic Estimation Model Comments and Observations y Parameter Iik, determined through a previously developed and peer-reviewed Markov model, provides the ability to account for the effects of integrity management programs on reducing likelihood of catastrophic failures y As a physical model the decomposition formula views the pipe rupture (LOCA) process as a two stage process of (1) stochastic occurrence of degraded functional conditions, and (2) stochastic rupture events given a degraded condition y This is a reasonable first order approximation of a physical process model. Similar formulations are seen elsewhere in PRA such as Precursor Event methodology and some of the commonly used methods for common cause failure analysis analysis 9 |
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| | Basic Estimation Model Comments and Observations y A key advantage of the approach is the ability to make use of existing operational data y Assumptions in implementation y Various degradations (crack, small leak, leak etc) are lumped together as one homogenous class irrespective of their implied severity y This means that the same conditional rupture probability applies to all degraded states. The effects is overestimation for some (e.g., crack) and underestimation for other degraded conditions (e.g., |
| | leak) 10 |
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| | Basic Estimation Model Comments and Observations y The contributions of various DMs at a specific piping location are combined linearly to determine the total LOCA frequency distribution (for each weld /location) y This is a first order approximation to a significantly more complex case where synergetic effects of multiple DMs are considered explicitly. However, the state of the art in terms of experimental results and theoretical models for the synergistic effects is quite limited y To some extent the the net effect of synergistic phenomena are accounted for via the use of actual data in the failure frequency estimation estimation stage 11 |
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| | Failure Rate Development Steps y 1.1 Determination of component and weld types y 1.2 Perform data query for failure counts y 1.3 Estimate component exposure y 1.4* Develop component failure rate prior distributions for each damage mechanism (DM) y 1.5* Perform Bayes update for each exposure case (combination of weld count case and DM susceptibility case) y 1.6* Develop mixture distribution to combine results for different exposure hypotheses to yield conditional failure rate distributions given STP specific applicable DMs y 1.7 Calculate total failure rate over all applicable damage mechanisms |
| | * Subject of specific comments on next viewgraph 12 |
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| | Observations on Failure Rate Development Steps y STEP 1.4 Develop component failure rate prior distributions for each damage mechanism (DM) y From earlier work in EPRI RI-ISI, peer reviewed y Very wide lognormal distributions, based on existing pipe failure rates, engineering judgment, and use of data y STEP 1 1.5 5P Perform f B Bayes update d t for f each h exposure case (combination of weld count case and DM susceptibility case) y Standard use of Bayesian updating (mostly with 0 failures), well established and accepted in PRAs y Computations were done with aid of a validated and widely used computer code 13 |
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| | Observations on Failure Rate Development Steps y STEP 1.6 Develop mixture distribution to combine results for different exposure hypotheses to yield conditional failure rate distributions given STP specific applicable DMs y Use of (equally weighted) mixture of distributions to generate a composite distribution for different data assumptions is an accepted (advanced) methodology within the Bayesian framework. |
| | y The report has applied this methodology in a very systematic and rigorous way y The applied Monte Carlo sampling technique and numerical procedures were not subjects of this review y While the process and assumptions are clearly stated (see for example table 3- |
| | : 1) the scope of this review did not include an evaluation of the technical basis for assumptions made in the process of estimating population size for each class (weld, pipe segment, ect,) and in assessing the level of susceptibility of each class to various failure mechanisms 14 |
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| | Conditional Rupture Probability Estimation Methodology y The goal is to develop a set of conditional rupture probabilities (CRPs) vs. break size for each component category y CRPs are estimated by anchoring the the generic total frequency of each of the six LOCA classes on two distinct sources of NUREG-1829 data y Base case analyses of specific PWR components (hot leg, surge line, HPI line for a specific 3-loop PWR) developed by B. Lydell using methodology similar to that used by the current study y Estimates of 9 experts of LOCA frequencies vs. break size for many PWR components for the entire fleet of U.S. PWRs 15 |
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| | Conditional Rupture Mode Probability Model Steps y 2.1 Select components to define conditional rupture probability (CRP) model categories y *2.2 Obtain expert reference LOCA distributions from NUREG-1829 y *2.3 Obtain expert multiplier distributions for 40yr LOCA frequencies from NUREG-1829 y *2.4 Determine 40yr LOCA distributions (product of steps 2.2 and 2.3) for each expert, fit to lognormal y *2.5 Determine geometric mean of expert distributions from Step 2.4 (lognormal) |
| | * Subject of specific comments on next viewgraph 16 |
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| | Observation on CRP Estimation Steps y STEPS 2.2 and 2.3 y Some NUREG-1829 experts had provided asymmetric inputs for lower, middle, and upper values, inconsistent with lognormal distribution characteristics y NUREG-1829 used split lognormal distributions to treat this asymmetry.t TheTh STP approach h fits fit the th asymmetric t i cases to t standard t d d lognormal distribution in part to simplify the procedure y Of the three possible alternatives, this reviewer recommended use of Upper and Mid values to determine the corresponding distribution y preserves the central tendency of the distribution and y keeps the experts upper bound estimate which carries more risk significance 17 |
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| leak) 10 Basic Estimation Model Comments and ObservationsThe contributions of various DMs at a specific piping location are combined linearly to determine the total LOCA frequency distribution (for each weld /location) This is a first order approximation to a significantly more complexcasewheresynergeticeffectsofmultipleDMsarecomplex case where synergetic effects of multiple DMs are considered explicitly. However, the state of the art in terms of experimental results and theoretical models for the synergistic effects is quite limitedTo some extent the the net effect of synergistic phenomena are accounted for via the use of actual data in the failure frequency estimation estimation stage 11 Failure Rate Development Steps 1.1Determination of component and weld types1.2Perform data query for failure counts1.3Estimate component exposure 1.4*Develop component failure rate prior distributions for each damage mechanism (DM) 1.5*Perform Bayes' update for each exposure case (combination of weld count case and DM susceptibility case
| | Observation on CRP Estimation Steps y STEP 2.4 Determine 40yr LOCA distributions (product of steps 2.2 and 2.3) for each expert, fit to lognormal y This is done for each experts estimate prior to aggregation of the result of 9 experts (correct approach among alternatives) y The procedure follows basis probability rules for developing distribution of product of lognormally distributed quantities 18 |
| ) 1.6*Develop mixture distribution to combine results for different exposure hypotheses to yield conditional failure rate distributions given STP specific applicable DMs1.7Calculate total failure rate over all applicable damage mechanism s
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| * Subject of specific comments on next viewgraph 12 Observations on Failure Rate Development Steps STEP 1.4 Develop component failure rate prior distributions for each damage mechanism (DM) From earlier work in EPRI RI-ISI, peer reviewedVery wide lognormal distributions, based on existing pipe failure rates, engineering judgment, and use of dataSTEP15PfB'dtfh STEP 1.5 P er f orm Bayes' up d a t e f or eac h exposure case (combination of weld count case and DM susceptibility case
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| )Standard use of Bayesian updating (mostly with 0 failures), well established and accepted in PRAsComputations were done with aid of a validated and widely used computer code 13 Observations on Failure Rate Development Steps STEP 1.6 Develop mixture distribution to combine results for different exposure hypotheses to yield conditional failure rate distributions given STP specific applicable DMsUse of (equally weighted) mixture of distributions to generate a composite distribution for different data assumptions is an accepted (advanced) methodology within the Bayesian framework. The report has applied this methodology in a very systematic and rigorous wayThe applied Monte Carlo sampling technique and numerical procedures were not subjects of this reviewWhile the process and assumptions are clearly stated (see for example table 3-1) the scope of this review did not include an evaluation of the technical basis for assumptions made in the process of estimating population size for each class (weld, pipe segment, ect,) and in assessing the level of susceptibility of each class to various failure mechanisms 14 Conditional Rupture Probability Estimation MethodologyThe goal is to develop a set of conditional rupture probabilities (CRPs) vs. break size for each component category CRPs are estimated by anchoring the the generic total frequency of each of the six LOCA classes on two distinct sources of NUREG-1829 dataBase case analyses of specific PWR components (hot leg, surge line, HPI line for a specific 3-loop PWR) developed by B. Lydellusing methodology similar to that used by the current study Estimates of 9 experts of LOCA frequencies vs. break size for many PWR components for the entire fleet of U.S. PWRs 15 Conditional Rupture Mode Probability Model Steps 2.1 Select components to define conditional rupture probability (CRP) model categories*2.2 Obtain expert reference LOCA distributions from NUREG-
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| 1829*2.3 Obtain expert multiplier distributions for 40yr LOCA frequencies from NUREG-1829*2.4 Determine 40yr LOCA distributions (product of steps 2.2 and 2.3) for each expert, fit to lognormal*2.5 Determine geometric mean of expert distributions from Step 2.4 (lognormal)* Subject of specific comments on next viewgraph 16 Observation on CRP Estimation StepsSTEPS 2.2 and 2.3 Some NUREG-1829 experts had provided asymmetric inputs for lower, middle, and upper values, inconsistent with lognormal
| | Observation on CRP Estimation Steps y STEP 2.5 Determine geometric mean of expert distributions from Step 2.4 y The report investigated two approaches for forming composite distributions, y Mixture Distribution Method (with equal weight for all experts) y Geometric Mean Method (by taking the geometric means of two parameters of the experts lognormal distributions, medians and range factors) y The Geometric Mean method, which is the approach taken by NUREG-1829 was also adopted by the report y In this reviewers opinion, in general the mixture distribution approach to expert opinion aggregation has a stronger technical basis. However, an equally important factor is the engineering assessment by NUREG-1829 and the STP report of the overall suitability of the results produce by each approach. |
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| distribution characteristics NUREG-1829 used "split lognormal distributions" to treat this tThSTPhfitthtittddasymme t r y. Th e STP approac h fit s the asymme t r i c cases t o s t an d ar d lognormal distribution in part to simplify the procedure Of the three possible alternatives, this reviewer recommended use of Upper and Mid values to determine the corresponding | | Conditional Rupture Mode Probability Model Steps y 2.6a Benchmark Lydell Base Case Analysis for selected components y 2.6 b Determine failure rate distribution for Lydell Base Case analysis in NUREG-1829; fit to lognormal y 2.6c Apply Lydell CRP model from Base Case Analysis y 2 6d D 2.6d Determine t i LOCA frequency f distribution di t ib ti from f L d ll Base Lydell B C Case Analysis A l i y *2.7 Determine mixture distribution of NUREG-1829 GM (from Step 2.5) and Lydell LOCA frequency (from Step 2.8) to obtain Target LOCA frequency Distribution for each CRP category component y *2.8 Apply formulas to calculate CRP distributions to be used as prior distributions for each component assigned to each CRP category y *2.9 For each component in CRP category, perform Bayes update with evidence of failure and rupture counts from service data. |
| | * Subject of specific comments on next viewgraph 20 |
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| distributionpreserves the central tendency of the distribution andkeeps the expert's upper bound estimate which carries more risk significance 17 Observation on CRP Estimation StepsSTEP 2.4 Determine 40yr LOCA distributions (product of steps 2.2 and 2.3) for each expert, fit to lognormalThis is done for each expert's estimate prior to aggregation of theresultof9experts(correctapproachamongalternatives) the result of 9 experts (correct approach among alternatives)
| | Observation on CRP Estimation Steps y STEP 2.7 Determine mixture distribution of NUREG-1829 GM (from Step 2.5) and Lydell LOCA frequency (from Step 2.8) to obtain Target LOCA Frequency distribution for each CRP category component y The report has viewed NUREG-1829 expert opinions and y |
| The procedure follows basis probability rules for developing distribution of product of lognormallydistributed quantities 18 Observation on CRP Estimation StepsSTEP 2.5 Determine geom etric mean of expert distributions from Step 2.4The report investigated two approaches for forming composite distributions, Mixture Distribution Method (with equal weight for all experts)Geometric Mean Method (by taking the geometric means of two parameters of the experts lognormal distributions, medians and range factors)The Geometric Mean method, which is the approach taken by NUREG-1829 was also adopted by the reportIn this reviewer's opinion, in general the mixture distribution approach to expert opinion aggregation has a stronger technical basis. However, an equally important factor is the engineering assessment by NUREG-1829 and the STP report of the overall suitability of the results produce by each approach.
| | Lydells approach pp as two largely g y separate p sources of information on LOCA frequencies. |
| 19 Conditional Rupture Mode Probability Model Steps2.6a Benchmark LydellBase Case Analysis for selected components2.6 b Determine failure rate distribution for LydellBase Case analysis in NUREG-1829; fit to lognormal 2.6c Apply LydellCRP model from Base Case Analysis26dDtiLOCAfditibtifLdll BCAli 2.6d D e t erm i ne LOCA frequency di s t r ib u ti on f rom L y d e ll B ase C ase A na l ys i s*2.7 Determine mixture distribution of NUREG-1829 GM (from Step 2.5) and LydellLOCA frequency (from Step 2.8) to obtain Target LOCA frequency Distribution for each CRP category component*2.8 Apply formulas to calculate CRP distributions to be used as prior distributions for each component assigned to each CRP category*2.9 For each component in CRP category, perform Bayes update with evidence of failure and rupture counts from service data.* Subject of specific comments on next viewgraph 20 Observation on CRP Estimation StepsSTEP 2.7 Determine mixture distribution of NUREG-1829 GM (from Step 2.5) and LydellLOCA frequency (from Step 2.8) to
| | y This reviewer agrees that the overlap of the two sources are less pronounced than the differences in corresponding modeling and quantification approaches y Of possible options for use of these two sources of information, the report has chosen a mixture distribution of GM and Lydell results, following a recommendation form this reviewer. |
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| obtain Target LOCA Frequencydistribution for each CRP category componentThe report has viewed NUREG-1829 expert opinions and L ydell'sa pproach as two lar g el y se parate sources of yppgypinformation on LOCA frequencies. This reviewer agrees that the overlap of the two sources are less pronounced than the differences in corresponding modeling and quantification approachesOf possible options for use of these two sources of information, the report has chosen a mixture distribution of GM and Lydellresults, following a recommendation form this reviewer.
| | Observation on CRP Estimation Steps y STEP 2.8 Apply formulas to calculate CRP distributions to be used as prior distributions for each component assigned to each CRP category y This step is straightforward conceptually, but requires careful numerical (MC) procedures. This review however did not look into the details of computational implementation y STEP 2.9 For each component in CRP category, perform Bayes update with evidence of failure and rupture counts from service data. |
| 21 Observation on CRP Estimation StepsSTEP 2.8 Apply formulas to calculate CRP distributions to be used as prior distributions for each component assigned to each CRP categoryThis step is straightforward conceptually, but requires careful numerical (MC) procedures. This review however did not look into the details of computational implementationSTEP 2.9 For each component in CRP category, perform Bayes update with evidence of failure and rupture counts from service
| | y This step follows standard approach to Bayesian updating (beta prior and binomial likelihood) y Updating is done with marginal distributions (beta) of each of the 6 CRP categories given a failure. The joint distribution of CRPs is a multinomial distribution but separate updating with marginal (beta) distribution for each CRP is a reasonable simplification with no visible impact on results give the low values of CRPs 22 |
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| data.This step follows standard approach to Bayesian updating (beta prior and binomial likelihood) Updating is done with marginal distributions (beta) of each of the 6 CRP categories given a failure. The joint distribution of CRPs is a multinomial distribution but separate updating with marginal (beta) distribution for each CRP is a reasonable simplification with no visible impact on results give the low values of CRPs 22 Summary and ConclusionsComments and suggestion on earlier version have been addressed in the final report. Examples include Addition of a more detailed summary of the methodology and charts explaining the steps Betterexplanationofassumptions Better explanation of assumptionsMore consistent application of probabilistic methods in
| | Summary and Conclusions y Comments and suggestion on earlier version have been addressed in the final report. Examples include y Addition of a more detailed summary of the methodology and charts explaining the steps y Better explanation of assumptions y More consistent application of probabilistic methods in some areas 23 |
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| some areas 23 Summary and ConclusionsThe modeling and parameter estimation approaches are found to be sound, acknowledging a number of common approximations and certain simplifying assumptions, some imposed by the limitations in the state of the artThe report's careful and comprehensive treatment of known sources of uncertainty as well as relatively broad rages assigned to distributions are expected to cover much of the impact of the assumptions and limitations in the state of the art 24}}
| | Summary and Conclusions y The modeling and parameter estimation approaches are found to be sound, acknowledging a number of common approximations and certain simplifying assumptions, some imposed by the limitations in the state of the art y The reports careful and comprehensive treatment of known sources of uncertainty as well as relatively broad rages assigned to distributions are expected to cover much of the impact of the assumptions and limitations in the state of the art 24}} |
Letter Sequence Meeting |
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Administration
- Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting, Meeting
Results
Other: ML111640211, ML111861529, ML111890408, ML111890413, ML112130165, ML112350873, ML112350883, ML112630673, ML112630676, ML112770237, ML112770246, ML112770251, ML113050623, ML113060606, ML113060615, ML113060623, ML113210411, ML113330116
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MONTHYEARML1104105052011-02-10010 February 2011
2/22/11 Notice of Forthcoming Public Meeting with STP Nuclear Operating Co., Units 1 & 2, to Discuss Risk-informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance, Resolution Option Approach
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ML1107700052011-04-0505 April 2011
Summary of Meeting with STP Nuclear Operating Company to Discuss a Risk-informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Option Approach for South Texas, Units 1 and 2
Project stage: Meeting
ML1113302442011-05-16016 May 2011
Notice of Meeting with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 and 2
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ML1114706522011-05-16016 May 2011
Correction 06/02/2011 Notice of Meeting with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1
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ML11157A0102011-06-0202 June 2011
STP Nuclear Operating Company, Licensee Handouts, 6/2/2011 Meeting Risk-Informed GSI-191 Closure Plan for GSI-191 Resolution
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ML1116401602011-06-21021 June 2011
Summary of Meeting with STP Nuclear Operating Company Regarding Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance; Resolution Approach for South Texas, Units 1 and 2 (TAC ME5358-ME5
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ML1116402112011-06-24024 June 2011
Notice of Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 & 2
Project stage: Other
ML1118903912011-07-0606 July 2011
Email Additional Materials for Teleconference on 7/7/11 with STP to Discuss Risk Informed GSI-191
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ML1118904082011-07-0606 July 2011
Licensee Handout Loca Frequencie Approach and Example Application
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ML1118904132011-07-0606 July 2011
Licensee Slide Regarding Questions on LOCA Frequency Analysis and Responses to Comments
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ML1118904202011-07-0606 July 2011
Licensee Slide from 7/7/11 Meeting with STP Nuclear
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ML1118903762011-07-0707 July 2011
Email Licensee Slides for 7/7/11 Teleconference with STP to Discuss Risk Informed GSI-191
Project stage: Meeting
ML1118903802011-07-0707 July 2011
Licensee Slides, LOCA Initiating Event Frequencies and Uncertainties(Draft)
Project stage: Draft Other
ML1118615292011-07-12012 July 2011
Notice of Conference Call with STP Nuclear Operating Company to Discuss Risk-informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 and 2
Project stage: Other
ML1120707292011-07-26026 July 2011
Meeting Notice with South Texas Project, Units 1 and 2 - Licensee Slides Computational Fluid Dynamics Validation Plan
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ML1120707072011-07-26026 July 2011
Meeting Notice with South Texas Project, Units 1 and 2 - Licensee Slide Models and Methods Used for Casa Grande
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ML1121301822011-08-0202 August 2011
Meeting Notice with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 and 2 (TAC ME5358-ME5359
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ML1119500942011-08-0404 August 2011
Summary of Meeting with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 and 2
Project stage: Meeting
ML1121301652011-08-19019 August 2011
7/26/11 - Summary of Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 an
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ML1123508732011-08-22022 August 2011
Models and Methods Used for Casa Grande
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ML1123508832011-08-22022 August 2011
LOCA Initiating Event Frequencies and Uncertainties Status Report
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ML1125101482011-09-15015 September 2011
Notice of Meeting by Conference Call with STP Nuclear Operating Co. to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 and 2
Project stage: Meeting
ML1126306732011-09-20020 September 2011
Email, NRC Staff Questions, Loss-of-Coolant Accident Frequency Analysis, Resolution Approach for Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance.
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ML1126306762011-09-20020 September 2011
NRC Staff Questions, Loss-of-Coolant Accident Frequency Analysis, Resolution Approach for Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance.
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ML1127702372011-09-30030 September 2011
LOCA Frequencies for STP GSI-191( Final)
Project stage: Other
ML1127701702011-10-0303 October 2011
E-mail Licensee Handouts for 10/3/11 Public Meeting
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ML1127701762011-10-0303 October 2011
Licensee Handouts from 10/3/11 Meeting STP LOCA Frequency
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ML1127702032011-10-0303 October 2011
Licensee Slides from 10/3/11 Meeting LOCA Frequencies, Final Results
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ML1127702302011-10-0303 October 2011
E-mail Documents for 10/3/11 Teleconference
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ML1127702462011-10-0303 October 2011
E-mail Questions Associated with LOCA Frequency Analysis
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ML1127702512011-10-0303 October 2011
STP Responses to Questions Associated with LOCA Frequency Analysis
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ML1124114192011-10-0404 October 2011
8/22/11 Summary of Meeting with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 and 2 (TAC M
Project stage: Meeting
ML1127901512011-10-11011 October 2011
Notice of Meeting by Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 &
Project stage: Meeting
ML1127900992011-10-11011 October 2011
Notice of Meeting by Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 an
Project stage: Meeting
ML1130606232011-10-20020 October 2011
Technical Review of STP LOCA Frequency Estimation Methodology
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ML1130506322011-10-26026 October 2011
Licensee Handouts from November 1, 2011 Meeting with STP Nuclear Operating Company on GSI-191
Project stage: Meeting
ML1130506232011-10-26026 October 2011
Alion- Expected Impact of Chemical Effects on GSI-191 Risk Informed Evaluation for South Texas Project
Project stage: Other
ML1130606152011-10-31031 October 2011
LOCA Frequencies for STP Nuclear Operating Company GSI-191
Project stage: Other
ML1128401142011-10-31031 October 2011
10/3/11 Summary of Meeting Via Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas
Project stage: Meeting
ML1129701092011-11-0101 November 2011
Notice of Meeting Via Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance, Resolution Approach for South Texas, Units 1 & 2
Project stage: Meeting
ML1132104112011-11-0101 November 2011
Revised Notice of by Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance,
Project stage: Other
ML1130606062011-11-0202 November 2011
Questions Associated with Loss-of-Coolant Accident (LOCA) Frequency Analysis
Project stage: Other
ML1133301162011-11-29029 November 2011
Email, 11/1/2011 Pre-Licensing Conference Call to Discuss the Topic of Expected Impact of Chemical Effects on GSI-191 Risk-Informed Evaluation, Phenomena Identification and Ranking Table Items (TAC ME5358-ME5359)
Project stage: Other
ML1131201292011-11-29029 November 2011
Summary of 11/1/11 Meeting by Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance,Resolution Approach for South Texas, Un
Project stage: Meeting
ML1133505632011-12-0101 December 2011
Licensee Presentation from 12/1/11 Meeting Via Conference Call to Discuss Risk-Informed GSI-191,Assessment of Debris Accumulation on Pressurized Water Reactor Sump Performance
Project stage: Meeting
ML1131801962011-12-0505 December 2011
Summary of Meeting with STP Nuclear Operating Company Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas Units 1 and 2
Project stage: Meeting
ML1134300872011-12-23023 December 2011
Summary of 12/1/11 Meeting by Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas Un
Project stage: Meeting
2011-05-16
[Table View] |
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Category:Meeting Briefing Package/Handouts
MONTHYEARML24080A1292024-03-25025 March 2024
March 25, 2024, Pre-Submittal Meeting for STP QA Plan Change
ML22243A1312022-08-31031 August 2022
STP Nuclear Operating Company August 31, 2022 Presentation - Pre-Submittal Meeting for Updated Main Steam Line Break and Locked Rotor Dose Consequence Analysis to Address Extended Cooldown Timelines
ML22214A0972022-08-0202 August 2022
Presentation by South Texas Project
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Presentation - 7-26-21 Meeting with STPNOC Proposed South Texas Project Moderator Temperature Coefficient TS Change
ML20125A3362020-05-0404 May 2020
STP Presubmittal Meeting Exigent Accumulator LAR 2020-05-05 Presentation L-2020-LRM-0039
ML19326A0072019-11-22022 November 2019
Pre-Application Public Meeting for Proposed License Amendment Request to Revise the STPEGS Emergency Plan - December 3, 2019
ML16356A0612016-12-21021 December 2016
12/21/2016 South Texas Project Aluminum Bronze Aging Management Request for Additional Information
ML16264A3632016-09-20020 September 2016
Pre-Application Public Meeting for Proposed License Amendment Request to Revise the STPEGS Emergency Plan Staff Augmentation Times
ML16210A0442016-07-28028 July 2016
STP Nuclear Operating Company Handouts for July 28, 2016 Public Meeting on GSI-191
ML16172A0192016-07-25025 July 2016
STP Aluminum Bronze Selective Leaching Public Meeting - June 21, 2016
ML16202A4872016-07-21021 July 2016
07/21/2016 Talking Points, Supplemental Information for South Texas Project and NRC Public Meeting
ML16111A0272016-04-18018 April 2016
STP Nuclear Operating Company Slideshow for Public Meeting on April 21, 2016 for GSI-191 Resolution (CAC No. MF2400-01)
ML16062A3042016-03-0202 March 2016
TS 5.3.2 LAR Pre-Submittal Meeting Presentation - March 2, 2016
ML16033A0042016-01-19019 January 2016
Applicant's Slides for STP Meeting on Aluminum Bronze Aging Management
ML15274A5992015-10-0101 October 2015
10-01-15 Public Phone Call
ML15271A3042015-09-28028 September 2015
Public Phone Call Meeting Description of Supplement 2 to STPNOC Risk-Informed Licensing Application to Address GSI-191 and Respond to GL-2004-02
ML15111A0582015-04-15015 April 2015
Licensee Handouts (2 of 2) for 4/22/2015 Public Meeting Possible Roverd Section on Fixed Filtration (TAC Nos. MF2400-MF2409)
ML15111A0562015-04-15015 April 2015
Licensee Handouts (1 of 2) for 4/22/2015 Public Meeting Revised Roverd Section on Large Early Release Frequency Change for Large Break Loss-of-Coolant Accident(Tac Nos. MF2400-MF2409)
ML15056A3862015-02-25025 February 2015
NRC Slides for February 25, 2015 Public Meeting with STPNOC Concerning GSI-191
ML15049A4882015-02-18018 February 2015
Slides for February 25, 2015 Public Meeting
ML15034A1512015-02-0505 February 2015
Integrated Leak Rate Test (ILRT) from 10 Years to 15 Years. NRC Public Meeting Slides - ILRT License Amendment
ML15034A1142015-02-0404 February 2015
STP Risk- Informed Approach to GSI - 191 Roverd 2015 Meeting Blue 1 29 15
ML14192A9842014-08-0404 August 2014
Summary of Pre-Licensing Meeting with STP Nuclear Operating Company to Discuss Future License Amendment Request to Revise TS 6.9.1.6.b.9 to the Leading Edge Flow Meter Technology for Feedwater Flow Measurement
ML14120A0112014-04-29029 April 2014
4/29/2014 - South Texas Project Regulatory Approach for Risk-Informed Pilot Submittal Presentation Relating to 10 CFR 50.46c
ML13352A1422013-12-16016 December 2013
GSI-191 Licensing Submittal Comparison of Changes Between Rev 1 and Rev 2
ML13352A1242013-12-16016 December 2013
NRC Staff Slides South Texas Project Risk-Informed Generic Safety Issue - 191, December 16, 2013
ML13316B9052013-11-13013 November 2013
Albrz Testing Update for NRR Final
ML13150A2162013-05-23023 May 2013
Licensee Slides for 5/23/13 Public Meeting Regarding GSI-191
ML13140A2562013-05-20020 May 2013
Licensee Slides for 5/23/13 Meeting - STP Pilot Submittal for Risk Informed Approach to Resolving GSI-191
ML13023A3342013-02-25025 February 2013
1/15/2013 Summary of Public Meetings Conducted to Discuss Draft Supplemental Environmental Impact Statement Related to Review of South Texas Project, Units 1 & 2, License Renewal Application
ML13051A8552013-02-20020 February 2013
Licensee Slides for 3/5/13 Pre-Application Meeting for Proposed Licensing Action to Revise the Fire Protection Program at STP
ML13029A4972013-01-15015 January 2013
Slides - Preliminary Site-Specific Results of the Environmental Review for South Texas Project License Renewal
ML12297A3312012-11-27027 November 2012
Summary of Prelicensing Meeting with STP Nuclear Operating Company to Discuss Proposed Amendment for Approval of Revised Fire Protection Program Related to Alternate Shutdown Capability for South Texas, Units 1 and 2
ML12264A3202012-10-11011 October 2012
Meeting Handout for 10/11/12 Pre-licensing Meeting License Amendment Request to Revise the Fire Protection Program
ML12145A4382012-05-18018 May 2012
Licensee Handout on Calibration and Benchmarking of Single and Two-Phase Jet Cfd Models
ML1209004042012-03-30030 March 2012
3-27-2012 - STP Public Meeting Handout from Nuclear Innovation North America, LLC on Fukushima Lessons Learned for South Texas Project Units 3 and 4
ML1205405572012-02-22022 February 2012
Licensee Slides for 03/1/12 Meeting with STP Nuclear Operating Company Meeting to Discuss GSI-191
ML1205405702012-02-22022 February 2012
Uncertainty Modeling of LOCA Frequencies and Break Size Distributions for the STP GSI-191 Resolution
ML1205407582012-02-22022 February 2012
STP Summary of January Meeting
ML1204400652012-02-0909 February 2012
Licensee Slides for 2/9/12 Meeting Regarding GSI-191
ML1133505632011-12-0101 December 2011
Licensee Presentation from 12/1/11 Meeting Via Conference Call to Discuss Risk-Informed GSI-191,Assessment of Debris Accumulation on Pressurized Water Reactor Sump Performance
ML1130506322011-10-26026 October 2011
Licensee Handouts from November 1, 2011 Meeting with STP Nuclear Operating Company on GSI-191
ML1127701762011-10-0303 October 2011
Licensee Handouts from 10/3/11 Meeting STP LOCA Frequency
ML1127702032011-10-0303 October 2011
Licensee Slides from 10/3/11 Meeting LOCA Frequencies, Final Results
ML1123508732011-08-22022 August 2011
Models and Methods Used for Casa Grande
ML1123508832011-08-22022 August 2011
LOCA Initiating Event Frequencies and Uncertainties Status Report
ML1120707072011-07-26026 July 2011
Meeting Notice with South Texas Project, Units 1 and 2 - Licensee Slide Models and Methods Used for Casa Grande
ML1120707292011-07-26026 July 2011
Meeting Notice with South Texas Project, Units 1 and 2 - Licensee Slides Computational Fluid Dynamics Validation Plan
ML1118903802011-07-0707 July 2011
Licensee Slides, LOCA Initiating Event Frequencies and Uncertainties(Draft)
2024-03-25
[Table view]
Category:Slides and Viewgraphs
MONTHYEARML24080A1292024-03-25025 March 2024
March 25, 2024, Pre-Submittal Meeting for STP QA Plan Change
ML22243A1312022-08-31031 August 2022
STP Nuclear Operating Company August 31, 2022 Presentation - Pre-Submittal Meeting for Updated Main Steam Line Break and Locked Rotor Dose Consequence Analysis to Address Extended Cooldown Timelines
ML22214A0972022-08-0202 August 2022
Presentation by South Texas Project
ML22153A2942022-06-17017 June 2022
richardsd-hv-th28
ML21203A2702021-07-26026 July 2021
Presentation - 7-26-21 Meeting with STPNOC Proposed South Texas Project Moderator Temperature Coefficient TS Change
ML20248H5322020-09-0404 September 2020
STP Nuclear Operating Company September 14, 2020, Presentation - Pre-Submittal Meeting for Proposed South Texas Project Moderator Temperature Coefficient Surveillance Requirement Technical Specification Change
ML20125A3362020-05-0404 May 2020
STP Presubmittal Meeting Exigent Accumulator LAR 2020-05-05 Presentation L-2020-LRM-0039
ML20034E8192020-02-0606 February 2020
Pre-Application Public Meeting for Proposed License Amendment Request to Revise the STPEGS Emergency Plan
ML19095A6562019-04-0404 April 2019
NRR E-mail Capture - (External_Sender) Handout for 4/10/19 Meeting to Discuss a Proposed Request for South Texas Project, Units 1 and 2, Regarding Repair of Piping Using Carbon Fiber Repair Methods
ML17004A0292017-01-0404 January 2017
Slides for January 4, 2017, Public Meeting on South Texas Project's Resposne to Aluminum Bronze Aging Management Request for Additional Information
ML16356A0612016-12-21021 December 2016
12/21/2016 South Texas Project Aluminum Bronze Aging Management Request for Additional Information
ML16350A3272016-11-17017 November 2016
Transcript of Advisory Committee on Reactor Safeguards Plant License Renewal Subcommittee Meeting - November 17, 2016
ML16264A3632016-09-20020 September 2016
Pre-Application Public Meeting for Proposed License Amendment Request to Revise the STPEGS Emergency Plan Staff Augmentation Times
ML16172A0192016-07-25025 July 2016
STP Aluminum Bronze Selective Leaching Public Meeting - June 21, 2016
ML16188A3682016-07-0606 July 2016
Audit Presentation - Westinghouse Methodology for South Texas Unit 1 LAR: Operation with 56 Control Rods
ML16062A3042016-03-0202 March 2016
TS 5.3.2 LAR Pre-Submittal Meeting Presentation - March 2, 2016
ML16033A0042016-01-19019 January 2016
Applicant's Slides for STP Meeting on Aluminum Bronze Aging Management
ML15334A3972015-11-30030 November 2015
TS 5 3 2 Emergency LAR Pre-Submittal Meeting Presentation
ML15274A5992015-10-0101 October 2015
10-01-15 Public Phone Call
ML15034A1512015-02-0505 February 2015
Integrated Leak Rate Test (ILRT) from 10 Years to 15 Years. NRC Public Meeting Slides - ILRT License Amendment
ML15034A1142015-02-0404 February 2015
STP Risk- Informed Approach to GSI - 191 Roverd 2015 Meeting Blue 1 29 15
ML14192A9842014-08-0404 August 2014
Summary of Pre-Licensing Meeting with STP Nuclear Operating Company to Discuss Future License Amendment Request to Revise TS 6.9.1.6.b.9 to the Leading Edge Flow Meter Technology for Feedwater Flow Measurement
ML14149A0892014-05-21021 May 2014
NRR E-mail Capture - STP-GSI-191 Presentation
ML14120A0112014-04-29029 April 2014
4/29/2014 - South Texas Project Regulatory Approach for Risk-Informed Pilot Submittal Presentation Relating to 10 CFR 50.46c
ML13352A1422013-12-16016 December 2013
GSI-191 Licensing Submittal Comparison of Changes Between Rev 1 and Rev 2
ML13352A1242013-12-16016 December 2013
NRC Staff Slides South Texas Project Risk-Informed Generic Safety Issue - 191, December 16, 2013
ML13316B9052013-11-13013 November 2013
Albrz Testing Update for NRR Final
ML13150A2162013-05-23023 May 2013
Licensee Slides for 5/23/13 Public Meeting Regarding GSI-191
ML13140A2562013-05-20020 May 2013
Licensee Slides for 5/23/13 Meeting - STP Pilot Submittal for Risk Informed Approach to Resolving GSI-191
ML13023A3342013-02-25025 February 2013
1/15/2013 Summary of Public Meetings Conducted to Discuss Draft Supplemental Environmental Impact Statement Related to Review of South Texas Project, Units 1 & 2, License Renewal Application
ML13051A8552013-02-20020 February 2013
Licensee Slides for 3/5/13 Pre-Application Meeting for Proposed Licensing Action to Revise the Fire Protection Program at STP
ML13029A4972013-01-15015 January 2013
Slides - Preliminary Site-Specific Results of the Environmental Review for South Texas Project License Renewal
ML12297A3312012-11-27027 November 2012
Summary of Prelicensing Meeting with STP Nuclear Operating Company to Discuss Proposed Amendment for Approval of Revised Fire Protection Program Related to Alternate Shutdown Capability for South Texas, Units 1 and 2
ML12264A3202012-10-11011 October 2012
Meeting Handout for 10/11/12 Pre-licensing Meeting License Amendment Request to Revise the Fire Protection Program
ML1209004042012-03-30030 March 2012
3-27-2012 - STP Public Meeting Handout from Nuclear Innovation North America, LLC on Fukushima Lessons Learned for South Texas Project Units 3 and 4
ML1204400652012-02-0909 February 2012
Licensee Slides for 2/9/12 Meeting Regarding GSI-191
ML1133505632011-12-0101 December 2011
Licensee Presentation from 12/1/11 Meeting Via Conference Call to Discuss Risk-Informed GSI-191,Assessment of Debris Accumulation on Pressurized Water Reactor Sump Performance
ML1130506322011-10-26026 October 2011
Licensee Handouts from November 1, 2011 Meeting with STP Nuclear Operating Company on GSI-191
ML1127702032011-10-0303 October 2011
Licensee Slides from 10/3/11 Meeting LOCA Frequencies, Final Results
ML1127701762011-10-0303 October 2011
Licensee Handouts from 10/3/11 Meeting STP LOCA Frequency
ML1123508732011-08-22022 August 2011
Models and Methods Used for Casa Grande
ML1123508832011-08-22022 August 2011
LOCA Initiating Event Frequencies and Uncertainties Status Report
ML1120707072011-07-26026 July 2011
Meeting Notice with South Texas Project, Units 1 and 2 - Licensee Slide Models and Methods Used for Casa Grande
ML1120707292011-07-26026 July 2011
Meeting Notice with South Texas Project, Units 1 and 2 - Licensee Slides Computational Fluid Dynamics Validation Plan
ML1118903802011-07-0707 July 2011
Licensee Slides, LOCA Initiating Event Frequencies and Uncertainties(Draft)
ML1118904202011-07-0606 July 2011
Licensee Slide from 7/7/11 Meeting with STP Nuclear
ML11157A0102011-06-0202 June 2011
STP Nuclear Operating Company, Licensee Handouts, 6/2/2011 Meeting Risk-Informed GSI-191 Closure Plan for GSI-191 Resolution
ML1114501952011-05-24024 May 2011
Summary of Meeting with South Texas Project Electric Generating Station 2010 Performance
ML1105503952011-02-22022 February 2011
Licensee Slides from 2/22/11 Public Meeting with STP Nuclear Operating Company
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1/27/11 Presentation on Risk-Informed GSI-191 Project Overview
2024-03-25
[Table view] |
Text
Technical Review of STP LOCA Frequency E ti ti M Estimation Methodology th d l Ali Mosleh Work Performed for South Texas Project Electric Generation Station Oct 3, 2011 1
Scope of Review y LOCA Frequency Estimation Model y Interpretation and use of NUREG-1829 information y Other keyy assumptions p and computational p steps p used to generate the numerical results y Two rounds of review were done, one on an earlier draft (Early August, 2011), and one on the final report (dated Sept 2011) 2
LOCA Frequency Estimation Model Overview y Current report has focused on estimation of the frequency of LOCAs initiated at or near the location of pipe and nozzle welds y Future F t workk will ill include i l d LOCAs LOCA d due tto pipe i failures f il att other locations and non-pipe related failures in the RCS pressure boundary 3
Basic Estimation Model Overview y The model for estimating the frequency of a LOCA of a given size is given by the following equations:
F(LOCAx ) = mi ix i
jx = ix = ik P(Rx Fik )Iik k
nik nik ik = =
ik fik N iTi y x refers to the various break size ranges such as those used in NUREG-1829 to describe the 6 LOCA categories.
4
Definitions 5
Definitions 6
Basic Estimation Model Overview y Different locations are characterized and assigned rupture frequencies based on 45 combinations of system type, weld type, degradation mechanisms, and pipe size.
y The estimation process is a bottom-up approach building the LOCA estimates by combining various contributing components, failure mechanisms, and conditional probabilities.
7
Basic Estimation Model Comments and Observations y The general decomposition formula follows known principles of calculus of probability y The formula represents the commonly made assumption of constant failure rate model for the selected period in plant life y The formulation enables the consideration of known susceptibilities to the damage mechanisms in quantification of the failure rates and probabilities y It allows tailoring the probabilities for component-specific vulnerabilities to degradation mechanisms 8
Basic Estimation Model Comments and Observations y Parameter Iik, determined through a previously developed and peer-reviewed Markov model, provides the ability to account for the effects of integrity management programs on reducing likelihood of catastrophic failures y As a physical model the decomposition formula views the pipe rupture (LOCA) process as a two stage process of (1) stochastic occurrence of degraded functional conditions, and (2) stochastic rupture events given a degraded condition y This is a reasonable first order approximation of a physical process model. Similar formulations are seen elsewhere in PRA such as Precursor Event methodology and some of the commonly used methods for common cause failure analysis analysis 9
Basic Estimation Model Comments and Observations y A key advantage of the approach is the ability to make use of existing operational data y Assumptions in implementation y Various degradations (crack, small leak, leak etc) are lumped together as one homogenous class irrespective of their implied severity y This means that the same conditional rupture probability applies to all degraded states. The effects is overestimation for some (e.g., crack) and underestimation for other degraded conditions (e.g.,
leak) 10
Basic Estimation Model Comments and Observations y The contributions of various DMs at a specific piping location are combined linearly to determine the total LOCA frequency distribution (for each weld /location) y This is a first order approximation to a significantly more complex case where synergetic effects of multiple DMs are considered explicitly. However, the state of the art in terms of experimental results and theoretical models for the synergistic effects is quite limited y To some extent the the net effect of synergistic phenomena are accounted for via the use of actual data in the failure frequency estimation estimation stage 11
Failure Rate Development Steps y 1.1 Determination of component and weld types y 1.2 Perform data query for failure counts y 1.3 Estimate component exposure y 1.4* Develop component failure rate prior distributions for each damage mechanism (DM) y 1.5* Perform Bayes update for each exposure case (combination of weld count case and DM susceptibility case) y 1.6* Develop mixture distribution to combine results for different exposure hypotheses to yield conditional failure rate distributions given STP specific applicable DMs y 1.7 Calculate total failure rate over all applicable damage mechanisms
- Subject of specific comments on next viewgraph 12
Observations on Failure Rate Development Steps y STEP 1.4 Develop component failure rate prior distributions for each damage mechanism (DM) y From earlier work in EPRI RI-ISI, peer reviewed y Very wide lognormal distributions, based on existing pipe failure rates, engineering judgment, and use of data y STEP 1 1.5 5P Perform f B Bayes update d t for f each h exposure case (combination of weld count case and DM susceptibility case) y Standard use of Bayesian updating (mostly with 0 failures), well established and accepted in PRAs y Computations were done with aid of a validated and widely used computer code 13
Observations on Failure Rate Development Steps y STEP 1.6 Develop mixture distribution to combine results for different exposure hypotheses to yield conditional failure rate distributions given STP specific applicable DMs y Use of (equally weighted) mixture of distributions to generate a composite distribution for different data assumptions is an accepted (advanced) methodology within the Bayesian framework.
y The report has applied this methodology in a very systematic and rigorous way y The applied Monte Carlo sampling technique and numerical procedures were not subjects of this review y While the process and assumptions are clearly stated (see for example table 3-
- 1) the scope of this review did not include an evaluation of the technical basis for assumptions made in the process of estimating population size for each class (weld, pipe segment, ect,) and in assessing the level of susceptibility of each class to various failure mechanisms 14
Conditional Rupture Probability Estimation Methodology y The goal is to develop a set of conditional rupture probabilities (CRPs) vs. break size for each component category y CRPs are estimated by anchoring the the generic total frequency of each of the six LOCA classes on two distinct sources of NUREG-1829 data y Base case analyses of specific PWR components (hot leg, surge line, HPI line for a specific 3-loop PWR) developed by B. Lydell using methodology similar to that used by the current study y Estimates of 9 experts of LOCA frequencies vs. break size for many PWR components for the entire fleet of U.S. PWRs 15
Conditional Rupture Mode Probability Model Steps y 2.1 Select components to define conditional rupture probability (CRP) model categories y *2.2 Obtain expert reference LOCA distributions from NUREG-1829 y *2.3 Obtain expert multiplier distributions for 40yr LOCA frequencies from NUREG-1829 y *2.4 Determine 40yr LOCA distributions (product of steps 2.2 and 2.3) for each expert, fit to lognormal y *2.5 Determine geometric mean of expert distributions from Step 2.4 (lognormal)
- Subject of specific comments on next viewgraph 16
Observation on CRP Estimation Steps y STEPS 2.2 and 2.3 y Some NUREG-1829 experts had provided asymmetric inputs for lower, middle, and upper values, inconsistent with lognormal distribution characteristics y NUREG-1829 used split lognormal distributions to treat this asymmetry.t TheTh STP approach h fits fit the th asymmetric t i cases to t standard t d d lognormal distribution in part to simplify the procedure y Of the three possible alternatives, this reviewer recommended use of Upper and Mid values to determine the corresponding distribution y preserves the central tendency of the distribution and y keeps the experts upper bound estimate which carries more risk significance 17
Observation on CRP Estimation Steps y STEP 2.4 Determine 40yr LOCA distributions (product of steps 2.2 and 2.3) for each expert, fit to lognormal y This is done for each experts estimate prior to aggregation of the result of 9 experts (correct approach among alternatives) y The procedure follows basis probability rules for developing distribution of product of lognormally distributed quantities 18
Observation on CRP Estimation Steps y STEP 2.5 Determine geometric mean of expert distributions from Step 2.4 y The report investigated two approaches for forming composite distributions, y Mixture Distribution Method (with equal weight for all experts) y Geometric Mean Method (by taking the geometric means of two parameters of the experts lognormal distributions, medians and range factors) y The Geometric Mean method, which is the approach taken by NUREG-1829 was also adopted by the report y In this reviewers opinion, in general the mixture distribution approach to expert opinion aggregation has a stronger technical basis. However, an equally important factor is the engineering assessment by NUREG-1829 and the STP report of the overall suitability of the results produce by each approach.
19
Conditional Rupture Mode Probability Model Steps y 2.6a Benchmark Lydell Base Case Analysis for selected components y 2.6 b Determine failure rate distribution for Lydell Base Case analysis in NUREG-1829; fit to lognormal y 2.6c Apply Lydell CRP model from Base Case Analysis y 2 6d D 2.6d Determine t i LOCA frequency f distribution di t ib ti from f L d ll Base Lydell B C Case Analysis A l i y *2.7 Determine mixture distribution of NUREG-1829 GM (from Step 2.5) and Lydell LOCA frequency (from Step 2.8) to obtain Target LOCA frequency Distribution for each CRP category component y *2.8 Apply formulas to calculate CRP distributions to be used as prior distributions for each component assigned to each CRP category y *2.9 For each component in CRP category, perform Bayes update with evidence of failure and rupture counts from service data.
- Subject of specific comments on next viewgraph 20
Observation on CRP Estimation Steps y STEP 2.7 Determine mixture distribution of NUREG-1829 GM (from Step 2.5) and Lydell LOCA frequency (from Step 2.8) to obtain Target LOCA Frequency distribution for each CRP category component y The report has viewed NUREG-1829 expert opinions and y
Lydells approach pp as two largely g y separate p sources of information on LOCA frequencies.
y This reviewer agrees that the overlap of the two sources are less pronounced than the differences in corresponding modeling and quantification approaches y Of possible options for use of these two sources of information, the report has chosen a mixture distribution of GM and Lydell results, following a recommendation form this reviewer.
21
Observation on CRP Estimation Steps y STEP 2.8 Apply formulas to calculate CRP distributions to be used as prior distributions for each component assigned to each CRP category y This step is straightforward conceptually, but requires careful numerical (MC) procedures. This review however did not look into the details of computational implementation y STEP 2.9 For each component in CRP category, perform Bayes update with evidence of failure and rupture counts from service data.
y This step follows standard approach to Bayesian updating (beta prior and binomial likelihood) y Updating is done with marginal distributions (beta) of each of the 6 CRP categories given a failure. The joint distribution of CRPs is a multinomial distribution but separate updating with marginal (beta) distribution for each CRP is a reasonable simplification with no visible impact on results give the low values of CRPs 22
Summary and Conclusions y Comments and suggestion on earlier version have been addressed in the final report. Examples include y Addition of a more detailed summary of the methodology and charts explaining the steps y Better explanation of assumptions y More consistent application of probabilistic methods in some areas 23
Summary and Conclusions y The modeling and parameter estimation approaches are found to be sound, acknowledging a number of common approximations and certain simplifying assumptions, some imposed by the limitations in the state of the art y The reports careful and comprehensive treatment of known sources of uncertainty as well as relatively broad rages assigned to distributions are expected to cover much of the impact of the assumptions and limitations in the state of the art 24
