ML13150A216
| ML13150A216 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 05/23/2013 |
| From: | South Texas |
| To: | Plant Licensing Branch IV |
| Singal B | |
| References | |
| TAC MF0613, TAC MF0614 | |
| Download: ML13150A216 (64) | |
Text
PublicMeetingMay23,2013 1
South Texas Project Units 1 & 2 STP Pilot Submittal for Risk-Informed Approach to Resolving GSI-191
PublicMeetingMay23,2013 2
Attendees for STP Michael Murray Manager, Regulatory Affairs Steve Blossom Manager, GSI-191 Project Rick Grantom Manager, Risk Management Projects Ernie Kee Risk Management Engineering Wes Schulz Engineering Coley Chappell Licensing Ken Taplett Licensing Tim Sande Enercon Bruce Letellier, PhD Alion Jeremy Tejada, PhD University of Texas at Austin Rodolfo Vaghetto Texas A&M University Kerry Howe, PhD University of New Mexico Janet Leavitt, PhD Alion Don Wakefield ABS Consulting Steven Frantz Morgan Lewis Zahra Mohaghegh, PhD University of Illinois at Champaign-Urbana
PublicMeetingMay23,2013 3
Desired outcomes
Overview of the planned revised submittal
Summary of additional information to be submitted
STP responses to NRC items required for completion of staffs acceptance review
Recap of desired outcomes
Questions and comments Agenda
PublicMeetingMay23,2013 4
Clear understanding of:
The structure of the submittal The submittal will address the completeness concern of the staff The level of detail that will be provided in the submittal What will be in the submittal and what will be available to the staff for audit Desired Outcomes
PublicMeetingMay23,2013 5
Attachment to the Cover Letter
Responses to NRC items needed for acceptance review.
Generic risk-informed methodology for resolving GSI-191.
Enclosures 2 and 2-1 through 2-4
STP-specific 10 CFR 50.12 exemption requests for ECCS acceptance criterion 10 CFR 50.46(b)(5), and General Design Criteria 35, 38, and 41.
10 CFR 50.90 licensing amendment request (LAR)
Proposed changes to the STP UFSAR for NRC approval.
Enclosures 4 and 4-1 through 4-3
Volume 1 Project Summary
Volume 2 Probabilistic Risk Assessment
Volume 3 CASA Grande Analysis (summary of engineering analysis)
Structure of Revised Submittal - Outline
PublicMeetingMay23,2013 6
Addresses the required content of a RG 1.174 application using the same section numbering scheme as Regulatory Guide 1.174.
Provides summaries of:
The generic methodology and how the risk metrics associated with the residual risk of GSI-191 are determined.
The plant-specific implementation of the methodology.
The Independent Technical Oversight provided to ensure the quality and validity of the project by performing an in-depth scientific review of the phenomenological models developed and experiments conducted. -1: Volume 1 Project Summary
PublicMeetingMay23,2013 7
This volume contains the documentation for the standard process used by STP risk-informed application analyses.
Describes how PRA insights are used to identify and prioritize CASA Grande inputs.
Discusses how the CASA Grande outputs are used as the inputs to the PRA model.
Describes the quantification of the risk metrics and uncertainties (for changes in risk)
Core Damage Frequency (CDF) and delta-CDF
Large Early Release Frequency (LERF) and delta-LERF -2: Volume 2 PRA
PublicMeetingMay23,2013 8
Volume 3 CASA Grande Analysis is a technical evaluation that provides a high level descriptive summary of the phenomenological portion of the overall risk-informed GSI-191 evaluation
Provides a more detailed summary of supporting engineering analyses (CASA Grande evaluation) including:
Input parameters
Assumptions
Methodology
Analysis
Results
Analysis is based on NRC approved guidance for deterministic methods, e.g. NEI 04-07 SER, with differences identified and explained.
Describes the STP Units 1 & 2 implementation of the generic methodology of the risk-informed approach (Enclosure 1) for addressing the required inputs to the plant-specific PRA model. -3: Volume 3 CASA Grande Analysis
PublicMeetingMay23,2013 9
Questions and Comments
PublicMeetingMay23,2013 10 The following slides address the information items needed for acceptance review of the application as identified by the NRC staff in the April 1, 2013 letter.
STP responses to each item and the associated changes that will be included in the revised submittal are summarized.
STP Responses to Acceptance Review Letter
PublicMeetingMay23,2013 11
- 1.
For each exemption request submitted under 10 CFR 50.12, the application should include a narrative as to why the licensee believes that the special circumstances provided in 10 CFR 50.12(a)(2) is present. The licensee in its application has stated that 10 CFR 50.10(a)(2)(ii) and (iii) apply. There appears to be a typographical error and the NRC staff believes licensee meant to invoke 10 CFR 50.12(a)(2)(ii) and (iii). Please confirm this and provide adequate technical basis in support of applicability of 10 CFR 50.12(a)(2)(ii) and (iii).
Also, please describe in detail how the special circumstances address 10 CFR 50.12(a).
Exemption Requests STP Response:
The revised exemption requests will correct the typographical error and address the required information.
PublicMeetingMay23,2013 12
- 2.
The application describes a departure from the method of evaluation described in the Updated Final Safety Analysis Report (UFSAR) used in establishing the design bases in the plants safety analysis, as defined in 10 CFR 50.59(a)(2) and proposes several draft modifications to the UFSAR. In accordance with 10 CFR 50.59(c)(2)(viii), these modifications would appear to be changes in the design and licensing basis and would require a license amendment in accordance with 10 CFR 50.90. Please explain why an amendment is not proposed to accompany this exemption, with the associated draft no significant hazards consideration. The licensee should clearly state the scope and nature of the change to the design and licensing basis.
License Amendment Request STP Response:
Revised submittal will include a license amendment request (LAR) pursuant to 10 CFR 50.90, with the proposed changes to the UFSAR for NRC approval, and a no significant hazards consideration.
PublicMeetingMay23,2013 13 License Amendment Request - Summary
The proposed change reconstitutes the licensing basis using a risk-informed method:
For the long-term cooling ECCS acceptance criterion 10 CFR 50.46(b)(5),
replaces the current licensing basis that applies a deterministic method for evaluating sump performance that meets the regulatory requirements, but has not been demonstrated to fully resolve GSI-191.
For acceptable design of the ECCS containment emergency sumps and suction strainers in support of the design criteria for ECCS and CSS in recirculation mode following postulated loss-of-coolant accidents as specified in GDC-35, GDC-38 and GDC-41.
The proposed change resolves GSI-191 and is submitted for approval based on a risk-informed approach that meets RG 1.174 key principles.
LAR Regulatory Evaluation discusses the exemption requests that support the proposed change to the UFSAR.
The current licensing basis for ECCS compliance with 10 CFR 50.46, including the accident analyses provided in Chapter 15, and GDC-35, and for CSS compliance with GDC-38 and GDC-41 remain unchanged.
PublicMeetingMay23,2013 14
- 3.
To process the proposed exemption, the NRC staff will need to conduct an environmental review. Please provide the description that will address the special circumstances supporting this review in accordance with 10 CFR 51.41 and 10 CFR 51.45.
Environmental Review STP Response:
For each exemption request, environmental considerations will include information to address the following:
10 CFR 51.41 for compliance with Section 102(2) of National Environmental Policy Act (NEPA), consistent with SRP 19.2 (III.4.2) guidance for RG 1.174 applications.
10 CFR 51.22(b), as referenced in 10 CFR 51.20, and categorical exclusion pursuant to 10 CFR 51.22(c)(9).
No significant hazards considerations address the three standards set forth in 10 CFR 50.92, Issuance of amendment.
PublicMeetingMay23,2013 15
- 4.
Please describe how the proposed change will affect the Technical Specifications (TSs). Please indicate whether changes are needed to the operability requirements for the affected systems and any changes to the existing TS Action Statements that may be needed.
Technical Specifications STP Response:
An evaluation of the effect of the proposed change on the Technical Specifications will be included in the LAR:
Consideration of the categories specified in 10 CFR 50.36(c).
Provides a determination that no changes are needed to operability requirements or existing TS Action Statements based on TS definition of Operable/Operability addressing the required support function provided by the containment sumps and strainers for ECCS and CSS
Conforming changes to the TS Bases (for information only) will be included in the markups submitted with the LAR.
PublicMeetingMay23,2013 16 Questions and Comments
PublicMeetingMay23,2013 17
- 5.
The basis for the proposed change is that the residual risk from the remaining GSI-191 issues (e.g., those not already addressed in a deterministic manner) satisfies the criteria in Regulatory Guide (RG) 1.174, Revision 2, An Approach For Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, May 2011 (ADAMS Accession No. ML100910006). However, the application does not appear to provide sufficient detail for the NRC staff to determine whether the criteria of RG 1.174 have been met. Please describe in detail how the principles of RG 1.174 criteria regarding safety margin, defense-in-depth (DID), and change in risk are met. In particular, please include the following:
Basis for the Proposed Change
PublicMeetingMay23,2013 18 5.a.
Regarding the technical evaluation that supports the risk metrics, the Project Summary (Enclosure 4 to the application) describes numerous areas where the technical evaluation deviates from the approved guidance for addressing GSI-191.
However, the application provides little or no information on how the issues were addressed. Please provide a discussion in sufficient detail to permit NRC staff review of the methods, bases, assumptions, acceptance criteria, and results. If test results are used to develop probability distributions, please describe how these distributions were determined and used in the overall risk evaluation. Please also provide the basis for the acceptance criteria chosen. The NRC staff requires additional information in the following areas:
Basis for the Proposed Change
PublicMeetingMay23,2013 19 NRC Approved GSI-191 Methods Methodology for GSI-191 evaluation has evolved, and NRC accepted methods are documented in various sources:
NEI 04-07 and associated SER Plant-specific audit reports Crystal River, Ft. Calhoun, Watts Bar, etc.
March 2008 guidance reports Public meeting minutes NRC requested more information on the technical areas in the submittal that involve deviations from approved guidance (summarized in Volume 1 Project Summary).
Revised submittal will describe the methods, bases, assumptions, acceptance criteria, and results for each of these areas.
PublicMeetingMay23,2013 20 Topical Area: Debris Generation NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison UsesphericalorhemisphericalZOI Usesphericalorhemispherical ZOI Nodifference 17DZOIforNukon andThermal Wrap 17DZOIforNukon andThermal Wrap Nodifference 28.6DZOIforMicrotherm 28.6DZOIforMicrotherm Nodifference 4DZOIforqualifiedcoatings 4DZOIforqualifiedcoatings Nodifference TruncateZOIatwalls TruncateZOIatwalls Nodifference 4categorysizedistributionfor fiberglassdebrisincludingfines, smallpieces,largepieces,andintact blankets Alion proprietary4categorysize distributionmethodology (consistentwithguidanceinSER appendices)
Alion 4categorysize distributionmethodology previouslyacceptedbyNRCfor deterministicevaluations 100%finesforMicrothermdebris 100%finesforMicrotherm debris Nodifference 100%fines(10m)forqualified coatingsdebris 100%fines(10m)forqualified coatingsdebris Nodifference
PublicMeetingMay23,2013 21 Topical Area: Debris Generation NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison 100%failureforallunqualified coatingsdebris Timedependentandpartial failureofunqualifiedcoatings basedonavailabledata.
Newengineeringmodel documentedinVolume3CASA GrandeAnalysis.
Unqualifiedcoatingsfailas10m particlesifthestrainerisfully coveredoraschipsifafiberbed wouldnotbeformed.
Unqualifiedcoatingsfailinasize distributionbasedoncoating typeandavailabledata.
Similarmethodspreviously acceptedbyNRCfor deterministicevaluations Plantspecificwalkdownsrequiredto determinelatentdebrisquantity STPspecificwalkdownusedto determinelatentdebrisquantity Nodifference Latentdebrisconsistsof85%
dirt/dustand15%fiber Latentdebrisconsistsof85%
dirt/dustand15%fiber Nodifference
PublicMeetingMay23,2013 22 The following discussion of unqualified coatings debris generation (Item 5.a.1) is intended to provide an indication of the level of detail planned for the responses.
PublicMeetingMay23,2013 23 5.a.1) Failure timing, failure amounts, and debris characteristics of unqualified coatings.
Topical Area: Debris Generation STP Response:
Input parameters used for failure timing, failure amounts, and characteristics of unqualified coatings are provided in Volume 3.
Description of the method, basis, and assumptions used to develop the unqualified coatings input parameters is provided in a plant-specific unqualified coatings calculation.
As an example of the detailed information that will be provided in the revised submittal:
PublicMeetingMay23,2013 24 Example Response Unqualified Coatings Type Upper Containment Quantity (lbm)
Lower Containment Quantity (lbm)
Reactor Cavity Quantity (lbm)
Total Quantity (lbm)
Epoxy 295 (15%)
36 (2%)
1,574 (83%)
1,905 IOZ 305 (83%)
64 (17%)
0 (0%)
369 Alkyd 146 (54%)
125 (46%)
0 (0%)
271 Baked Enamel 0 (0%)
267 (100%)
0 (0%)
267 Intumescent 0 (0%)
2 (100%)
0 (0%)
2
PublicMeetingMay23,2013 25 Example Response
PublicMeetingMay23,2013 26 Time (Hours)
Time Dependent Failure 0 - 24 0.060
- Ffail 24 - 48 0.067
- Ffail 48 - 72 0.054
- Ffail 72 - 96 0.054
- Ffail 96 - 124 0.107
- Ffail 124 - 148 0.040
- Ffail 148 - 172 0.047
- Ffail 172 - 192 0.040
- Ffail 192 - 216 0.040
- Ffail 216 - 240 0.040
- Ffail Example Response
PublicMeetingMay23,2013 27 244lbm/ft3 Fines:4 20m particles UnqualifiedIOZ DebrisType DebrisSize Microscopic Density UnqualifiedEpoxy Fines:6milparticles 124lbm/ft3 FineChips:0.0156x15mil SmallChips:0.1250.5x15mil LargeChips:0.52.0x15mil CurledChips:0.52.0x15mil UnqualifiedAlkyd Fines:4 20m particles 207lbm/ft3 UnqualifiedBakedEnamel Fines:4 20m particles 93lbm/ft3 Example Response
PublicMeetingMay23,2013 28 Chemical Effects
PublicMeetingMay23,2013 29 Chemical Effects in STP Submittal - Overview In-vessel
WCAP-16793 (cold leg breaks)
Adequate flow through alternate path for all hot leg breaks and for small cold leg breaks.
Strainer head loss
STP-specific testing helped to confirm that chemical products do not form or form in small enough quantities that they are not deleterious for prototypical conditions.
Conservatively applied multipliers on strainer head loss:
5 times multiplier on conventional head loss calculation
Multiplier distributions for chemical head loss based on break size.
SBLOCA 2.3 mean (15.4 maximum)
MBLOCA 2.5 mean (18.2 maximum)
LBLOCA 3.0 mean (24.0 maximum)
PublicMeetingMay23,2013 30 Topical Area: Chemical Effects NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Corrosionanddissolutionof metalsandinsulationin containmentisafunctionof temperature,pH,andwater volume.Acceptedmodelis WCAP16530NP.
WCAP16530NPmodelusedto calculatecorrosionforwiderangeof scenarios,andinformengineering judgmentforchemicaleffectsbump upfactors.
Overallchemicaleffects evaluationisanewapproachas documentedinVolume3CASA GrandeAnalysis.
100%ofmaterialinsolutionwill precipitate.
Somematerialinsolutionmaynot precipitatedependingonthe temperaturedependentsolubility limitoftheprecipitate.
Overallchemicaleffects evaluationisanewapproachas inVolume3CASAGrande Analysis.
Precipitatescanbesimulated usingthesurrogaterecipe providedinWCAP16530NP.
Chemicalproductsgenerallyappear tobemorebenignthanWCAP surrogate.
Overallchemicaleffects evaluationisanewapproachas documentedinVolume3CASA GrandeAnalysis.
PublicMeetingMay23,2013 31 5.a.6) Chemical effects corrosion and dissolution models.
Topical Area: Chemical Effects STP Response:
Corrosion and dissolution models are part of the overall chemical effects analysis; the approach used to account for chemical effects head loss is documented in Volume 3 CASA Grande Analysis.
New models were not developed for corrosion and dissolution, but the WCAP-16530-NP methodology was used to determine the range of potential chemical product quantities for various break scenarios as documented in a plant-specific calculation.
PublicMeetingMay23,2013 32 5.a.7) Basis for excluding any plant materials from chemical testing.
Topical Area: Chemical Effects STP Response:
Copper, lead, carbon steel, Microtherm, alkyd coatings, and epoxy coatings were not included in the integrated tests based either on minimal exposure in the STP containment or previous testing that indicated negligible effects.
PublicMeetingMay23,2013 33 5.a.8) Chemical precipitation models - amount, type, head loss effect.
Topical Area: Chemical Effects STP Response:
Chemical precipitation inputs are addressed in the 5.a.6 response.
Head loss effects addressed as part of the 5.a.11 response.
PublicMeetingMay23,2013 34 5.a.9) Disposition of chemical effects Phenomena Identification and Ranking Table open items.
Topical Area: Chemical Effects STP Response:
Methods used to address PIRT issues will be documented with the revised submittal.
PublicMeetingMay23,2013 35 Topical Area: Strainer Head Loss NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Performplantspecificheadloss testingofthebounding scenario(s)withaprototype strainermodule.
UsetheNUREG/CR6224correlationso thatheadlosscanbeevaluatedatthe fullrangeofscenarios.
Approachdocumentedin Volume3CASAGrande Analysis.
Addresschemicaleffectshead lossusingWCAP16530NP surrogatesinprototypestrainer testing.
Addresschemicaleffectsheadloss withbumpupfactorconditional probabilitydistributions.
Overallchemicaleffects evaluationisanewapproach asdocumentedinVolume3 CASAGrandeAnalysis.
Minimumfiberquantity equivalentto1/16inchdebris bedonthestrainersisrequiredto formathinbed.
Minimumfiberquantityequivalentto 1/16inchdebrisbedonthestrainersis requiredtoformathinbed.
Nodifference Boundingstrainerheadloss comparedtoboundingNPSH marginandboundingstructural margintodeterminewhetherthe pumpsorstrainerwouldfail.
Timedependentstrainerheadloss comparedtotimedependentNPSH marginandboundingstructuralmargin todeterminewhetherthepumpsor strainerwouldfail.
Similarengineeringmodelas documentedinVolume3CASA GrandeAnalysis.
PublicMeetingMay23,2013 36 5.a.10) Head loss model.
Topical Area: Strainer Head Loss STP Response:
Basic head loss model is consistent with the NUREG/CR-6224 correlation as documented in Volume 3 CASA Grande Analysis.
Limited head loss testing used to help confirm that the NUREG/CR-6224 model provided reasonable predictions for STP conditions is documented in a head loss test report.
PublicMeetingMay23,2013 37 5.a.11) Chemical effects on head loss (bump-up factor) model.
Topical Area: Strainer Head Loss STP Response:
Multiplier factor probability distributions that are dependent on break size were used to account for chemical effects head loss; the basis for the probability distributions is documented in Volume 3 CASA Grande Analysis.
Based on engineering judgment multipliers were applied to the NUREG/CR-6224 correlation to account for uncertainties in chemical effects head loss.
PublicMeetingMay23,2013 38 Questions and Comments
PublicMeetingMay23,2013 39 NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Logictreeapproachtoanalyzing transportphases:blowdown, washdown,poolfill, recirculation,anderosion Logictreeapproachtoanalyzing transportphases:blowdown, washdown,poolfill,recirculation, anderosion Nodifference Alllargepiecesandaportionof smallpiecesarecapturedwhen blowdown flowpassesthrough grating.
Finestransportproportionalto containmentflow,gratingand miscellaneousobstructionscapture somesmallandlargepieces.
Similarmethodspreviously acceptedbyNRCfor deterministicevaluations 100%washdown offines,limited creditforholdupofsmall pieces,and0%washdown of largepiecesthroughgrating 100%washdown offines.Creditfor holdupofsomesmallpiecedebris ongrating.0%washdown oflarge piecesthroughgrating.
Includessomenew methodologyas documentedinVolume3 CASAGrandeAnalysis.
Poolfilltransporttoinactive cavitiesmustbelimitedto15%
unlesssufficientjustificationcan bemade Poolfilltransporttoinactive cavitiesislessthan15%.
Methodologyisbasedon exponentialequationwithuniform mixingoffines.
Similarmethodspreviously acceptedbyNRCfor deterministicevaluations Topical Area: Debris Transport
PublicMeetingMay23,2013 40 NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison CFDrefinementsareappropriate forrecirculationtransport,buta blanketassumptionthatall debrisisuniformlydistributedis notappropriate.
Recirculationtransportbasedon conservativeCFDsimulations developedforthedeterministic STPdebristransportcalculation.
Alldebriswasnotassumedtobe uniformlydistributed.
MethodologyforCFD modelingandrecirculation transportanalysis previouslyacceptedbyNRC fordeterministic evaluations.
90%erosionshouldbeusedfor nontransportingpiecesof unjacketedfiberglassinthe recirculationpoolunless additionaltestingisperformed tojustifyalowerfraction.
Probabilitydistributionwitha rangeoflessthan10%erosion basedonAlion testing.
Valuesarerelativelyclose totheexperimentally determined10%erosion valuepreviouslyaccepted bytheNRCfor deterministicevaluations.
1%erosionofsmallorlarge piecesoffiberglassheldupin uppercontainment.
1%erosionofsmallorlarge piecesoffiberglassheldupin uppercontainment.
Nodifference.
Minimalpreviousanalysison timedependenttransport.
Timedependenttransport evaluatedforpoolfill,washdown, recirculation,anderosion.
Severalaspectsofthetime dependenttransportare newengineeringmodelsas documentedinVolume3 CASAGrandeAnalysis.
Topical Area: Debris Transport
PublicMeetingMay23,2013 41 5.a.2) Capture of small and large pieces of debris on gratings and obstructions.
Topical Area: Debris Transport STP Response:
Methodology for debris capture on gratings and obstructions during the blowdown phase is documented in an engineering calculation based on plant-specific features (locations of grating, etc.) and applicable test data.
Debris capture on grating and obstructions is related to the blowdown transport. Transport fractions that were used are documented in Volume 3 CASA Grande Analysis.
PublicMeetingMay23,2013 42 5.a.3) Washdown transport holdups.
Topical Area: Debris Transport STP Response:
Description of the method, basis, and assumptions used to develop the washdown transport fractions is provided in a plant-specific debris transport calculation.
Washdown transport holdups are related to the overall washdown transport; the transport fractions that were used are documented in Volume 3 CASA Grande Analysis.
PublicMeetingMay23,2013 43 5.a.4) Non-uniform debris distribution at the onset of recirculation.
Topical Area: Debris Transport STP Response:
The debris distribution at the start of recirculation is related to the recirculation transport; the transport fractions that were used are documented in Volume 3 CASA Grande Analysis.
Description of the method, basis, and assumptions used to develop the recirculation transport fractions is provided in a plant-specific debris transport calculation.
PublicMeetingMay23,2013 44 5.a.5) Time dependent transport.
Topical Area: Debris Transport STP Response:
Time-dependent arrival of debris on the strainer is documented in Volume 3 CASA Grande Analysis.
Description of the method, basis, and assumptions used to determine the time-dependent transport is provided in a plant-specific debris transport calculation.
PublicMeetingMay23,2013 45 Topical Area: Air Intrusion NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Releaseofairbubblesatthe strainercalculatedbasedonthe watertemperature, submergence,strainerheadloss, andflowrate.
Releaseofairbubblesatthestrainer calculatedbasedonthewater temperature,submergence,strainer headloss,andflowrate.
Nodifference NPSHmarginadjustedbasedon thevoidfractionatthepump inlet NPSHmarginadjustedbasedonthe voidfractionatthepumpinlet Nodifference Voidfractionatpumpscompared toasteadystatevoidfractionof 2%todeterminewhetherthe pumpswouldfail.
Voidfractionatpumpscomparedtoa steadystatevoidfractionof2%to determinewhetherthepumpswould fail.
Nodifference.
PublicMeetingMay23,2013 46 Topical Area: Debris Penetration NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Performplantspecificfiber penetrationtestingofthe boundingscenario(s)witha prototypestrainermodule.
Developafiberpenetrationcorrelation asafunctionofstrainerflowrateand fiberaccumulationbasedonaseriesof penetrationtests.
Newapproachdocumented inVolume3CASAGrande Analysis.
100%penetrationof transportableparticulateand chemicalprecipitates.
100%penetrationoftransportable particulateandchemicalprecipitates.
Nodifference.
PublicMeetingMay23,2013 47 5.a.12) Fiber bypass amounts and amounts reaching the core for various scenarios.
Topical Area: Debris Penetration STP Response:
The methodology and model for determining time-dependent penetration and accumulation on the core is documented in Volume 3 CASA Grande Analysis.
Testing used to develop the penetration correlation is documented in a penetration test report, and the correlation parameters are documented in a plant-specific data analysis report.
PublicMeetingMay23,2013 48 Topical Area: Ex-Vessel Downstream Effects NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Evaluateexvesselwearand cloggingbasedonthe methodologyinWCAP16406P Evaluateexvesselwearandclogging basedonthemethodologyinWCAP 16406P Nodifference.
PublicMeetingMay23,2013 49 Topical Area: In-Vessel Downstream Effects NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Comparefiberquantityoncoreto bounding15g/FAlimitbasedon WCAP16793NP.
UseRELAP5simulationstoshowthat coldlegsmallbreakLOCAs andallhot legLOCAs wouldnotgotocore damagewithfullblockageatthebase ofthecore.Formediumandlargecold legbreaks,useWCAP16793Pforfiber limitonthecore.
Newapproachdocumented inVolume3CASAGrande Analysis.
Evaluatereducedheattransfer duetodepositiononfuelrods usingLOCADMsoftware.
Evaluatereducedheattransferdueto depositiononfuelrodsusingLOCADM software.
Nodifference.
PublicMeetingMay23,2013 50 5.a.13) Fiber limits for in-vessel evaluations.
Topical Area: In-Vessel Downstream Effects STP Response:
Fiber limits for core blockage and boron precipitation are described in Volume 3 CASA Grande Analysis.
Limits are based in part on thermal-hydraulic modeling documented in a plant specific report, as well as fuel head loss test results documented in WCAP-16793-NP.
PublicMeetingMay23,2013 51 5.a.14) Thermal-hydraulic analysis for in-vessel evaluations.
Topical Area: In-Vessel Downstream Effects STP Response:
Thermal-hydraulic results are described at a high level in Volume 3 CASA Grande Analysis, and a detailed description of the analysis is described in plant-specific reports.
PublicMeetingMay23,2013 52 Topical Area: Boron Precipitation NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Nocurrentlyaccepted methodology.
Evaluatefiberaccumulationonthe coreforcoldlegbreaksduringcoldleg injection.Assumethat7.5g/FAof fiberissufficienttoformadebrisbed thatwouldpreventnaturalmixing betweenthecoreandlowerplenum.
Assumefailureduetoboron precipitationifthisquantityarrives priortohotlegswitchover.
Newapproach documented inVolume3CASAGrande Analysis.
PublicMeetingMay23,2013 53 5.a.15) Boric acid precipitation evaluations.
Topical Area: Boron Precipitation STP Response:
Methodology for addressing boric acid precipitation is described in Volume 3 CASA Grande Analysis.
PublicMeetingMay23,2013 54 Questions and Comments
PublicMeetingMay23,2013 55 5.a.16) Methodology for determination and implementation of physical effects probability distributions.
Probability Distributions STP Response:
Probability distributions for each input parameter are described in Volume 3 CASA Grande Analysis.
Descriptions of the method, basis, and assumptions used to develop the probability distributions are provided in several different plant-specific calculations and reports.
PublicMeetingMay23,2013 56 5.d.
Please provide sufficient detail necessary to assess the treatment of uncertainty. While several known categories of uncertainty are identified (zone of influence, chemical effects, debris transport, etc.), the mechanistic models and associated parametric factors used in the analysis are not identified, nor are probability density functions for the parameters provided (Enclosure 4, Section 2.5). Please provide this information.
Treatment of Uncertainty STP Response:
Uncertainty associated with the various CASA Grande input parameters is quantified using the probability distributions for the parameters.
Different approaches are used to develop the CASA Grande input parameters depending on the data that is available; these approaches are documented in several different plant-specific calculations and reports.
PublicMeetingMay23,2013 57 Questions and Comments
PublicMeetingMay23,2013 58 5.b.
Regarding DID, please address how DID is maintained to account for scenarios that are predicted to lead to failure.
One method of maintaining DID is to demonstrate that the operators can detect and mitigate inadequate flow through the recirculation strainer and inadequate core cooling. Please describe the supporting evaluations that demonstrate DID actions will be effective.
Defense-in-Depth STP Response:
The proposed change to the UFSAR does not involve a physical change to the plant or changes to the operation of the plant.
STP DID approach incorporates plant modifications previously implemented to address GSI-191 concerns. These modifications are included in the site-specific PRA model for evaluation of the as-built and as-operated plant.
PublicMeetingMay23,2013 59 Previous modifications implemented to address GSI-191 are not part of the application, but are included in the site-specific model:
Defense-in-Depth (DID)
Original sump screens were replaced with new advanced design, passive sump strainers.
New strainers satisfy the current licensing basis requirements for debris loading.
Maintain independence and redundancy of the ECCS and CSS sump configurations, with each train pipe inlet provided from its own sump and strainer, and no shared components between trains.
Surface area of each strainer increased from ~150 ft2 to ~1800 ft2.
Strainer perforations reduced from 0.25 inches to 0.095 inches in diameter.
Calcium silicate insulation (Marinite) around reactor vessel nozzles has been replaced with removable NUKON fiberglass insulation.
PublicMeetingMay23,2013 60 Defense-in-Depth (DID)
Operator Actions for DID:
Describes Operator actions for maintaining DID Actions and plant design features for preventing, detecting, and mitigating inadequate recirculation strainer flow and inadequate core cooling Followed guidance in NEI letter on DID strategies (March 5, 2012)
Actions that were described in the STP responses to Bulletin 2003-01 and Generic Letter 2004-02 remain in effect.
Operators will inform the Technical Support Center (TSC) of the condition, and the TSC will evaluate and recommend actions as necessary
PublicMeetingMay23,2013 61 Defense-in-Depth (DID)
Supporting Evaluations
Training - the capabilities of the operators are evaluated through initial and continuing operator training, and the use of simulator exercises.
Procedure implementation - STP EOPs are evaluated during the procedure development, validation, and approval. Procedures are supported by site-specific analyses, as required.
Industry guidance - STP EOP directions are based on generic guidance provided by the Westinghouse Owners Group (WOG)
Emergency Response Guidelines (ERGs), as supported by vendor analyses.
PublicMeetingMay23,2013 62 5.c.
Please provide supporting evaluations that demonstrate that the barriers for the release of radioactivity will be maintained with sufficient safety margin.
Barriers for Release of Radioactivity STP Response:
The physical barriers discussed in Volume 1 Project Summary as part of the RG 1.174 application are:
The containment The reactor coolant pressure boundary The fuel cladding In addition, evaluation of emergency plan actions are discussed.
PublicMeetingMay23,2013 63 Questions and Comments
PublicMeetingMay23,2013 64 At the beginning of the meeting, the stated desired outcomes were to gain a clear understanding of:
The structure of the submittal The submittal will address the completeness concern of the staff The level of detail that will be provided in the submittal What will be in the submittal and what will be provided to the staff for audit Desired Outcomes - Recap