ML13140A256
| ML13140A256 | |
| Person / Time | |
|---|---|
| Site: | South Texas  (NPF-076, NPF-080) |
| Issue date: | 05/20/2013 |
| From: | South Texas |
| To: | Plant Licensing Branch IV |
| Singal B | |
| Shared Package | |
| ML13140A284 | List: |
| References | |
| GSI-191, TAC MF0613, TAC MF0614 | |
| Download: ML13140A256 (66) | |
Text
PublicMeetingMay23,2013 1
South Texas Project Units 1 & 2 STP Pilot Submittal for Risk-Informed Approach to Resolving GSI-191 DRAFT DRAFT
PublicMeetingMay23,2013 2
Introduction
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
Questions and comments Agenda DRAFT DRAFT
PublicMeetingMay23,2013 3
Attendees 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 Tim Sande Enercon Bruce Letellier Alion Jeremy Tejada University of Texas at Austin Rodolfo Vaghetto Texas A&M University Kerry Howe University of New Mexico Don Wakefield ABS Consulting Steven Frantz Morgan Lewis Zahra Mohaghegh University of Illinois at Champaign-Urbana DRAFT DRAFT
PublicMeetingMay23,2013 4
NRC has accepted the proposal to submit a revised STP pilot application for a risk-informed approach to resolving GSI-191 by June 20, 2013.
The revised submittal will include four exemption requests pursuant to 10 CFR 50.12 to support the proposed change to the licensing basis:
50.46(b)(5), and GDC-35, GDC-38 and GDC-41, each provided by separate enclosure.
Impacts on other regulatory requirements addressed in the evaluations.
Additional information to be included is discussed later in the presentation.
The revised submittal will include a license amendment request (LAR) pursuant to 10 CFR 50.90 for NRC approval of the proposed change to the STP Units 1 & 2 Updated Final Safety Analysis Report (UFSAR).
LAR regulatory evaluation ties to exemption requests.
Content follows guidance of NEI 06-02.
No significant hazards consideration 10 CFR 50.92, and categorical exclusion evaluation for 10 CFR 51.22(c)(9).
Markup of the change to the UFSAR submitted for NRC approval.
Overview of Planned Revised Submittal DRAFT DRAFT
PublicMeetingMay23,2013 5
An attachment will be included that addresses the information requirements identified in the NRC acceptance review letter.
Describes the additional information included in the revised submittal that is responsive to each item.
References to information included to facilitate the staffs completion of its acceptance review.
Additional supporting information previously referenced in the Project Summary (Volume 1) will be included as enclosures:
Volume 2 Probabilistic Risk Assessment (PRA)
Volume 3 Engineering (CASA Grande) Analysis Overview of Planned Revised Submittal DRAFT DRAFT
PublicMeetingMay23,2013 6
Attachment to the Cover Letter
Responses to NRC items needed for acceptance review with references to additional information included in the revised submittal, and a summary of changes from the 1/31/2013 submittal.
Generic risk-informed methodology for resolving GSI-191.
Enclosures 2-1 through 2-4
STP-specific 10 CFR 50.12 exemption requests for ECCS acceptance criterion 10 CFR 50.46(b)(5), GDC-35, GDC-38, and GDC-41.
10 CFR 50.90 LAR with changes to the STP UFSAR for NRC approval.
Enclosures 4-1 through 4-3
Volume 1 Project Summary, Volume 2 PRA, and Volume 3 Engineering (CASA Grande) Analysis Revised Submittal - Outline DRAFT DRAFT
PublicMeetingMay23,2013 7
Addresses the required content of a RG 1.174 application using the same section numbering scheme as in RG 1.174.
Summarizes the generic methodology and how the risk metrics associated with the residual risk of GSI-191 are determined:
The overall analysis approach describing how engineering analyses are used in a risk-informed framework to support the PRA.
Identifies where the methods adopted for the STP approach involve deviations from those previously approved for deterministic (Option 1) resolution of GSI-191, primarily NEI 04-07.
Quantifies the change in risk associated with the concerns raised in GSI-191 in the as-built, as-operated plant (such as fibrous debris beds, chemical effects, in-vessel fiber loads, etc.).
Summarizes the plant-specific implementation of the methodology.
Volume 1 Project Summary DRAFT DRAFT
PublicMeetingMay23,2013 8
Describes the Probabilistic Risk Assessment (PRA) treatment of GSI-191 safety issues and interface with deterministic analyses
Provides quantification of CDF and LERF risk metrics for comparison to RG 1.174 acceptance guidelines.
For STP Units 1 & 2, the change in risk associated with GSI-191 is:
~ 1.1E-8/yr (delta CDF) and ~ 8.6E-12/yr (delta LERF)
Far less than the threshold for Region III Very Small Changes
Provides PRA uncertainty quantification.
Volume 2 PRA - Summary DRAFT DRAFT
PublicMeetingMay23,2013 9
Volume 3 is a technical evaluation that provides a high-level description of the phenomenological portion of the overall risk-informed GSI-191 evaluation.
Provides a detailed summary of supporting engineering analyses (CASA Grande evaluation) including:
Input parameters
Assumptions
Methodology
Analysis
Results
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.
Volume 3 - Summary DRAFT DRAFT
PublicMeetingMay23,2013 10 Volume 3 provides summary descriptions of the STP approach:
Based on applying the NRC approved deterministic methods from NEI 04-07 and other NRC-approved guidance to model the inputs to the PRA.
Differences are identified and discussed to provide a basis for starting the NRC review of the STP pilot.
Sufficient detail is provided to identify STP-specific information so that licensees following the approach can identify plant-specific differences and deviations from STP, as the starting point for these subsequent reviews.
Volume 3 - Summary DRAFT DRAFT
PublicMeetingMay23,2013 11
A wide variety of input parameters are required for a GSI-191 evaluation. Volume 3 does not provide details for how these inputs were determined, but lists the input values with references to source calculations.
Assumptions that were used in the CASA Grande evaluation are listed and justification is provided. Assumptions that were used to develop specific input parameters are documented in the source calculations.
The methods used for the CASA Grande evaluation are described at a high level up front, and in more detail in the analysis section for each topical area.
Volume 3 - Summary DRAFT DRAFT
PublicMeetingMay23,2013 12
The analysis sections include discussion and illustrations of the physical models for each topical area, along with the equations that are solved in CASA Grande. A description of how each physical model is linked together is also provided.
The results of the CASA Grande evaluation are presented in the form of conditional probabilities of sump failure, core blockage, and boron precipitation for small, medium, and large breaks. These conditional failure probabilities are a direct input for the PRA evaluation (Volume 2) to determine CDF and LERF.
Volume 3 - Summary DRAFT DRAFT
PublicMeetingMay23,2013 13 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 DRAFT DRAFT
PublicMeetingMay23,2013 14
- 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.
DRAFT DRAFT
PublicMeetingMay23,2013 15
No exceptions from the explicit acceptance criteria or design criteria provided in the regulatory requirements.
The exemption requests are from the implicit requirements to use a deterministic method to demonstrate acceptable design and performance.
The current licensing basis deterministic method of evaluating sump performance meets the regulatory requirements, but has not been demonstrated to fully resolve GSI-191.
Exemption requests support the LAR-proposed change to the UFSAR that reconstitutes the licensing basis using a risk-informed method that meets the key principles of RG 1.174 and demonstrates the risk associated with GSI-191 concerns is Very Small (Region III in RG 1.174).
Acceptable design basis of the ECCS containment emergency sumps and suction strainers supports the long-term cooling licensing basis for ECCS acceptance criterion 10 CFR 50.46(b)(5) and the licensing basis for ECCS and CSS design requirements specified in GDC-35, GDC-38 and GDC-41.
The current licensing basis for ECCS and CSS compliance with 10 CFR 50.46, including the accident analyses provided in UFSAR Chapter 15, and the GDC remain unchanged.
Exemption Requests - Summary DRAFT DRAFT
PublicMeetingMay23,2013 16
- 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 an LAR pursuant to 10 CFR 50.90 with the proposed changes to the UFSAR for NRC approval, and a no significant hazards consideration.
DRAFT DRAFT
PublicMeetingMay23,2013 17 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.
DRAFT DRAFT
PublicMeetingMay23,2013 18
- 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.
DRAFT DRAFT
PublicMeetingMay23,2013 19
- 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, to include:
Consideration of the categories specified in 10 CFR 50.36(c).
Surveillance Requirements in effect that support the proposed change.
TS definition of Operable/Operability adequately addressing the proposed change as related to the required support function provided by the containment sumps and strainers for ECCS and CSS, and no changes are needed to operability requirements or existing TS Action Statements.
Conforming changes to the TS Bases (for information only) will be included in the markups submitted with the LAR.
DRAFT DRAFT
PublicMeetingMay23,2013 20
- 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 DRAFT DRAFT
PublicMeetingMay23,2013 21 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 DRAFT DRAFT
PublicMeetingMay23,2013 22 NRC Approved GSI-191 Methods Methodology for GSI-191 evaluation has evolved, and NRC accepted methods are documented in various sources:
NEI 04-07 Volumes 1 and 2 (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).
Revised submittal will describe the methods, bases, assumptions, acceptance criteria, and results for each of these areas.
DRAFT DRAFT
PublicMeetingMay23,2013 23 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 DRAFT DRAFT
PublicMeetingMay23,2013 24 Topical Area: Debris Generation NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison 100%failureforallunqualified coatingsdebris Timedependentandpartial failureofunqualifiedcoatings basedonavailabledata.
Newengineeringmodel documentedinVolume3.
Unqualifiedcoatingsfailas10m particlesifthestrainerisfully coveredoraschipsifafiberbed wouldnotbeformed.
Unqualifiedcoatingsfailinasize distributionbasedoncoating typeandavailabledata.
Similarmethodspreviously acceptedbyNRCfor deterministicevaluations Plantspecificwalkdownsrequiredto determinelatentdebrisquantity STPspecificwalkdownusedto determinelatentdebrisquantity Nodifference Latentdebrisconsistsof85%
dirt/dustand15%fiber Latentdebrisconsistsof85%
dirt/dustand15%fiber Nodifference DRAFT DRAFT
PublicMeetingMay23,2013 25 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:
DRAFT DRAFT
PublicMeetingMay23,2013 26 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 DRAFT DRAFT
PublicMeetingMay23,2013 27 Example Response DRAFT DRAFT
PublicMeetingMay23,2013 28 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 DRAFT DRAFT
PublicMeetingMay23,2013 29 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 DRAFT DRAFT
PublicMeetingMay23,2013 30 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 onconcretefloorsandgrating.0%
washdown oflargepiecesthrough grating.
Includessomenew methodologyas documentedinVolume3.
Poolfilltransporttoinactive cavitiesmustbelimitedto15%
unlesssufficientjustificationcan bemade Poolfilltransporttoinactive cavitiesislessthan15%.
Methodologyisbasedon exponentialequationwithuniform mixingoffines.
Similarmethodspreviously acceptedbyNRCfor deterministicevaluations Topical Area: Debris Transport DRAFT DRAFT
PublicMeetingMay23,2013 31 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.
Topical Area: Debris Transport DRAFT DRAFT
PublicMeetingMay23,2013 32 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.
Description of the method, basis, and assumptions used to develop the blowdown transport fractions is provided in a plant-specific debris transport calculation.
The debris capture methods have been previously accepted by the NRC, but the retention fractions on gratings and other structures are based on the drywell debris transport study (DDTS), and multiple break locations are considered.
Fines are transported easily and distributed according to the volume fraction of the upper containment.
Some of the small debris is also transported to upper containment in proportion to the volume of the compartment in which it is generated.
DRAFT DRAFT
PublicMeetingMay23,2013 33 5.a.3) Washdown transport holdups.
Topical Area: Debris Transport STP Response:
Washdown transport holdups are related to the overall washdown transport; the transport fractions that were used are documented in Volume 3
Description of the method, basis, and assumptions used to develop the washdown transport fractions is provided in a plant-specific debris transport calculation.
DRAFT DRAFT
PublicMeetingMay23,2013 34 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
Description of the method, basis, and assumptions used to develop the recirculation transport fractions is provided in a plant-specific debris transport calculation.
DRAFT DRAFT
PublicMeetingMay23,2013 35 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.
Description of the method, basis, and assumptions used to determine the time-dependent transport is provided in a plant-specific debris transport calculation DRAFT DRAFT
PublicMeetingMay23,2013 36 Topical Area: Chemical Effects NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Corrosionanddissolutionof metalsandinsulationin containmentisafunctionof temperature,pH,andwater volume.Acceptedmodelis WCAP16530NP.
Corrosionanddissolutionofmetals andinsulationincontainmentisa functionoftemperature,pH,water volume,andpoolchemistry.New modelbeingdevelopedforSTP conditions.
Severalaspectsofthecorrosion anddissolutionmodelsarenew engineeringmodelsas documentedinVolume3.
100%ofmaterialinsolutionwill precipitate.
Somematerialinsolutionmaynot precipitatedependingonthe solubilitylimitoftheprecipitate.
Newengineeringmodel documentedinVolume3.
Precipitatescanbesimulated usingthesurrogaterecipe providedinWCAP16530NP.
Precipitatesaremuchsmallerand morebenignthanWCAPsurrogate.
Newengineeringmodel documentedinVolume3.
DRAFT DRAFT
PublicMeetingMay23,2013 37 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
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 DRAFT DRAFT
PublicMeetingMay23,2013 38 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.
DRAFT DRAFT
PublicMeetingMay23,2013 39 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.
DRAFT DRAFT
PublicMeetingMay23,2013 40 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.
DRAFT DRAFT
PublicMeetingMay23,2013 41 Topical Area: Strainer Head Loss NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Performplantspecificheadloss testingofthebounding scenario(s)withaprototype strainermodule.
ModifytheNUREG/CR6224 correlationtoaddressoldACRS commentsandSTPspecificconditions sothatheadlosscanbeevaluatedat thefullrangeofscenarios.
Severalaspectsofthe engineeringmodelsarenewas documentedinVolume3.
Addresschemicaleffectshead lossusingWCAP16530NP surrogatesinprototypestrainer testing.
Addresschemicaleffectsheadloss withasimplebumpupfactorsimilarto the2011quantificationusingtheCHLE testingthathasbeenperformedsofar tojustifytheconservatism.
Newengineeringmodel documentedinVolume3.
Minimumfiberquantity equivalentto1/16inchdebris bedonthestrainersisrequiredto formathinbed.
Minimumfiberquantityequivalentto 1/16inchdebrisbedonthestrainersis requiredtoformathinbed.
Nodifference Boundingstrainerheadloss comparedtoboundingNPSH marginandboundingstructural margintodeterminewhetherthe pumpsorstrainerwouldfail.
Timedependentstrainerheadloss comparedtotimedependentNPSH marginandboundingstructuralmargin todeterminewhetherthepumpsor strainerwouldfail.
Similarengineeringmodelas documentedinVolume3.
DRAFT DRAFT
PublicMeetingMay23,2013 42 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.
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.
DRAFT DRAFT
PublicMeetingMay23,2013 43 5.a.11) Chemical effects on head loss (bump-up factor) model.
Topical Area: Strainer Head Loss STP Response:
Bump-up 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.
DRAFT DRAFT
PublicMeetingMay23,2013 44 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 confirmed chemical products do not form or form in small enough quantities that they are not deleterious.
Conservatively applied multipliers on strainer head loss:
5X multiplier on conventional head loss calculation; and 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)
DRAFT DRAFT
PublicMeetingMay23,2013 45 Chemical Effects in STP Submittal - Overview
Other testing helps support small chemical effects on strainer head loss for STP:
STP-specific deterministic test at Alden (2008) showed approximately 2X increase in head loss using conservative WCAP precipitates.
Integrated Chemical Effects Test (ICET) program Test #2, representative of the STP post accident chemistry, indicated relatively insignificant chemical effects with much large debris quantities than STP.
Vogtle integrated testing (VUEZ) with similar conditions to STP showed relatively insignificant chemical effects.
DRAFT DRAFT
PublicMeetingMay23,2013 46 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.
DRAFT DRAFT
PublicMeetingMay23,2013 47 Topical Area: Debris Penetration NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Performplantspecificfiber penetrationtestingofthe boundingscenario(s)witha prototypestrainermodule.
Developafiberpenetrationcorrelation asafunctionofstrainerflowrateand fiberaccumulationbasedonaseriesof penetrationtests.
Newengineeringmodel documentedinVolume3.
100%penetrationof transportableparticulateand chemicalprecipitates.
100%penetrationoftransportable particulateandchemicalprecipitates.
Nodifference.
DRAFT DRAFT
PublicMeetingMay23,2013 48 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
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 DRAFT DRAFT
PublicMeetingMay23,2013 49 Topical Area: Ex-Vessel Downstream Effects NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Evaluateexvesselwearand cloggingbasedonthe methodologyinWCAP16406P Evaluateexvesselwearandclogging basedonthemethodologyinWCAP 16406P Nodifference.
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PublicMeetingMay23,2013 50 Topical Area: In-Vessel Downstream Effects NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Comparefiberquantityoncoreto bounding15g/FAlimitbasedon WCAP16793NP.
UseRELAP5simulationstoshowthat coldlegSBLOCAs andallhotlegLOCAs wouldnotgotocoredamagewithfull blockageatthebaseofthecore.Use WCAP17057Ptestswithconditions closertotheSTPtojustifyan appropriatefiberlimitonthecore.
Newengineeringmodel documentedinVolume3.
Evaluatereducedheattransfer duetodepositiononfuelrods usingLOCADMsoftware.
Evaluatereducedheattransferdueto depositiononfuelrodsusingLOCADM software.
Nodifference.
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PublicMeetingMay23,2013 51 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
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 DRAFT DRAFT
PublicMeetingMay23,2013 52 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, and a detailed description of the analysis is described in plant-specific reports.
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PublicMeetingMay23,2013 53 Topical Area: Boron Precipitation NRCApprovedDeterministic Methods-NEI0407SER STPRiskInformedMethods Comparison Nocurrentlyaccepted methodology.
Evaluatefiberaccumulationonthe coreforcoldlegbreaksduringcoldleg injection.Assumethat7.5g/FAof fiberissufficienttoformadebrisbed thatwouldpreventnaturalmixing betweenthecoreandlowerplenum.
Assumefailureduetoboron precipitationifthisquantityarrives priortohotlegswitchover.
Newengineeringmodel documentedinVolume3.
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PublicMeetingMay23,2013 54 5.a.15) Boric acid precipitation evaluations.
Topical Area: Boron Precipitation STP Response:
Methodology for addressing boric acid precipitation is described in Volume 3.
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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
Description of the method, basis, and assumptions used to develop the probability distributions are provided in several different plant-specific calculations and reports.
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PublicMeetingMay23,2013 56 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 STP Units 1 & 2 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.
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PublicMeetingMay23,2013 57
Original sump screens were replaced with new advanced sump strainers designed by Performance Contracting Inc. (PCI)
New strainers satisfy the current licensing basis and are passive in design.
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 train increased from ~150 sq ft to ~1800 sq ft, providing increased assurance that sump flow will not be blocked by debris and NPSH available for ECCS and CSS pumps will be maintained.
Diameter of screen perforations reduced from 0.25 inches to 0.095 inches (perforated plate) and complex geometry of strainer design significantly reduced the potential for downstream debris effects.
Protective gratings for sump strainers were installed to preclude inadvertent damage to these component.
Defense-in-Depth (DID)
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PublicMeetingMay23,2013 58 Defense-in-Depth (DID)
Calcium silicate insulation (Marinite) around reactor vessel nozzles has been replaced with NUKON fiberglass insulation.
Significant contributor to the debris loading associated with one of the worst case LOCA scenarios for strainer head loss based on previous evaluations.
Concern that calcium silicate can combine with the tri-sodium phosphate (TSP) pH buffer during post-LOCA conditions to form calcium phosphate precipitates which could block strainers.
The previous STP debris generation analysis had accounted for this chemical debris and subsequent strainer testing had acceptable results, however to fully address the concern the insulation was replaced.
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PublicMeetingMay23,2013 59 Defense-in-Depth (DID)
Operator actions to detect and mitigate inadequate flow through the recirculation strainer and inadequate core cooling utilize STP procedures and design features to maintain DID.
Inadequate Recirculation Strainer Flow STP Emergency Operating Procedures (EOPs) provide specific steps for operators to prevent, detect, and mitigate recirculation strainer blockage:
Guidance for restoring recirculation or for alternate cooling methods if flow blockage occurs.
Refilling the refueling water storage tank (RWST) after verification of proper swap over to cold-leg recirculation.
Operator training on indications of and response to strainer clogging.
These actions are described in the STP responses to Bulletin 2003-01 and remain in effect.
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PublicMeetingMay23,2013 60 Defense-in-Depth (DID)
Inadequate Core Flow Methods for operators to prevent, detect, and mitigate a core flow blockage condition resulting from inadequate reactor coolant system (RCS) inventory or inadequate core heat removal are provided.
Primary detection methods include core exit thermocouples (CETs) and reactor vessel level monitoring.
Monitoring is initiated early in the EOPs through the Critical Safety Function Status Trees and performed continuously after completion of event diagnosis at appropriate frequency.
Additional detection of inadequate core cooling includes monitoring of containment pressure and containment sump level, RCS subcooling, containment radiation levels (indications and alarms).
Emergency Response Organization personnel in the Technical Support Center (TSC) or Emergency Operations Facility (EOF) will also provide oversight of plant status using these detection methods.
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PublicMeetingMay23,2013 61 Defense-in-Depth (DID)
To mitigate loss of core flow, EOP actions direct operators to restore cooling flow to the RCS:
Refilling the RWST.
Minimize break flow by cooling down and depressurizing the RCS, for example by steaming through the steam generators.
Aligning alternate injection paths
Operators will inform the TSC of the condition, and the TSC will evaluate and recommend actions as necessary to restore core cooling, including:
Reducing injection flow rate (securing ECCS pumps) to meet the minimal heat removal requirements
Use of hot leg injection flow path
Establish alternate injection paths from sources including the Volume Control Tank (VCT)
Refilling the RWST using normal makeup or fire protection system
Restarting Reactor Coolant Pumps
Flood containment DRAFT DRAFT
PublicMeetingMay23,2013 62 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.
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PublicMeetingMay23,2013 63 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:
STP Design for Containment Heat Removal:
Energy released to the containment atmosphere from the postulated accidents is removed by the Containment Spray System (CS) and Reactor Containment Fan Cooler System (RCFC).
Three groups of RCFCs, two fans per group (six fans total).
Following an accident, cooling water to RCFCs is supplied by the safety grade component cooling water (CCW) system.
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PublicMeetingMay23,2013 64 Barriers for Release of Radioactivity Response to 5.c. continued:
Containment integrity evaluations:
Based on study results, two trains of RCFCs are sufficient for containment heat removal if no containment spray pumps are operating.
Containment integrity is maintained if all the CS pumps are secured.
STP design as a PWR dry containment with safety-grade fan coolers is likely to survive a core melt situation, even with a loss of the containment emergency sump (NUREG-0869, Revision 1)
The proposed change does not impact any design or programmatic requirements for the reactor coolant pressure boundary, therefore does not affect the likelihood of a LOCA.
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PublicMeetingMay23,2013 65 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 input parameters is quantified using the probability distributions for the parameters.
Different approaches are used to develop the input parameters depending on the data that is available; these approaches are documented in several different plant-specific calculations and reports.
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PublicMeetingMay23,2013 66 Questions and Comments DRAFT DRAFT