ML13140A256
| ML13140A256 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| 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
DRAFT South Texas Project Units 1 & 2 STP Pilot Submittal for Risk-Informed Approach to Resolving GSI-191 Public Meeting May 23, 2013 1 DRAFT
DRAFT Agenda 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 Public Meeting May 23, 2013 2 DRAFT
DRAFT 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 Public Meeting May 23, 2013 3 DRAFT
DRAFT Overview of Planned Revised Submittal 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.
Public Meeting May 23, 2013 4 DRAFT
DRAFT Overview of Planned Revised Submittal 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 Public Meeting May 23, 2013 5 DRAFT
DRAFT Revised Submittal - Outline 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.
Enclosure 1 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.
Enclosure 3 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 Public Meeting May 23, 2013 6 DRAFT
DRAFT Volume 1 Project Summary 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.
Public Meeting May 23, 2013 7 DRAFT
DRAFT Volume 2 PRA - Summary 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.
Public Meeting May 23, 2013 8 DRAFT
DRAFT Volume 3 - Summary 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.
Public Meeting May 23, 2013 9 DRAFT
DRAFT Volume 3 - Summary 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.
Public Meeting May 23, 2013 10 DRAFT
DRAFT Volume 3 - Summary 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.
Public Meeting May 23, 2013 11 DRAFT
DRAFT Volume 3 - Summary 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.
Public Meeting May 23, 2013 12 DRAFT
DRAFT STP Responses to Acceptance Review Letter 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.
Public Meeting May 23, 2013 13 DRAFT
DRAFT Exemption Requests
- 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).
STP Response:
The revised exemption requests will correct the typographical error and address the required information.
Public Meeting May 23, 2013 14 DRAFT
DRAFT Exemption Requests - Summary 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.
Public Meeting May 23, 2013 15 DRAFT
DRAFT License Amendment Request
- 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.
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.
Public Meeting May 23, 2013 16 DRAFT
DRAFT 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.
Public Meeting May 23, 2013 17 DRAFT
DRAFT Environmental Review
- 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.
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.
Public Meeting May 23, 2013 18 DRAFT
DRAFT Technical Specifications
- 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.
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.
Public Meeting May 23, 2013 19 DRAFT
DRAFT Basis for the Proposed Change
- 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:
Public Meeting May 23, 2013 20 DRAFT
DRAFT Basis for the Proposed Change 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:
Public Meeting May 23, 2013 21 DRAFT
DRAFT 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.
Public Meeting May 23, 2013 22 DRAFT
DRAFT Topical Area: Debris Generation NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER Use spherical or hemispherical ZOI Use spherical or hemispherical No difference ZOI 17D ZOI for Nukon and Thermal 17D ZOI for Nukon and Thermal No difference Wrap Wrap 28.6D ZOI for Microtherm 28.6D ZOI for Microtherm No difference 4D ZOI for qualified coatings 4D ZOI for qualified coatings No difference Truncate ZOI at walls Truncate ZOI at walls No difference 4category size distribution for Alion proprietary 4category size Alion 4category size fiberglass debris including fines, distribution methodology distribution methodology small pieces, large pieces, and intact (consistent with guidance in SER previously accepted by NRC for blankets appendices) deterministic evaluations 100% fines for Microtherm debris 100% fines for Microtherm No difference debris 100% fines (10 m) for qualified 100% fines (10 m) for qualified No difference coatings debris coatings debris Public Meeting May 23, 2013 23 DRAFT
DRAFT Topical Area: Debris Generation NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER 100% failure for all unqualified Timedependent and partial New engineering model coatings debris failure of unqualified coatings documented in Volume 3.
based on available data.
Unqualified coatings fail as 10 m Unqualified coatings fail in a size Similar methods previously particles if the strainer is fully distribution based on coating accepted by NRC for covered or as chips if a fiber bed type and available data. deterministic evaluations would not be formed.
Plantspecific walkdowns required to STPspecific walkdown used to No difference determine latent debris quantity determine latent debris quantity Latent debris consists of 85% Latent debris consists of 85% No difference dirt/dust and 15% fiber dirt/dust and 15% fiber Public Meeting May 23, 2013 24 DRAFT
DRAFT Topical Area: Debris Generation 5.a.1) Failure timing, failure amounts, and debris characteristics of unqualified coatings.
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:
Public Meeting May 23, 2013 25 DRAFT
DRAFT Example Response Lower Reactor Total Unqualified Upper Containment Containment Cavity Quantity Coatings Type Quantity (lbm) Quantity Quantity (lbm)
(lbm) (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 Public Meeting May 23, 2013 26 DRAFT
DRAFT Example Response Public Meeting May 23, 2013 27 DRAFT
DRAFT Example Response Time Dependent Time (Hours)
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 Public Meeting May 23, 2013 28 DRAFT
DRAFT Example Response Microscopic Debris Type Debris Size Density Fines: 6 mil particles Fine Chips: 0.0156x15 mil Small Chips: 0.1250.5x15 mil Unqualified Epoxy 124 lbm/ft3 Large Chips: 0.52.0x15 mil Curled Chips: 0.52.0x15 mil Unqualified IOZ Fines: 4 20 m particles 244 lbm/ft3 Unqualified Alkyd Fines: 4 20 m particles 207 lbm/ft3 Unqualified Baked Enamel Fines: 4 20 m particles 93 lbm/ft3 Public Meeting May 23, 2013 29 DRAFT
DRAFT Topical Area: Debris Transport NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER Logic tree approach to analyzing Logic tree approach to analyzing No difference transport phases: blowdown, transport phases: blowdown, washdown, pool fill, washdown, pool fill, recirculation, recirculation, and erosion and erosion All large pieces and a portion of Fines transport proportional to Similar methods previously small pieces are captured when containment flow, grating and accepted by NRC for blowdown flow passes through miscellaneous obstructions capture deterministic evaluations grating. some small and large pieces.
100% washdown of fines, limited 100% washdown of fines. Credit for Includes some new credit for holdup of small holdup of some small piece debris methodology as pieces, and 0% washdown of on concrete floors and grating. 0% documented in Volume 3.
large pieces through grating washdown of large pieces through grating.
Pool fill transport to inactive Pool fill transport to inactive Similar methods previously cavities must be limited to 15% cavities is less than 15%. accepted by NRC for unless sufficient justification can Methodology is based on deterministic evaluations be made exponential equation with uniform mixing of fines.
Public Meeting May 23, 2013 30 DRAFT
DRAFT Topical Area: Debris Transport NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER CFD refinements are appropriate Recirculation transport based on Methodology for CFD for recirculation transport, but a conservative CFD simulations modeling and recirculation blanket assumption that all developed for the deterministic transport analysis debris is uniformly distributed is STP debris transport calculation. previously accepted by NRC not appropriate. All debris was not assumed to be for deterministic uniformly distributed. evaluations.
90% erosion should be used for Probability distribution with a Values are relatively close nontransporting pieces of range of less than 10% erosion to the experimentally unjacketed fiberglass in the based on Alion testing. determined 10% erosion recirculation pool unless value previously accepted additional testing is performed by the NRC for to justify a lower fraction. deterministic evaluations.
1% erosion of small or large 1% erosion of small or large No difference.
pieces of fiberglass held up in pieces of fiberglass held up in upper containment. upper containment.
Minimal previous analysis on Timedependent transport Several aspects of the time timedependent transport. evaluated for pool fill, washdown, dependent transport are recirculation, and erosion. new engineering models as documented in Volume 3.
Public Meeting May 23, 2013 31 DRAFT
DRAFT Topical Area: Debris Transport 5.a.2) Capture of small and large pieces of debris on gratings and obstructions.
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.
Public Meeting May 23, 2013 32 DRAFT
DRAFT Topical Area: Debris Transport 5.a.3) Washdown transport holdups.
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.
Public Meeting May 23, 2013 33 DRAFT
DRAFT Topical Area: Debris Transport 5.a.4) Non-uniform debris distribution at the onset of recirculation.
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.
Public Meeting May 23, 2013 34 DRAFT
DRAFT Topical Area: Debris Transport 5.a.5) Time dependent 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 Public Meeting May 23, 2013 35 DRAFT
DRAFT Topical Area: Chemical Effects NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER Corrosion and dissolution of Corrosion and dissolution of metals Several aspects of the corrosion metals and insulation in and insulation in containment is a and dissolution models are new containment is a function of function of temperature, pH, water engineering models as temperature, pH, and water volume, and pool chemistry. New documented in Volume 3.
volume. Accepted model is model being developed for STP WCAP16530NP. conditions.
100% of material in solution will Some material in solution may not New engineering model precipitate. precipitate depending on the documented in Volume 3.
solubility limit of the precipitate.
Precipitates can be simulated Precipitates are much smaller and New engineering model using the surrogate recipe more benign than WCAP surrogate. documented in Volume 3.
provided in WCAP16530NP.
Public Meeting May 23, 2013 36 DRAFT
DRAFT Topical Area: Chemical Effects 5.a.6) Chemical effects corrosion and dissolution models.
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 Public Meeting May 23, 2013 37 DRAFT
DRAFT Topical Area: Chemical Effects 5.a.7) Basis for excluding any plant materials from chemical testing.
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.
Public Meeting May 23, 2013 38 DRAFT
DRAFT Topical Area: Chemical Effects 5.a.8) Chemical precipitation models - amount, type, head loss effect.
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.
Public Meeting May 23, 2013 39 DRAFT
DRAFT Topical Area: Chemical Effects 5.a.9) Disposition of chemical effects Phenomena Identification and Ranking Table open items.
STP Response:
Methods used to address PIRT issues will be documented with the revised submittal.
Public Meeting May 23, 2013 40 DRAFT
DRAFT Topical Area: Strainer Head Loss NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER Perform plantspecific head loss Modify the NUREG/CR6224 Several aspects of the testing of the bounding correlation to address old ACRS engineering models are new as scenario(s) with a prototype comments and STPspecific conditions documented in Volume 3.
strainer module. so that head loss can be evaluated at the full range of scenarios.
Address chemical effects head Address chemical effects head loss New engineering model loss using WCAP16530NP with a simple bumpup factor similar to documented in Volume 3.
surrogates in prototype strainer the 2011 quantification using the CHLE testing. testing that has been performed so far to justify the conservatism.
Minimum fiber quantity Minimum fiber quantity equivalent to No difference equivalent to 1/16 inch debris 1/16 inch debris bed on the strainers is bed on the strainers is required to required to form a thin bed.
form a thin bed.
Bounding strainer head loss Timedependent strainer head loss Similar engineering model as compared to bounding NPSH compared to timedependent NPSH documented in Volume 3.
margin and bounding structural margin and bounding structural margin margin to determine whether the to determine whether the pumps or pumps or strainer would fail. strainer would fail.
Public Meeting May 23, 2013 41 DRAFT
DRAFT Topical Area: Strainer Head Loss 5.a.10) Head loss model.
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.
Public Meeting May 23, 2013 42 DRAFT
DRAFT Topical Area: Strainer Head Loss 5.a.11) Chemical effects on head loss (bump-up factor) model.
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.
Public Meeting May 23, 2013 43 DRAFT
DRAFT 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)
Public Meeting May 23, 2013 44 DRAFT
DRAFT 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.
Public Meeting May 23, 2013 45 DRAFT
DRAFT Topical Area: Air Intrusion NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER Release of air bubbles at the Release of air bubbles at the strainer No difference strainer calculated based on the calculated based on the water water temperature, temperature, submergence, strainer submergence, strainer head loss, head loss, and flow rate.
and flow rate.
NPSH margin adjusted based on NPSH margin adjusted based on the No difference the void fraction at the pump void fraction at the pump inlet inlet Void fraction at pumps compared Void fraction at pumps compared to a No difference.
to a steadystate void fraction of steadystate void fraction of 2% to 2% to determine whether the determine whether the pumps would pumps would fail. fail.
Public Meeting May 23, 2013 46 DRAFT
DRAFT Topical Area: Debris Penetration NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER Perform plantspecific fiber Develop a fiber penetration correlation New engineering model penetration testing of the as a function of strainer flow rate and documented in Volume 3.
bounding scenario(s) with a fiber accumulation based on a series of prototype strainer module. penetration tests.
100% penetration of 100% penetration of transportable No difference.
transportable particulate and particulate and chemical precipitates.
chemical precipitates.
Public Meeting May 23, 2013 47 DRAFT
DRAFT Topical Area: Debris Penetration 5.a.12) Fiber bypass amounts and amounts reaching the core for various scenarios.
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 Public Meeting May 23, 2013 48 DRAFT
DRAFT Topical Area: Ex-Vessel Downstream Effects NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER Evaluate exvessel wear and Evaluate exvessel wear and clogging No difference.
clogging based on the based on the methodology in WCAP methodology in WCAP16406P 16406P Public Meeting May 23, 2013 49 DRAFT
DRAFT Topical Area: In-Vessel Downstream Effects NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER Compare fiber quantity on core to Use RELAP5 simulations to show that New engineering model bounding 15 g/FA limit based on cold leg SBLOCAs and all hot leg LOCAs documented in Volume 3.
WCAP16793NP. would not go to core damage with full blockage at the base of the core. Use WCAP17057P tests with conditions closer to the STP to justify an appropriate fiber limit on the core.
Evaluate reduced heat transfer Evaluate reduced heat transfer due to No difference.
due to deposition on fuel rods deposition on fuel rods using LOCADM using LOCADM software. software.
Public Meeting May 23, 2013 50 DRAFT
DRAFT Topical Area: In-Vessel Downstream Effects 5.a.13) Fiber limits for in-vessel evaluations.
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 Public Meeting May 23, 2013 51 DRAFT
DRAFT Topical Area: In-Vessel Downstream Effects 5.a.14) Thermal-hydraulic analysis for in-vessel evaluations.
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.
Public Meeting May 23, 2013 52 DRAFT
DRAFT Topical Area: Boron Precipitation NRCApproved Deterministic STP RiskInformed Methods Comparison Methods - NEI 0407 SER No currently accepted Evaluate fiber accumulation on the New engineering model methodology. core for cold leg breaks during cold leg documented in Volume 3.
injection. Assume that 7.5 g/FA of fiber is sufficient to form a debris bed that would prevent natural mixing between the core and lower plenum.
Assume failure due to boron precipitation if this quantity arrives prior to hot leg switchover.
Public Meeting May 23, 2013 53 DRAFT
DRAFT Topical Area: Boron Precipitation 5.a.15) Boric acid precipitation evaluations.
STP Response:
Methodology for addressing boric acid precipitation is described in Volume 3.
Public Meeting May 23, 2013 54 DRAFT
DRAFT Probability Distributions 5.a.16) Methodology for determination and implementation of physical effects 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.
Public Meeting May 23, 2013 55 DRAFT
DRAFT Defense-in-Depth 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.
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.
Public Meeting May 23, 2013 56 DRAFT
DRAFT Defense-in-Depth (DID)
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.
Public Meeting May 23, 2013 57 DRAFT
DRAFT 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.
Public Meeting May 23, 2013 58 DRAFT
DRAFT 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.
Public Meeting May 23, 2013 59 DRAFT
DRAFT 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.
Public Meeting May 23, 2013 60 DRAFT
DRAFT 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 Public Meeting May 23, 2013 61 DRAFT
DRAFT 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.
Public Meeting May 23, 2013 62 DRAFT
DRAFT Barriers for Release of Radioactivity 5.c. Please provide supporting evaluations that demonstrate that the barriers for the release of radioactivity will be maintained with sufficient safety margin.
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.
Public Meeting May 23, 2013 63 DRAFT
DRAFT 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.
Public Meeting May 23, 2013 64 DRAFT
DRAFT Treatment of Uncertainty 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.
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.
Public Meeting May 23, 2013 65 DRAFT
DRAFT Questions and Comments Public Meeting May 23, 2013 66 DRAFT