ML19056A221

NRR E-mail Capture - Brunswick Draft 3rd Round RAI - LAR to Allow Implementation of the Provisions 10 CFR 50.69

ML19056A221
Person / Time
Site:	Brunswick
Issue date:	02/25/2019
From:	Dennis Galvin Plant Licensing Branch II
To:	Zaremba A Duke Energy Carolinas
References
L 2018-LLA-0008
Download: ML19056A221 (6)

Text

NRR-DMPSPEm Resource From: Galvin, Dennis Sent: Monday, February 25, 2019 10:40 AM To: Arthur.Zaremba@duke-energy.com Cc: Vaughan, Jordan L; Grzeck, Lee (Lee.Grzeck@duke-energy.com); Mark Turkal (Mark.Turkal@duke-energy.com); Barillas, Martha; Jordan, Natreon; Shoop, Undine

Subject:

Brunswick Draft 3rd Round RAI - LAR to Allow Implementation of the Provisions 10 CFR 50.69 (EPID L 2018-LLA-0008)

Attachments: Brunswick 50.69 3rd Round Draft RAI L-2018-LLA-0008 2019-02-25.pdf Mr. Zaremba, By letter dated January 10, 2018 (Agencywide Documents Access and Management System Accession No. ML18010A344) as supplemented by letters dated November 2, 2018 (ADAMS Accession No. ML18306A523) and February 13, 2019 (ADAMS Accession No. ML19044A366), Duke Energy Progress, LLC (the licensee) submitted a license amendment request (LAR) for Brunswick Steam Electric Plant Unit Nos. 1 and 2 (Brunswick). The proposed amendment would modify the licensing basis to allow for the implementation of the provisions of Title 10 of the Code of Federal Regulations (10 CFR), Section 50.69, Risk-informed categorization and treatment of structures, systems, and components for nuclear power plants, and provide the ability to use probabilistic risk assessment (PRA) models, namely the internal events PRA, internal flooding PRA (IFPRA), internal fire PRA (FPRA), high winds PRA (HW PRA), and external flooding PRA (XF PRA) for the proposed 10 CFR 50.69 categorization process.

To complete its review, the NRC staff has prepared the attached 3nd round requests for additional information (RAIs) in DRAFT form. To arrange a clarification call for the attached draft RAIs and to discuss the due date for the RAI responses, please contact me at (301) 415-6256. Note that the NRC staff has closely related RAIs for the Shearon Harris Nuclear Power Plant, Unit 1 (Harris) and the H. B. Robinson Steam Electric Plant, Unit 2 (Robinson), and anticipates that one clarification call can be held for the RAIs.

Respectfully, Dennis Galvin Project Manager U.S Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of Operating Reactor Licensing Licensing Project Branch 2-2 301-415-6256 Docket No. 50-325, 50-324 1

Hearing Identifier: NRR_DMPS Email Number: 816 Mail Envelope Properties (Dennis.Galvin@nrc.gov20190225104000)

Subject:

Brunswick Draft 3rd Round RAI - LAR to Allow Implementation of the Provisions 10 CFR 50.69 (EPID L 2018-LLA-0008)

Sent Date: 2/25/2019 10:40:14 AM Received Date: 2/25/2019 10:40:00 AM From: Galvin, Dennis Created By: Dennis.Galvin@nrc.gov Recipients:

"Vaughan, Jordan L" <Jordan.Vaughan@duke-energy.com>

Tracking Status: None "Grzeck, Lee (Lee.Grzeck@duke-energy.com)" <Lee.Grzeck@duke-energy.com>

Tracking Status: None "Mark Turkal (Mark.Turkal@duke-energy.com)" <Mark.Turkal@duke-energy.com>

Tracking Status: None "Barillas, Martha" <Martha.Barillas@nrc.gov>

Tracking Status: None "Jordan, Natreon" <Natreon.Jordan@nrc.gov>

Tracking Status: None "Shoop, Undine" <Undine.Shoop@nrc.gov>

Tracking Status: None "Arthur.Zaremba@duke-energy.com" <Arthur.Zaremba@duke-energy.com>

Tracking Status: None Post Office:

Files Size Date & Time MESSAGE 1762 2/25/2019 10:40:00 AM Brunswick 50.69 3rd Round Draft RAI L-2018-LLA-0008 2019-02-25.pdf 142882 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

Recipients Received:

DRAFT REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING LICENSE AMENDMENT REQUEST TO ADOPT 10 CFR 50.69 RISK-INFORMED CATEGORIZATION OF STRUCTURES, SYSTEMS, AND COMPONENTS DUKE ENERGY PROGRESS, LLC BRUNSWICK STEAM ELECTRIC PLANT, UNITS 1 AND 2 DOCKET NOS. 50-325 AND 50-324 By letter dated January 10, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18010A344), as supplemented by letters dated November 2, 2018 (ADAMS Accession No. ML18306A523) and February 13, 2019 (ADAMS Accession No. ML19044A366), Duke Energy Progress, LLC (the licensee) submitted a license amendment request (LAR) regarding the Brunswick Steam Electric Plant, Units 1 and 2 (Brunswick). The licensee proposed to add a new license condition to the Renewed Facility Operating Licenses to allow the implementation of Title 10 of the Code of Federal Regulations (10 CFR) Section 50.69, Risk-informed categorization and treatment of structures, systems and components for nuclear power reactors. The provisions of 10 CFR 50.69 allow adjustment of the scope of structures, systems, and components (SSCs) subject to special treatment requirements (e.g., quality assurance, testing, inspection, condition monitoring, assessment, and evaluation) based on a method of categorizing SSCs according to their safety significance. The NRC staff has identified the need for additional information to complete its review.

Regulatory Basis Nuclear Energy Institute (NEI) 00-04, Revision 0, 10 CFR 50.69 SSC Categorization Guideline (ADAMS Accession No. ML052910035), describes a process for determining the safety-significance of SSCs and categorizing them into the four RISC categories defined in 10 CFR 50.69. This categorization process is an integrated decision-making process that incorporates risk and traditional engineering insights.

NUREG-1855, Revision 1, Guidelines on the Treatment of Uncertainties Associated with PRAs in Risk-Informed Decision Making (ADAMS Accession No. ML17062A466), provides guidance on how to treat uncertainties associated with probabilistic risk assessment (PRA) in risk-informed decision-making.

Regulatory Guide (RG) 1.200, Revision 2 An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk Informed Activities (ADAMS Accession No. ML090410014) describes an acceptable approach for determining whether the quality of the PRA, in total or the parts that are used to support an application, is sufficient to provide confidence in the results, such that the PRA can be used in regulatory decision making for light-water reactors. It endorses, with clarifications, the American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) PRA Standard ASME/ANS RA-Sa-2009 (ASME/ANS 2009 Standard or PRA Standard) (ADAMS Accession No. ML092870592).

DRAFT

DRAFT 2

RAI 4.01/17.01 The January 10, 2018, LAR states:

The process to categorize each system will be consistent with the guidance in NEI 00-04, 10 CFR 50.69 SSC Categorization Guideline, as endorsed by RG 1.201. RG 1.201 states that the implementation of all processes described in NEI 00-04 (i.e., Sections 2 through 12) is integral to providing reasonable confidence and that all aspects of NEI 00-04 must be followed to achieve reasonable confidence in the evaluations required by

§50.69(c)(1)(iv).

NEI 00-04 references RG 1.200 as the primary basis for evaluating the technical adequacy of the PRA. RG 1.200 references the ASME/ANS RA-Sa-2009 Standard that requires the identification and documentation of assumptions and source of uncertainty during a peer review.

RG 1.200 also references NUREG-1855 as one acceptable means to identify key assumptions and key sources of uncertainty. RG 1.200, Rev. 2 defines a key uncertainty as one that is related to an issue in which there is no consensus approach or model and where the choice of the approach or model is known to have an impact on the risk profile such that it influences a decision being made using the PRA. RG 1.200, Rev. 2 defines a key assumption as one that is made in response to a key source of modeling uncertainty in the knowledge that a different reasonable alternative assumption would produce different results. The term reasonable alternative is also defined in RG 1.200, Rev. 2.

RAIs 4 and 17 requested the licensee discuss how key assumptions and (key) uncertainties that could impact the results are identified and included in the evaluation. In the responses to RAIs 4 and 17 in the letter dated November 2, 2018, the licensee refers to the integrated risk sensitivity as described in Section 8 of NEI 00-04. For this integrated risk sensitivity study, the unreliability of all low safety significant (LSS) structures, systems, and components (SSCs) is increased by a factor of three (consistent with NEI 00-04) and the subsequent total risk increase is compared to the RG 1.174, An Approach for Using Probabilistic Risk Assessment In Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (ADAMS Accession No. ML17317A256) acceptable risk increase guidelines. The licensee stated that this integrated risk sensitivity study, and the subsequent performance monitoring of LSS SSCs, could be used directly to address the assumptions and sources of uncertainty instead of identifying and evaluating key assumptions and key uncertainties as described in NUREG-1855. The response to RAI 4 also included a table titled Uncertainties and assumptions not addressed by 10 CFR 50.69 factor of 3 sensitivity/performance monitoring with 32 entries. The licensee recognized that assumptions and uncertainties that cause SSCs to be excluded from the PRA cannot be addressed by the integrated risk sensitivity. The entries in the Table are apparently identified and included because they cause SSCs to be excluded. The dispositions in the Table include dispositions consistent with the NUREG-1855 options of (1) refining the PRA if needed, (2) redefine the application (e.g., add a sensitivity study), or (3) add compensatory measure and monitoring specific to that assumption of uncertainty. However, the title of the table implies that all the unreported assumptions and uncertainty are evaluated and dispositioned as not being key solely using the factor of 3. Furthermore, most dispositions included in the Table also include the phrase [a]ny impact of the exclusion of these scenarios on acceptance criteria for categorizations of other components is addressed by the factor of 3 sensitivity and performance monitoring.

The NRC staff finds that the licensees proposed method is a deviation from the guidance of NEI 00-04 and NUREG-1855, Revision 1 for the following reasons. Figure 1-2 in Section 1.5, DRAFT

DRAFT 3

Categorization Process Summary, of NEI 00-04 illustrates the available paths through the accepted categorization process. The categorization provides the appropriate LSS/HSS category. The integrated risk sensitivity study is only performed after all steps in the categorization have been completed and it is not intended to be a change in the risk estimate.

The study simply verifies that the combined impact of any postulated simultaneous degradation in reliability of all LSS SSCs would not result in a significant increases in core damage frequency (CDF) and large early release frequency (LERF). Therefore, the aggregate risk sensitivity study is intended to capture the uncertainty from relaxation of special treatment for candidate LSS SSCs. Other assumptions and uncertainties are related to models and methods used in the PRA and the impact of these assumptions and uncertainties is not considered or included in the integrated risk sensitivity study.

NUREG-1855 identifies that one key source of uncertainty is the unknown increase in unreliability associated with the reduced special treatment requirements on LSS SSCs allowed by 10 CFR 50.69. The NUREG states that one acceptable technique to address this specific key source of uncertainty is to increase the unreliability of LSS SSCs by a multiplicative factor in an integrated risk sensitivity study. NEI 00-04 discusses using a factor of 3 to 5 as an acceptable multiplicative factor to address this uncertainty and the licensee selected to use the factor of 3. In contrast, addressing key assumptions and key sources of uncertainty in the PRA might require that SSCs be added to the PRA, might require changes to the model logic, or might require changes in the unreliability (e.g., unreliability increases for unusual uses of SSCs and for consequential failures) greater than the factor of 3 used in the integrated risk sensitivity study. Even for components that are modeled, the integrated risk sensitivity study only addresses the impact of SSCs as they are included in the PRA logic models without addressing any changes to the logic model itself that might be needed to address the key assumption (i.e.,

because of limitations in scope or level of detail). Further, the licensees proposed approach of changing only the random failure probabilities does not provide any basis or justification for how the proposed approach captures the impact of key modeling assumptions and sources of uncertainty related to external hazard specific failure modes (e.g. tornado missile impact failure probability). In addition, the use of the integrated risk sensitivity will result in the licensee identifying potential categorization of a LSS SSC as HSS only if the RG 1.174 risk acceptance guidelines are exceeded. However, addressing key assumptions and source of uncertainty, can result in a change in categorization even if the RG 1.174 guidelines are not exceeded. NEI 00-04 guidance in Tables 5-2 through 5-5 recognizes such occurrences and Figure 7-2 in NEI 00-04, Example Risk-Informed SSC Assessment Worksheet, captures such a change in categorization due to the sensitivity studies recommended in Tables 5-2 through 5-5.

The licensees response simply states and does not justify that the use of the factors in the integrated risk sensitivity study are sufficient to capture the impact of all assumptions and uncertainties on the categorization of SSCs modeled in the current PRA. The approach proposed by the licensee represents a substantial deviation from the endorsed guidance for categorization in NEI 00-04 and the RAI response does not provide sufficient justification for the appropriateness of the deviation. It is unclear to the NRC staff whether the evaluation of assumptions and uncertainties proposed by the licensee can determine the effect of the key assumptions and uncertainties on the categorization of an indeterminate number of components. Therefore, the staff is unable to conclude that the components placed in LSS accurately reflect the approved risk-informed process. Based on the above, provide the following information:

a. Clarify which process is used and is meant by the RAI 4 Table title, Uncertainties and Assumptions Not Addressed by 10 CFR 50.69 Factor of 3 Sensitivity/Performance DRAFT

DRAFT 4

Monitoring, i.e., which types of uncertainties and assumptions have been addressed by the factor of three.

b. Describe the approach used to identify the assumptions and uncertainties that are used in each of the base PRA models supporting the categorization as stated in the LAR. The descriptions should be provided separately for internal hazard PRAs (including internal fire) and external hazard PRAs supporting this application.

c. Describe the approach(s) used to evaluate each assumption and uncertainty to determine whether each assumption and uncertainty is key or not for this application.

The descriptions should be provided separately for internal hazard PRAs (including internal fire) and external hazard PRAs supporting this application.

d. Provide a summary of the different types of dispositions used for those assumptions and uncertainties determined not to be key for this application. The summaries should be provided separately for internal hazard PRAs (including internal fire) and external hazard PRAs supporting this application.

e. Provide a summary list of the key assumptions and uncertainties that have been identified for the application, and discuss how each identified key assumption and uncertainty will be dispositioned in the categorization process. The discussion should clarify whether the licensee is following NEI 00-04 guidance by performing sensitivity analysis or other accepted guidance such as NUREG-1855 Stages A and F. The summaries and descriptions should be provided separately for the identified key assumptions and uncertainties related to internal hazard PRAs (including internal fire) and those related to external hazard PRAs supporting this application.

f. If NEI 00-04 or NUREG-1855 guidance is not used (e.g. all of the Stages A through F in NUREG 1855, Revision 1) provide justification that the licensees approach is adequate to identify, capture the impact, and disposition key assumptions and uncertainties to support the categorization process. The justification should be provided separately for key assumptions and uncertainties related to internal hazard PRAs (including internal fire) and those related to external hazard PRAs supporting this application.

DRAFT