ML19183A012

Response to Request for Additional Information Regarding the Application to Adopt 10 CFR 50.69, Risk-informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power ...

ML19183A012
Person / Time
Site:	Calvert Cliffs
Issue date:	07/01/2019
From:	Jim Barstow Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EPID L-2018-LIA-0482
Download: ML19183A012 (10)

Text

Exelon Generation 200 Exelon Way Kennett Square. PA 19348 www.exeloncorp.com 10 CFR 50.90 10 CFR 50.69 July 1, 2019 U.S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, DC 20555-0001 Calvert Cliffs Nuclear Power Plant, Units 1 and 2 Renewed Facility Operating License Nos. DPR-53 and DPR-69 Docket Nos. 50-317 and 50-318

Subject:

Response to Request for Additional Information Regarding the Application to Adopt 1O CFR 50.69, "Risk-informed categorization and treatment of structures, systems, and components for nuclear power reactors".

References:

1) License Amendment Request dated November 28, 2018 titled "Application to Adopt 1O CFR 50.69, Risk-informed categorization and treatment of structures, systems, and components for nuclear power reactors."

2) Supplement to Application to Adopt 1O CFR 50.69, "Risk-informed categorization and treatment of structures, systems, and components for nuclear power reactors," dated November 29, 2018.

3) Revised submittal to Application to Adopt 1O CFR 50.69, "Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Reactors," dated May 10, 2019.

4) E-mail from Michael Marshall, U.S. Nuclear Regulatory Commission, to Enrique Villar, Exelon, titled "[External] Calvert Cliffs Nuclear Power Plant, Units 1 and 2 - Request for Additional Information Regarding Request to Adopt 1O CFR 50.69 Risk Informed Categorization and Treatment of Systems, Structures, and Components (EPID L-2018-LIA-0482)," dated June 4, 2019. (ML19155A127).

By letter dated November 28, 2018 (Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML18333A022), as supplemented by letters dated November 29, 2018 and May 10, 2019 (ADAMS Accession Nos. ML18337A038 and ML19130A180, respectively), Exelon Generation Company, LLC (Exelon) submitted a license amendment request (LAR) regarding Calvert Cliffs Nuclear Power Plant Units 1 and 2 (CCNPP). 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),

Part 50.69, "Risk-Informed Categorization and Treatment of Structures, Systems, and Components (SSCs) for Nuclear Power Reactors."

Response to Request for Additional Information Application to Adopt 10 CFR 50.69 July 1, 2019 Page2 to this letter contains Exelon's 30-day response to RAls 4, 5, 6, and 8. Exelon has reviewed the information supporting a finding of no significant hazards consideration, and the environmental consideration, that were previously provided to the NRC in Reference 1 letter. Exelon has concluded that the information provided in this response does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration under the standards set forth in 1O CFR 50.92.

In addition, Exelon has concluded that the information in this response does not affect the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.

There are no regulatory commitments contained in this letter.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 1st day of July 2019.

If you should have any questions regarding this submittal, please contact Enrique Villar at 610-765-5736.

James Barstow Director - Licensing and Regulatory Affairs Exelon Generation Company, LLC

Attachment:

1) Response to Request for Additional Information to License Amendment Request to Adopt 1O CFR 50.69 cc: Regional Administrator, NRC Region I NRC Senior Resident Inspector NRC Project Manager D. A. Tancabel, State of Maryland

ATTACHMENT 1 Response to Request for Additional Information Nos 4, 5, 6, and 8 in Support to License Amendment Request to Adopt 10 CFR 50.69

Response to Request for Additional Information Nos 4, 5, 6, and 8 in Support to License Amendment Request to Adopt 10 CFR 50.69 July 1, 2019 Page 1 of 7 REQUESTS FOR ADDITIONAL INFORMATION

4. Section 3.2.3 of Attachment 1 to the letter dated May 10, 2019 includes a discussion of the consideration of seismic events for SSCs that are HSS uniquely from a PRA model but not from the integrated importance measure assessment. The discussion in the first paragraph on Page 16 of Attachment 1states:

For HSS SSCs uniquely identified by the CCNPP PAA models but having design-basis functions during seismic events or functions credited for mitigation and prevention of severe accidents caused by seismic events, these will be addressed using non-PRA based qualitative assessments in conjunction with any seismic insights provided by the PRA.

In the letter dated November 28, 2018, Exelon proposed to use an internal events PRA and a Fire PAA for its 1O CFR 50.69 categorization at Calvert Cliffs. The guidance in NEI 00-04 states that HSS SSCs from identified from the internal events PRA remain HSS and the IDP cannot change such SSCs to LSS. The guidance is also reflected in Table 3-1 in Attachment 1 to the supplement. Therefore, only the Fire PRA model appears to be relevant to the discussion about consideration of seismic events for SSCs that are HSS uniquely from a PRA model but not from the integrated importance measure assessment.

However, the third paragraph on Page 16 Attachment 1 to the letter dated May 10, 2019, specifically identifies the consideration of seismic events for SSCs that are HSS from the Fire PAA but not HSS from internal events PRA and states that, for such SSCs:

[ ... ]the categorization team will review design-basis functions during seismic events or functions credited for mitigation and prevention of severe accidents caused by seismic events and characterize these for presentation to the IDP as additional qualitative inputs [ ... ]

It appears that the discussion in Section 3.2.3 of Attachment 1 to the supplement provides seemingly different approaches for the consideration of seismic events for SSCs that are HSS from the Fire PAA which are not HSS from the internal events PRA (i.e., SSCs that are uniquely HSS from a fire PRA model but not from the integrated importance measure assessment). The approach described in the first paragraph on Page 16 involves "using non-PRA based qualitative assessments in conjunction with any seismic insights provided by the PRA". The other approach described in the second paragraph on Page 16 involves "review[ ... ] and characterize these for presentation to the IDP as additional qualitative inputs". It is unclear which approach is being proposed for such SSCs.

a. Clarify the approach for the consideration of seismic events for SSCs that are HSS from the Fire PRA which are not HSS from the internal events PAA (i.e., SSCs that are uniquely HSS from a fire PRA model but not from the integrated importance measure assessment). The clarification should reconcile the seemingly different approaches noted above.

Response to Request for Additional Information Nos 4, 5, 6, and 8 in Support to License Amendment Request to Adopt 10 CFR 50.69 July 1, 2019 Page 2 of 7

b. If the approach includes the use of "seismic insights provided by the PAA", clarify how such insights will be developed given that Exelon does not have a seismic PAA for Calvert Cliffs that meets the guidance in RG 1.200.

Exelon Response RAl4.a The following clarifies the intent of the two paragraphs cited in the question.

The approach accounting for seismic considerations for SSC(s) in the system being categorized that are uniquely HSS from the fire PAA but not from the integrated importance measure assessment will involve a review by the categorization team. The categorization team will review the design-basis functions of the SSC(s) during seismic events or functions credited for mitigation and prevention of severe accidents caused by seismic events. The team will present the results of these reviews to the Integrated Decision-making Panel and describe them in the System Categorization Document.

RAI 4.b As stated in part b of the RAI, Calvert Cliffs does not have a seismic PAA that meets the guidance in RG 1.200.

As discussed in the supplemental letter (Reference 3), the insights will be developed by the review of appropriate seismic information from available Calvert Cliffs seismic evaluations, such as those listed in Section 3.2.3 of the supplement. This information will be reviewed and discussed with the IDP. The review and discussion will focus on those SSCs that are HSS from the fire PAA, because such SSCs may not end up being HSS from the PAA integrated importance assessment.

Response to Request for Additional Information Nos 4, 5, 6, and 8 in Support to License Amendment Request to Adopt 10 CFR 50.69 July 1, 2019 Page 3 of 7

5. NEI 00-04 provides guidance on including external events in the categorization of each SSC to be categorized. The process begins with the SSC selected for categorization, as illustrated in NEI 00-04, Section 5.4, Figure 5-6, and proceeds through the flow logic for each external hazard. According to Figure 5-6, if a component participates in a screened scenario, then for that component to be considered candidate LSS, it has to be further shown that if the component was removed, the screened scenario would not become unscreened.

LAR Section 3.2.4 indicates that all other hazards were screened from applicability to Calvert Cliffs per a plant-specific evaluation in accordance with the criteria in Part 6 of the ASME/ANS PRA Standard RA-SA-2009. This statement appears to indicate that the licensee proposes to treat all SSCs as LSS with respect to other external events risk.

The LAR provides no further explanation of how the risk for other external hazards will be considered in the 1O CFR 50.69 categorization (i.e., components being categorized that participate in screened scenarios and whose failure would result in an unscreened scenario). LAR Attachments 4 and 5 provide a summary of the other external hazards screening results, but do not appear to address any considerations related to applying Figure 5-6 of NEI 00-04.

Confirm that any SSCs credited for screening of external hazards will be evaluated according to the flow chart in NEI 00-04, Figure 5-6 during the implementation of the categorization process at Calvert Cliffs, or otherwise provide technical and regulatory justification for your proposed approach.

Exelon Response SSCs credited for screening of external hazards will be evaluated according to the flow chart in NEI 00-04, Figure 5-6.

Response to Request for Additional Information Nos 4, 5, 6, and 8 in Support to License Amendment Request to Adopt 10 CFR 50.69 July 1, 2019 Page 4 of 7

6. Section 69(c)(v) of 1O CFR 50 requires that the categorization be performed for entire systems and structures - not for selected components within a system or structure.

NEI 00-04, Section 7.1 states:

[d]ue to the overlap of functions and components, a significant number of components support multiple functions. In this case, the SSC or part thereof should be assigned the highest risk significance for any function that the SSC or part thereof supports.

Section 4 of NEI 00-04 also states that a candidate LSS SSC that supports an interfacing system "will remain uncategorized until the interfacing system is considered". It further concludes "[t]herefore the SSC will remain uncategorized and continue to receive its current level of treatment requirements".

The LAA does not discuss consideration or implementation of the guidance in Section 7.1 of NEI 00-04.

NEI 00-04 Section 4 provides the following example that highlights the categorization process that involve SSCs which support interfacing systems: "... cooling water piping on a ventilation system cooler is designated as part of the ventilation system. The impact of failure of the SSC on the ventilation system can be considered, but the impact of failure of the SSC on the cooling water system cannot be fully assessed until that system is considered as part of the future categorization process. Therefore, the SSC will remain uncategorized and continue to receive its current level of treatment requirements".

Consistent with 1O CFR 50.69(c)(v) requiring that the categorization be performed for entire systems and structures, the NRC staff interprets the NEI 00-04 guidance that interfacing functions/SSCs cannot be categorized and be subject to alternative treatment until the categorization of all the systems that they support is completed. Further, the SSCs supporting multiple functions will be assigned the highest risk significance for any of the functions they support.

Confirm that in the Calvert Cliffs categorization process, any functions/SSCs that serve as an interface between two or more systems will not be categorized and will not receive alternative treatment prior to completing the categorization for all of the systems that they support. Alternatively, describe and provide detailed technical and regulatory justification for your proposed approach.

Response to Request for Additional Information Nos 4, 5, 6, and 8 in Support to License Amendment Request to Adopt 10 CFR 50.69 July 1, 2019 Page 5 of 7 Exelon Response Exelon will perform the categorization of any functions/SSCs that serve as an interface between two or more systems in accordance with its categorization procedures.

If an interface component is found to be HSS for the system being categorized, then it will be categorized RISC-1 or RISC-2 (and will not receive alternative treatments) even if it supports other systems.

In most cases, interface components that support uncategorized interfacing systems (and are LSS for the system being categorized) will be uncategorized and will not receive alternative treatment prior to completing the categorization of all systems that they support.

One of the initial steps in the Exelon's system categorization procedure is to develop a list of system functions. If the system includes components that support functions of other systems, then support functions are created to identify the supported systems (e.g., provide support for system xx) as needed.

Support functions are not categorized. These functions identify system components that cannot be fully categorized until the categorization of other systems is completed. Additional support functions are added as required during the component mapping process, where the focus is on individual component functions. Interface components that support other system functions will be identified by this process.

In some cases, impacts that an interfacing component could have on an interfacing system can be fully determined and the interface component can be categorized (and alternative treatment implemented) without categorizing the entire interfacing system.

In this event, an assessment of interface component risk associated with uncategorized systems will be limited to:

1. cases where an interface component failure cannot prevent performance of interface system functions, or

2. the risk is limited to passive failures assessed as low safety-significant following the passive categorization process for the applicable pressure boundary segments.

In either case, the component can be assessed without performing a full interface system categorization because adequate interface system function knowledge is available to perform the functional assessment and passive risk assessment. Categorizing the entire interfacing system would produce the same functional assessment and passive risk significance for the component. Therefore, Exelon considers this approach to be consistent with the intent of 10 CFR 50.69(c)(1 )(v) and NEI 00-04 guidance.

Response to Request for Additional Information Nos 4, 5, 6, and 8 in Support to License Amendment Request to Adopt 10 CFR 50.69 July 1, 2019 Page 6 of 7

8. The NRC memorandum dated May 30, 2017, "Assessment of the NEI 16-06, 'Crediting Mitigating Strategies in Risk-Informed Decision Making,' Guidance for Risk-Informed Changes to Plants Licensing Basis" (ADAMS Accession No. ML17031A269), provides the NRC's staff assessment of identified differences between NEI 16-06 guidance and the guidance in RG 1.200 Revision 2 for incorporating diverse and flexible coping strategies and equipment into a PAA model in support of risk-informed decision making. It is unclear whether the licensee's FPIE and/or Fire PAA used to support this application credits FLEX equipment and operator actions. For the NAC staff to determine the acceptability of incorporation of FLEX equipment into the PAA model(s) provide the following:

a. Confirm whether FLEX equipment and associated operator actions have been credited in the FPIE and/or Fire PAA. If no FLEX credit is applied in the FPIE and/or Fire PAA, the remaining questions for this AAI do not apply.

b. If FLEX equipment or operator actions have been credited in the PAA, address the following, separately for FPIE (includes internal flooding), Fire PAA and external hazards screening as appropriate:

i. Summarize the supplemental equipment and compensatory actions, including FLEX strategies that have been quantitatively credited for each of the PAA models used to support this application. Include discussion of whether the credited FLEX equipment is portable or permanently installed equipment.

ii. Discuss whether the credited equipment (regardless of whether it is portable or permanently-installed) are similar to other plant equipment (i.e., SSCs with sufficient plant-specific or generic industry data) and whether credited operators actions are similar to other operator actions evaluated using approaches consistent with the endorsed ASME/ANS RA-Sa-2009 PAA Standard.

iii. If any credited FLEX equipment is dissimilar to other plant equipment credited in the PAA (i.e., SSCs with sufficient plant-specific or generic industry data),

discuss the data and failure probabilities used to support the modeling and provide the rationale for using the chosen data. Discuss whether the uncertainties associated with the parameter values are in accordance with the ASME/ANS PAA Standard as endorsed by RG 1.200 Revision 2.

iv. If any operator actions related to FLEX equipment are evaluated using approaches that are not consistent with the endorsed ASME/ANS RA-Sa-2009 PAA Standard (e.g., using surrogates), discuss the methodology used to assess human error probabilities for these operator actions. The discussion should include:

Response to Request for Additional Information Nos 4, 5, 6, and 8 in Support to License Amendment Request to Adopt 10 CFR 50.69 July 1, 2019 Page 7 of 7

1. A summary of how the impact of the plant-specific human error probabilities and associated scenario-specific performance shaping factors listed in (a)-U) of supporting requirement HR-G3 of the ASME/ANS RA-Sa-2009 PAA Standard were evaluated.

2. Whether maintenance procedures for the portable equipment were reviewed for possible pre-initiator human failures that renders the equipment unavailable during an event, and if the probabilities of the pre-initiator human failure events were assessed as described in HLR-HR-D of the ASME/ANS RA-Sa-2009 PAA Standard.

3. If the procedures governing the initiation or entry into mitigating strategies are ambiguous, vague, or not explicit, a discussion detailing the technical bases for probability of failure to initiate mitigating strategies.

v. The ASME/ANS RA-Sa-2009 PAA standard defines PAA upgrade as the incorporation into a PAA model of a new methodology or significant changes in scope or capability that impact the significant accident sequences or the significant accident progression sequences. Section 1-5 of Part 1 of ASME/ANS RA-Sa-2009 PAA Standard states that upgrades of a PAA shall receive a peer review in accordance with the requirements specified in the peer review section of each respective part of this Standard.

Provide an evaluation of the model changes associated with incorporating mitigating strategies, which demonstrates that none of the following criteria is satisfied: (1) use of new methodology, (2) change in scope that impacts the significant accident sequences or the significant accident progression sequences, and (3) change in capability that impacts the significant accident sequences or the significant accident progression sequences.

Exelon Response RAIS.a FLEX equipment and associated operator actions are not currently credited in the Calvert FPIE and/or Fire PAA. If FLEX equipment and associated operator actions are credited in the future, then that incorporation will be done per the NRG-endorsed version of the ASME/ANS PAA standard in accordance with the latest revision of NRC Regulatory Guide 1.200.

RAI 8.b (all parts)

See part a.