ML17261A078

Request for Additional Information Regarding Relief Request I4R-01 (CAC Nos. MF9758 and MF9759; EPID L-2017-LLR-0057)

ML17261A078
Person / Time
Site:	LaSalle
Issue date:	10/12/2017
From:	Bhalchandra Vaidya Plant Licensing Branch III
To:	Bryan Hanson Exelon Generation Co, Exelon Nuclear
Vaidya B, NRR/DORL/LPLIII, 415-3308
References
CAC MF9758, CAC MF9759, EPID L-2017-LLR-0057
Download: ML17261A078 (7)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 October 12, 2017 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer (CNO)

Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

LASALLE COUNTY STATION, UNITS 1 AND 2, REQUEST FOR ADDITIONAL INFORMATION REGARDING RELIEF REQUEST 14R-01, REQUESTS APPROVAL OF ALTERNATIVE RISK-INFORMED INSERVICE INSPECTION INTERVAL PROGRAM AND EXAMINATION CRITERIA FOR EXAMINATION CATEGORY 8-F, 8-J, C-F-1, AND C-F-2 PRESSURE RETAINING PIPING WELDS IN ACCORDANCE WITH ASME CODE CASE N-578-1, "RISK-INFORMED REQUIREMENTS FOR CLASS 1, 2, OR 3 PIPING, METHOD B, SECTION XI, DIVISION 1." (CAC NOS. MF9758 AND MF9759; EPID L-2017-LLR-0057)

Dear Mr. Hanson:

By letter dated May 30, 2017, as supplemented by letter dated July 20, 2017 (Agencywide Documents Access management System (ADAMS) Accession Nos. ML17150A449 and ML17201Q396, respectively), Exelon Generation Company, LLC (the licensee) submitted relief request 14R-01, Requests Approval Of Alternative Risk-Informed lsi Program And Examination Criteria For Examination Category 8-F, 8-J, C-F-1, and C-F-2 Pressure Retaining Piping Welds In Accordance With ASME Code Case N-578-1, "Risk-Informed Requirements For Class 1, 2, or 3 Piping, Method B, Section Xi, Division 1," for the LaSalle County Station, Units 1 and 2.

The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure to this letter. During the telephone discussion between the NRC staff and the licensee on October 11, 2017, for clarification of these requests for additional information (RAls), it was agreed that the licensee will provide the responses to these RAls no later than close of business on November 13, 2017.

The NRC staff considers that timely responses to these RAls help ensure sufficient time is available for NRC staff review and contribute toward the NRC's goal of efficient and effective use of staff resources.

B. Hanson If you have any questions, please call me at 301-415-3308.

Sincerely,

~~

Bhalchandra Vaidya, Project Manager Plant Licensing Branch Ill Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-373 and 50-37 4

Enclosure:

Request for Additional Information cc w/encl: Distribution via ListServ

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 REQUEST FOR ADDITIONAL INFORMATION REGARDING RELIEF REQUEST 14R-01, REQUESTS APPROVAL OF ALTERNATIVE RISK-INFORMED INSERVICE INSPECTION INTERVAL PROGRAM AND EXAMINATION CRITERIA FOR EXAMINATION CATEGORY 8-F, 8-J, C-F-1, AND C-F-2 PRESSURE RETAINING PIPING WELDS IN ACCORDANCE WITH ASME CODE CASE N-578-1, "RISK-INFORMED REQUIREMENTS FOR CLASS 1, 2, OR 3 PIPING, METHOD B, SECTION XI, DIVISION 1."

LA SALLE COUNTY STATION, UNITS 1 AND 2 (CAC NOS. MF9758 AND MF9759)

By letter dated May 30, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML17150A449), as supplemented by letter dated July 20, 2017 (ADAMS ML17201Q396), Exelon Generation Company, LLC (the licensee), submitted its fourth 10-year inservice inspection (ISi) interval program relief requests for LaSalle County Station, Units 1 and 2. In accordance with Title 10 of the Code of Federal Regulations (1 O CFR),

Section 50.55a(z)(1 ), the licensee is requesting relief on the basis that the proposed alternative utilizing Electric Power Research Institute (EPRI) Topical Report 112657, "Revised Risk-Informed In-service Inspection Evaluation Procedure," Revision B-A (ADAMS No.

ML013470102), along with two enhancements from the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Case N-578-1, "Risk-Informed Requirements for Class 1, 2, or 3 Piping, Method B,Section XI," will provide an acceptable level of quality and safety. To complete this review, the U.S. Nuclear Regulatory Commission (NRC) staff requests responses to the following questions:

Probabilistic Risk Assessment (PRA) Request for Additional Information (RAI) 1- Logic Model Enhancement identified as PRA Maintenance In the letter dated July 20, 2017, (ADAMS No. ML172010396), the licensee identified four changes to the PRA model as shown below. The licensee classified each change as PRA maintenance rather than a PRA upgrade with respect to the definitions provided in American Society of Mechanical Engineers /American Nuclear Society RA-Sa-2009, "Addenda to ASME RA-S-2008 Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications" (the PRA Standard). In order for the NRC staff to confirm that the changes qualified as maintenance as opposed to upgrades, provide the following:

I. 2011 PRA Model Change, "Deleted loss of bus 241 Y and 242Y as initiating events and added loss of bus 241X, 242X and 251 as initiating events."

According to Section 1-A.3.5 of the PRA Standard, replacement of point estimates with system fault trees for support system initiators constitutes an upgrade, although Enclosure

this may be permitted as maintenance rather than upgrade if the contribution is not risk significant:

Discuss whether the added initiating events were incorporated as point estimates or fault trees. If any were fault trees:

a. Discuss whether the initiator frequencies rose or fell bafter the incorporation of the fault trees and, if they did rise, describe whether they were risk-significant and provide an explanation of this fluctuation.

b. Discuss whether any potential interactions with other systems were included in the PRA model (e.g., interactions to ensure that any common cause failures have been addressed) and provide details of these interactions.

II. 2011 PRA Model Change, "Created a new event tree for isolated Turbine Building and Auxiliary Building floods."

Provide the justification for citing the impact of this new event as "small."

Ill. 2011 PRA Model Change, "Converted the Human Reliability Analysis (HRA) Calculations to the EPRI HRA Calculator," software platform. The HRA Calculator was also used to facilitate the human error probability (HEP) dependence analysis.

a. In adopting the HRA Calculator, describe whether the exact same methods, steps, and sequence that were used in the pre-existing manual HRA calculations, were exactly mirrored when adopting the HRA Calculator (e.g., Human Cognitive Reliability (HCR)/Operator Reliability Experiments (ORE) Method for the diagnostic phase and Technique For Human Error Rate Prediction (THERP) for the execution phase).

b. Describe whether the independent review of the HRA was performed by an analyst experienced in HRA Calculations who is not a licensee employee or a contractor involved in the incorporation of the HRA Calculator, and provide a description of the analyst's professional profile.

IV. 2011 PRA Model Change, "The fault trees related to recovery of AC [alternating current]

power in the intermediate timeframe were enhanced by modifying the gate names and descriptors to clarify that the intermediate timeframe is 2 to 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />. Also, the conditional probability that the battery fails was changed and was or'ed [OR Gated] with the operator action to load shed."

a. Explain why clarification was needed regarding the "intermediate timeframe is 2 to 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />." Describe whether the intermediate timeframe in the PRA model was changed to "2 to 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />" from some other values, and provide justification, as necessary, to support a change in timeframe.

b. Describe whether this change is comparable to example l-A.3.13 (Revised Modeling of Station Blackout) in the PRA Standard and if so, explain why this change is considered maintenance as opposed to an upgrade.

PRA RAI 2- Evaluation of the Change in Risk In Attachment 1 to the letter dated May 30, 2017 (ADAMS Accession No. ML17150A449), the licensee provided tables on pages 4 through 6 for delta (L'.l) core damage frequency (CDF) and i:l large early release frequency (LEAF).

i. Table - page 4, "Change in Risk from LaSalle County Station Pre-RI [risk informed]-ISI,Section XI Program to Fourth Interval RI-ISi Program," explain why both i:l CDF and i:l LEAF are roughly equivalent for each unit since LEAF is typically at least an order of magnitude lower than CDF.

ii. Table - page 5, "LaSalle County Station Unit 1 Delta-CDF and Delta-LEAF by System,"

explain why the values appear to have roughly equal i:l CDFs and i:l LERFs for the feedwater, main steam, reactor core isolation cooling and reactor water cleanup systems.

iii. Table - page 5, "LaSalle County Station Unit 1 Break Exclusion Region (BER) Weld Delta-CDF and Delta-LEAF by System," explain why the i:l CDF and i:l LEAF values for the emergency core cooling system (ECCS) are negative (implying a decrease)?

iv. Table - page 6, "LaSalle County Station Unit 2 Delta-CDF and Delta-LEAF by System,"

explain why the value for i:l LEAF for the ECCS system is negative.

v. Table - page 6, "LaSalle County Station Unit 2 Delta-CDF and Delta-LEAF by System,"

for both the ECCS and high pressure core spray systems (HPCS), explain why there is an increase (or decrease) for i:l CDF and the opposite trend for i:l LEAF.

vi. With respect to the ECCS:

a. Explain why the i:l CDF is positive as shown in the table on page 6, "LaSalle County Station Unit 2 Delta-CDF and Delta-LEAF by System," while the i:l CDF is negative as shown in the table on page 6, "LaSalle County Station Unit 2 BER Weld Delta-CDF and Delta-LEAF by System."

b. Explain why the i:l LEAF is greater in magnitude as shown in the table on page 6 "LaSalle County Station Unit 2 BER Weld Delta-GDF and Delta-LEAF by System" than the i:l LEAF shown in the table on page 6 "LaSalle County Station Unit 2 Delta-CDF and Delta-LEAF by System."

vii. With respect to the HPCS, explain why the i:l CDF is negative in the table on page 6, "LaSalle County Station Unit 2 Delta-CDF and Delta-LEAF by System," while the i:l CDF for the BER welds is positive as shown in the table on page 6, "LaSalle County Station Unit 2 BER Weld Delta-CDF and Delta-LEAF by System."

PRA RAI 3- Supporting Requirements (SRs) Not Met In the letter dated July 20, 2017 (ADAMS Accession No. ML172010396), both SR DA-C6 and DA-C10 state similar conclusions including:

"The plant data sources and developed demand estimates, however, are judged to be reasonable to support the PRA. Pursuing plant demand data per the explicit direction in the SR is not expected to result in significant impacts upon the PRA results. Therefore, DA-C6 is being self-assess as "Not Met" is not judged to impact this application."

Provide the justification for SRs that are not expected to result in significant impacts to the PRA.

Explain whether the data sources align with the four listed as acceptable in SR DA-C6.

PRA RAI 4- Safety Significance of Piping Segments Based on the information provided, the NRC staff could not determine whether the licensee reviewed the safety significance of the piping segments subject to inspection to ascertain whether there should be any changes in inspection locations for this fourth interval. Discuss whether there were any changes and, if so, explain the basis for those changes.

B. Hanson

SUBJECT:

LASALLE COUNTY STATION, UNITS 1 AND 2, REQUEST FOR ADDITIONAL INFORMATION REGARDING RELIEF REQUEST 14R-01, REQUESTS APPROVAL OF ALTERNATIVE RISK-INFORMED ISi PROGRAM AND EXAMINATION CRITERIA FOR EXAMINATION CATEGORY 8-F, 8-J, C-F-1, AND C-F-2 PRESSURE RETAINING PIPING WELDS IN ACCORDANCE WITH ASME CODE CASE N-578-1, "RISK-INFORMED REQUIREMENTS FOR CLASS 1, 2, OR 3 PIPING, METHOD B, SECTION XI, DIVISION 1."

(CAC NOS. MF9758 AND MF9759; EPID L-2017-LLR-0057) DATED OCTOBER 12, 2017 DISTRIBUTION:

PUBLIC RidsNrrPMLaSalle Resource RidsRgn3MailCenter Resource RidsAcrs_MailCTR Resource RidsNrrLASRohrer Resource RidsNrrDorlLp13 Resource RidsNrrDraApla Resource RidsNrrDeEpnb Resource ARezai, NRR/EPNB LFields, NRR/DRA/APLA RGallucci, NRR/DRA/APLA ADAMS Access1on No.: ML17261A078 (*)N o su bst an t"1a I c hanges f rom th eema1*1 OFFICE DORULPL3/PM DORL/LPL3/LA APLA/BC(*) DORULPL3/BC DORULPL3/PM NAME BVaidya SRohrer SRosenberg DWrona BVaidya DATE 9/25/2017 9/25/2017 9/21/2017 10/12/2017 10/12/2017 OFFICIAL RECORD COPY