ML14255A088

Response to Draft Request for Additional Information - License Amendment Request - Main Steam Line Flow-High Isolation Response Time Change from ≪ 0.5 Seconds to ≪ 1.0 Seconds

ML14255A088
Person / Time
Site:	Limerick
Issue date:	09/11/2014
From:	Jim Barstow Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML14255A088 (5)

Text

10 CFR 50.90 September 11, 2014 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Units 1 and 2 Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353

Subject:

Response to Draft Request for Additional Information - License Amendment Request - Main Stearn Line Flow-High Isolation Response Time Change from s 0.5 seconds to s 1.0 seconds

References:

1) Letter from J. Barstow (Exelon Generation Company, LLC) to U.S.

Nuclear Regulatory Commission, "License Amendment Request - Main Stearn Line Flow-High Isolation Response Time Change from s 0.5 seconds to s 1.0 seconds, 11 dated November 15, 2013

2) Internal Memorandum from R. B. Ennis (Senior Project Manager, U.S.

Nuclear Regulatory Commission) to M. K. Khanna, Chief, Plant Licensing Branch 1-2, U.S. Nuclear Regulatory Commission), 11 Lirnerick Generating Station, Units 1 and 2, Draft Request for Additional Information (TAC Nos. MF3085 and MF3086)," dated March 7, 2014, (ML14066A097)

3) Letter from J. Barstow (Exelon Generation Company, LLC) to U.S.

Nuclear Regulatory Commission, 11 Response to Request for Additional Information - License Amendment Request - Main Stearn Line Flow-High Isolation Response Time Change from s 0.5 seconds to s 1.0 seconds, 11 dated April 16, 2014

4) Internal Memorandum from R. B. Ennis (Senior Project Manager, U.S.

Nuclear Regulatory Commission) to R.G. Schaaf, Acting Chief, Plant Licensing Branch 1-2, U.S. Nuclear Regulatory Commission), "Limerick Generating Station, Units 1 and 2, Draft Request for Additional Information (TAC Nos. MF3085 and MF3086)," dated July 21, 2014 (ML14202A518)

U.S. Nuclear Regulatory Commission Response to Request for Additional Information -

LAR - Main Steam Line Flow-High Isolation Response Time September 11, 2014 Page2 In the Reference 1 letter, Exelon Generation Company, LLC (Exelon) requested changes that would modify Technical Specification (TS) Table 3.3.2-3, "Isolation System Instrumentation Response Time, 11 for the Main Steam Line Flow-High from s 0.5 seconds to s1 .o seconds. In the Reference 2 memorandum, the U.S. Nuclear Regulatory Commission requested additional information regarding instrument channel response. Exelon responded in Reference 3. In the Reference 4 memorandum, the U.S. Nuclear Regulatory Commission requested additional information regarding accident analysis. Attachment 1 contains our response.

Exelon has reviewed the information supporting a finding of no significant hazards consideration and the environmental consideration provided to the U.S. Nuclear Regulatory Commission in Reference 1. The additional information provided in this response does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. Furthermore, the additional information provided 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 commitments contained in this response.

Should you have any questions concerning this letter, please contact Frank Mascitelli at (610) 765-5512.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 11th day of September 2014.

Respectfully, James Barstow Director, Licensing & Regulatory Affairs Exelon Generation Company, LLC Attachments: 1) Response to Draft Request for Additional Information cc: USNRC Region I, Regional Administrator USNRC Senior Resident Inspector, LGS USNRC Senior Project Manager, LGS Director, Bureau of Radiation Protection - PA Department of Environmental Resources

ATTACHMENT 1 License Amendment Request Limerick Generating Station, Units 1 and 2 Docket Nos. 50-352 and 50-353 Response to Draft Request for Additional Information License Amendment Request Regarding Main Steam Line Flow-High Isolation Response Time

Attachment 1 Page 1 Response to Draft Request for Additional Information License Amendment Request Regarding Main Steam Line Flow-High Isolation Response Time In the Reference 1 letter, Exelon Generation Company, LLC (Exelon) requested changes that would modify the Limerick Generating Station (LGS) Technical Specification (TS) Table 3.3.2-3, "Isolation System Instrumentation Response Time," for the Main Steam Line Flow-High from s 0.5 seconds to s 1.0 seconds. The NRC reviewed the license amendment request and identified the need for additional information in order to complete their evaluation of the amendment request. A draft request for additional information (RAI) was electronically transmitted to Exelon on July 21, 2014 (Reference 4). The questions are restated below along with Exelon's response.

RAI Question 1 Section 3.0 of Attachment 1 to the application dated November 15, 2013, states that the current analysis of record for the LGS main steam line break (MSLB) loss-of-coolant accident peak cladding temperature response is documented in General Electric topical report NEDC-32170P, Revision 2, dated May 1995. If this topical report has already been submitted to the NRC, please identify the document which submitted the report, otherwise submit the report.

Response

General Electric report NEDC-32170P, Revision 2, dated May 1995, is the SAFER/GESTR LOCA application report for LGS and documents the MSLB loss-of-coolant accident (LOCA) peak cladding temperature result. Access to this report has been provided to the NRC staff via the Limerick eDocs database. In addition, a request to GE Hitachi Nuclear Energy has been made to provide a non-proprietary version and affidavit for NEDC-32170P, Revision 2, which will be submitted when received by Exelon.

RAI Question 2 Section 4.1 of Attachment 1 to the application lists 10 CFR Part 50, Appendix A, General Design Criterion (GDC) 46 as "Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors." That title pertains to 10 CFR 50.46, not GDC 46. Please clarify the applicable regulatory requirements/criteria that pertain to this amendment request.

Response

The reference to 10 CFR 50, Appendix A, GDC 46 is an administrative error. The applicable regulatory requirement/criterion is 10 CFR 50.46, "Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors."

Response to Draft Request for Additional Information License Amendment Request Regarding Attachment 1 Main Steam Line Flow-High Isolation Response Time Page 2 RAI Question 3 As discussed in Section 3.0 of Attachment 1 to the application, GE Hitachi Nuclear Energy (GEH) performed a MSLB outside of containment (STMO) analysis using the evaluation model SAFER04A. The licensee stated that the SAFER simulation of the analysis provides fuel heat-up and long-term cooling system response. The NRC staff requests that the licensee provide additional information to support the following statement in the submittal: "This methodology is more accurate than the current method which is based on simplifying assumptions as described in UFSAR [Updated Final Safety Analysis Report] Section 15.6.4." In addition, Attachment 4 to the application, GEH document 0000-0158-9651-NP, states on page 3 that:

LGS UFSAR 15.6.4.4.f: "Level rise time is conservatively assumed to be 1 second. Mixture quality is conservatively taken to be a constant 7% (steam weight percentage) during mixture flow." This assumption is not necessary.

SAFER is a systems code and can calculate the time varying two phase break flow during the STMO event.

The original and the newly submitted analysis are based on SAFER evaluation model. Why is the above assumption not necessary now? Describe the SAFER code changes, if any, to justify the deletion of this key assumption.

Confirm whether or not the following assumptions currently listed in UFSAR Section 15.6.4.4, and discussed in Attachment 1 to the application, will be revised as part of the implementation of the proposed amendment:

d. Isolation valves start to close at 0.5 seconds on high flow signal and are fully closed at 5.5 seconds.

f. Level rise time is conservatively assumed to be 1 second. Mixture quality is conservatively taken to be a constant 7% (steam weight percentage) during mixture flow.

Response

The current method for determining the LGS MSLB mass flow for dose analysis is based on conservative simplifying assumptions as described in LGS UFSAR Section 15.6.4 and is not based on the SAFER evaluation model. The proposed method for dose analysis is based on analyses performed utilizing the SAFER 04A code/model for LGS. SAFER is a systems code that calculates the time varying reactor level response and two phase mass flow during the MSLB event. Therefore, the current simplifying assumptions in the LGS UFSAR do not apply to the proposed method. No changes to the SAFER code were required to perform the analyses.

As part of the implementation of the proposed amendment, LGS UFSAR Section 15.6.4.4, including the currently listed assumptions, will be revised accordingly to reflect the basis of the proposed method as described in the license amendment request.