ML12128A136

Request for Additional Information Related to 10 CFR Part 50.46 30-Day Report

ML12128A136
Person / Time
Site:	Byron, Braidwood
Issue date:	05/10/2012
From:	Joel Wiebe Plant Licensing Branch III
To:	Pacilio M Exelon Nuclear
Wiebe J
References
TAC ME8470, TAC ME8471
Download: ML12128A136 (5)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 May 10, 2012 Mr. Michael J. Pacilio President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, I L 60555

SUBJECT:

BYRON STATION, UNIT NO.2, AND BRAIDWOOD STATION, UNIT 2 REQUEST FOR ADDITIONAL INFORMATION RELATED TO 10 CFR PART 50.46 30-DAY REPORT (TAC NOS. ME8470 AND ME8471)

Dear Mr. Pacilio:

By letter dated March 19, 2012 (Agencywide Document Access and Management System (ADAMS) Accession No. ML12079A112), Exelon Generation Company, LLC (the licensee),

submitted a response to a U.S. Nuclear Regulatory Commission (NRC) information request pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.54(f) related to the estimated effect on peak cladding temperature resulting from thermal conductivity degradation in the Westinghouse furnished realistic emergency core cooling system evaluation. The licensee also stated that this response served as a 30-day report of a Significant emergency core cooling system evaluation model change or error in accordance with requirements of 10 CFR 50.46(a)(3).

The NRC staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested was provided to you via e-mail on May 3, 2012, and is also addressed in the enclosure to this letter. During a discussion with your staff on May 7,2012, it was agreed that you would provide a response within 30 days from the date of this letter.

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

M. Pacilio

- 2 If circumstances result in the need to revise the requested response date, please contact me at (301) 415-6606.

Sincerely, oel S. Wiebe, Senior Project Manager Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-457 and STN 50-455

Enclosure:

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

REQUEST FOR ADDITIONAL INFORMATION BYRON STATION, UNIT NO.2, AND BRAIDWOOD STATION, UNIT 2 DOCKET NOS. STN 50-455, AND STN 50-457 By letter dated March 19, 2012 (Agencywide Document Access and Management System (ADAMS) Accession No. ML12079A112), Exelon Generation Company, LLC (the licensee),

submitted a response to a U.S. Nuclear Regulatory Commission (NRC) information request pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.54(f) related to the estimated effect on peak cladding temperature resulting from thermal conductivity degradation in the Westinghouse furnished realistic emergency core cooling evaluation. The licensee also stated that this response served as a 30-day report of a significant emergency core cooling system evaluation model change or error in accordance with requirements of 10 CFR 50.46(a)(3).

During the review of the 10 CFR 50.46 report review, the staff determined that the following additional information is necessary to complete its review:

1. Provide a table of data that includes the following ASTRUM inputs for AOR and integrated analyses: (1) AOR Run #, (2) TCD Run #, (3) PCT, (4) Time of PCT, (5) Fq, (6) FdH, (7) Cycle Burnup, (8) Margin Only PCT, (9) TCD Minus Margin Only Delta.

2. Highlight the limiting cases in the ASTRUM run matrices and explain how these cases were chosen. Provide details and explain the approach used to estimate (1) the effects of TCD and (2) the compensating model changes. Justify the selection of the number of WCOBRAITRAC cases that were re-executed, as opposed to a larger number of cases.

3. Justify the containment pressure changes made to obtain margin. Provide reference to excerpts from the applicable methodologies to clarify the response.

4. Your submittal referenced a March 7, 2012, letter sent by Westinghouse Electric Company to the NRC.

a. The final paragraph on Page 2 of 9 refers to small differences in fuel characteristics that were claimed to be compared. The paragraph also discusses confirmatory evaluations concluding that other operating characteristics were acceptable. Provide the results of this comparison for Braidwood Unit 2 and Byron Unit No.2, including the relevant conclusions and the technical basis supporting those conclusions. For any conclusion that differences in a particular fuel or operating characteristic are offset by other conservatisms, list those conservatisms and provide a quantitative estimate of each conservatism, as well as a brief description of the rigor associated with that estimate.

Enclosure

- 2

b. Provide the values for the coefficients used in the PAD 4.0 + TCD U02 thermal conductivity equation.

c.

Explain any error corrections, code improvements, and miscellaneous code cleanup between the WCOBRAfTRAC and HOTSPOT code versions used in the TCD evaluations and those used in the plant's AOR.

d. What is the thermal conductivity model impact of code version changes in HOTSPOT?

e. Explain the differences between the HOTSPOT and PAD thermal conductivity models and the impact of those differences. Provide graphs or other quantified descriptions that aid in explanation.

f.

Provide additional detail concerning the steady-state ASTRUM/CQD initialization process. In particular, explain what fuel characteristics are adjusted within the applicable models to obtain convergence among HOTSPOT, WCOBRA-TRAC, and PAD4.0 + TCD.

5. Explain how the changed design values will be verified during operation of the plant, i.e.,

technical specification limits, surveillances, etc. Also, explain what compensatory actions will be taken if a value is found to be outside of the limits assumed in the analysis.

6. At the top of Page 2 of Attachment 1 to your March 19, 2012, submittal, it is stated that, "EGC and its vendor, Westinghouse Electric Company, LLC, utilized processes which ensure that the LOCA analysis input values conservatively bound the as-operated plant values for those parameters." Explain these processes,

7. Based on the review of your March 19, 2012, submittal it appears that you revised the inputs to a method of evaluation as described in the FSAR (as updated) used in establishing the design bases or in the safety analyses.

Revision 1 to NEI 96-07, "Guidelines for 10 CFR 50.59 Implementation," Section 3.B, "Input Parameters," provides clarifying information concerning whether an input parameter is considered to be an element of a methodology for the purposes of addressing the applicable requirements found at 10 CFR 50.59, "Changes, Tests, and Experiments." Address whether the methodology permits the licensee to establish how to select the value of an input parameter to yield adequately conservative results and whether the revised value is more conservative than that required by the selection method.

Address whether any of the changes (i.e., to the U02 thermal conductivity equation) constitutes a change in the calculational framework used for evaluating behavior or response of a system, structure or component. Explain whether and how 10 CFR 50.59(c)(4) might apply to such a change.

M. Pacilio

-2 If circumstances result in the need to revise the requested response date, please contact me at (301) 415-6606.

Docket Nos. STN 50-457 and STN 50-455

Enclosure:

Request for Additional Information cc w/encl: Distribution via Listserv DISTRIBUTION:

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