ML12115A004

Email to Convey RAI Thermal Conductivity Degradation

ML12115A004
Person / Time
Site:	Cook
Issue date:	04/23/2012
From:	Tam P Plant Licensing Branch III
To:	Etheridge H Indiana Michigan Power Co
Tam P
References
TAC ME8322, TAC ME8323
Download: ML12115A004 (3)

Text

Accession No. ML12115A004 From: Tam, Peter Sent: Monday, April 23, 2012 11:02 PM To: hletheridge@aep.com; 'jrwaters@aep.com'; mkscarpello@aep.com Cc: Parks, Benjamin; Paige, Jason; Lennartz, Jay; LaFlamme, Paul; Giessner, John

Subject:

D.C. Cook - Request for Additional Information Regarding Thermal Conductivity Degradation (TAC ME8322 and ME8323)

Helen:

By letter dated March 19, 2012 (Accession No. ML12041A384), Indiana Michigan Power Company submitted a response to an NRC staffs 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).

In the course of its 10 CFR 50.46 report review, the NRC staff determined that additional information is necessary to complete its review. A draft copy of this request for additional information was provided to facilitate discussion with the licensee; subsequently, the NRC staff conducted an audit at the Westinghouse Electric Company facilities in Cranberry Township, Pennsylvania, to further clarify the request for additional information and the content required to be responsive to the request (Accession No. ML12094A069). The draft request for additional information has been revised (see below) to provide additional clarity.

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) RCS Tavg, (9) Accumulator Temperature, (10) Safety Injection Temperature, (11) Safety Injection Time.

2. Please 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 WCOBRA/TRAC cases that were re-executed, as opposed to a larger number of cases.

3. Justify the containment pressure changes made to obtain margin on Unit 1.

Provide reference to excerpts from the applicable methodologies to clarify the response.

4. Justify the evaluation of reduced peaking factors at beginning-of-life conditions to obtain analytic margin to offset the TCD effect. Show that peaking factor reductions affect PCT in a manner that is substantially independent of fuel burnup.

5. 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 D.C. Cook, including the relevant conclusions and the technical basis supporting those conclusions. For any conclusion that differences in void volume 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.

b. Please provide the values for the coefficients A1 and A2 used in the PAD 4.0 +

TCD UO2 thermal conductivity equation.

c. Please explain any error corrections, code improvements, and miscellaneous code cleanup between the WCOBRA/TRAC and HOTSPOT code versions used in the TCD evaluations and those used in the plants 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. Please provide additional detail concerning the steady-state ASTRUM/CQD initialization process. In particular, please explain what fuel characteristics are adjusted within the applicable models to obtain convergence among HOTSPOT, WCOBRA-TRAC, and PAD4.0TCD.

6. Please explain how the changed design values will be verified during operation of the plant, i.e. TS 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.

7. Fully explain all peaking factor adjustments and provide the rationale for each adjustment.

8. At the bottom of Page 1 of Enclosure 2 to AEP-NRC-2012-13 it is stated that I&M and WEC utilized processes which ensure that the LBLOCA analysis input values conservatively bound the as-operated plant values for those parameters.

Please explain these processes.

9. Please explain the process for determining the establishment of a trend in the context of the following statement: For the margin PCT calculation, WCOBRA/TRAC cases were executed until an estimated trend could be established.

10. Based on the NRCs review of the xxxx, 2012, submittal it appears that the licensee has revised inputs to a method of evaluation as described in the FSAR (as updated) used in establishing the design bases or in the safety analyses.

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. Further, address whether any of the changes (i.e., to the UO2 thermal conductivity equation) constitute a change in the calculational framework used for evaluating behavior or response of a system, structure or component We request that you provide your formal response on or before May 25, 2012.

If you need to discuss any of the above questions with the NRC staff, or the requested response date, or need to have the above questions issued by a letter, please do not hesitate to call me.

Peter S. Tam, Senior Project Manager (for D.C. Cook and Monticello)

Plant Licensing Branch III-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Tel. 301-415-1451