TXX-9651, Forwards Assumptions & Results of Temporary Assessment of Limiting Peak Clad Temperatures

Forwards Assumptions & Results of Temporary Assessment of Limiting Peak Clad Temperatures

ML20135A684
Person / Time
Site:	Comanche Peak
Issue date:	11/29/1996
From:	Terry C TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TXX-96517, NUDOCS 9612040003
Download: ML20135A684 (16)

Text

e O Femme' Log # TXX-96517 MM File # 10010 h j 10CFR50.46

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- r filELECTRIC' November 29, 1996 C. Lance Terry Gnmp Mce President U. S. Nuclear Regulatory' Commission Attn: Document Control Desk Washington, DC 20555

SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)

DOCKET NOS. 50 445 AND 50 446 10CFR50.46 NOTIFICATION AND REPORTING INFORMATION REF: 1) Letter to C. L. Terry TU Electric, from Brian W. Sheron, Office of Nuclear Reactor Regulation, October 11, 1996

2) Letter logged TXX 96497, Dated October 25, 1996. from C. L. Terry to the NRC

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Gentlemen:

The large break loss of coolant accident (LOCA) analyses for Units 1 and 2 were performed by TU Electric in accordance with the approved TU Electric methodology. This methodology relied on the Siemens Power Corporation (SPC) 1986 evaluation model. On October 11, 1996, TU Electric was informed (Reference 1) by the NRC of an unacceptable error in the large break LOCA evaluation model used in the analysis of both CPSES Units 1 and

2. The error was characterized as non physical behavior of the reflood heat transfer coefficient for reflood rates between 1.0 and 1.77 inches /second. The NRC requested affected licensees to assess the impact of the model error and take whatever actions were required to assure compliance with 10CFR50.46.

In response to this request, TU Electric performed a temporary assessment, using guidelines agreed upon, at the October 16, 1996, meeting. The assumptions and results of this temporary assessment are documented in Reference 2.

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TXX 96517 l

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On November 20. 1996, after a preliminary review of Reference 2, the NRC l concluded that an assumption used in that tempor y assessment was no i

, longer acceptable. In that phone call the NRC .ommended a revised I

assessment using a code modification involvira a straight line j

- interpolation'on the reflood heat transfer coefficient for flooding rates '

in the range of concern. TU Electric then requested and the NRC agreed to a linear interpolation between 1.0-and 1.74. inches /second. The value of

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L 1.74 inches /second was justified by TV Electric and agreed upon by the NRC r

on the basis of a comparison between the correlation calculated value and  ;

experimental data points at 1.74 inches /second shown in Figure 3.7 of an ~j Attachment to Reference 2.  !

As a result of this conversation, the NRC requested TU Electric.to revise i its temporary assessment in the manner agreed upon in the November 20 l 1996 phone call between TU Electric and the NRC staff. The resulting PCTs and corresponding Fa values of that preliminary revised assessment using the interpolation end points of 1.0 and 1.74 inches /second were reported ,

to the NRC on the November _22, 1996, phone call. After some discussion, l TU Electric and the NRC mutually concluded that the end point of 1.74 inches /second, while theoretically appropriate, resulted in' excessive PCT reduction. The NRC then accepted the TU Electric proposal to use an intermediate point between 1.77 and 1.74 inches /second such that PCT reduction with respect to the base case of Reference 2 would be less than 50'F. 15e analysis initially concluded that the interpolation between 1.0 and 1.74 inches /second showed a reduction in PCT of approximately 195'F.

However, the final analysis resulted in a reduction in PCT of 42'F in Unit 1 and an increase in PCT of 24'F in Unit 2.

Thus, a new revised temporary assessment has been performed using a' code modification that does a straight line interpolation on the reflood heat ,

1 transfer coefficient for flooding rates between 1.0 and 1.74 inches /second. This new ravised temporary assessment demonstrates compliance with 10CFR50.46 and Appendix K thereto. pending the resolution of the issue with the heat transfer model in the Siemens 1986 evaluation model.

Based on this latest assessment, a list of the resulting licensing basis peak clad temperatures (PCT) for the LOCA analyses ls provided in  !

Attachment 1 to this letter. Additionally, Attachment 2 provides plant l specific information from the T00DEE2 hot rod heatup calculations i regarding the calculated peak clad temperature. TU Electric continues to satisfy the requirements of 10CFR50.46 and Appendix K thereto. The small break LOCA PCTs are bounded by the large break LOCA PCTs. j i

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TXX-96517 i Page 3 of 3 Please contact Dr. W. G. Choe at (214).812 4371 or Mr. J. D. Seawright at  :

(817) 897 0140 if you have any questions in this regard. I l

Sincere , ,

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C. L. Ter y  :

l JDS/grp l Attachments  !

c- Mr.'L. J. Callan, Region IV j Mr. T. J. Polich, NRR i Mr. J. I. Tapia, Region.IV l Resident Inspector. CPSES l

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Attachment 1 to TXX 96517 -l Page 1 of 1 J

CPSES Units 1 and 2 Limiting Peak Clad Temperatures  :

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CPSES Unit 1 CPSES Unit 2 i 2 l

. Total Total Peakina Peakino Analysis / Evaluation PCT (*F) Factor (Fe ) PCT ("F) Factor (Fe)

Limiting LOCA PCT (*F) 2055 2.42 2048 2.42

[Large Break)

Revised Temporary 2013 2.42 2072 2.42 l Assessment pending i resolution of SPC I issues with 1986 )

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