ML20209E042

Forwards Response to NRC Request for Addl Info on LAR 98-010.Attachment 1 Is Affidavit for Info Supporting LAR 98-010

ML20209E042
Person / Time
Site:	Comanche Peak
Issue date:	07/09/1999
From:	Terry C, Walker R TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TXX-99164, NUDOCS 9907140131
Download: ML20209E042 (7)

Text

. .

i I]

=

Log # TXX-99164 File # 916 (3/4.3) ,

10010 1 7UELECTRIC Ref. # 40CFR50.90 10CFR50.36 c.u ce nrry senior vice Presiden July 9,1999

& PrincipalNuclear Officer 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 RESPONSE TC NRC REQUEST FOR ADDITIONAL INFORMATION ON LICENSE AMENDMENT REQUEST 98-010 (TAC Nos. MA4436 and MA4437)

REF: TXU Electric' letter, logged TXX-98265, from C. L. Terry to the NRC dated December 21,1998 Per Reference 1, TXU Electric submitted a request to amend the CPSES Unit 1 Operating License (NPF-87) and CPSES Unit 2 Operating License (NPF-89) by incorporating changes into the CPSES Units 1 and 2 Technical Specifications and the CPSES Unit 2 Operating License to increase the licensed power for operation of CPSES Unit 2 to 3445 Mwt; an increase of approximately 1%.

Per telephone conversation with NRR on July 7,1999, TXU Electric received a request to provide the attached additionalinformation regarding License Amendment Request 98-010.

Attachment 1 is the affidavit for this information supporting License Amendment Request 98-010. Attachment 2 provides our response to the inforration requested.

\

l nM 9907140131 990709 9 PDR ADOCK 05000445 P PDR 8

TXU Electric was formerly TU Electric. A license amendment request (LAR 99-003) was submitted per TXX-99122, dated May 14,1999, to revise the company name contained in the CPSES operating licenses.

COMANCHE PEAK SibAM ELECTRIC STATION Qp]Q P.O. Box 1002 Glen Rose. Texas 76043-1002

TXX-99164 Page 2 of 2 In accordance with 10CFR50.91(b), TXU Electric is providing the State of Texas with a copy of this supplement to the proposed amendment.

Should you have any questions, please contact Mr. Obaid Bhatty at (254) 897-5839. This communication contains no new licensing basis commitments regarding CPSES Units 1 and 2.

Sincerel

e. 0 C. L. Terry By: M '

Roger [YWalker Regulatory Affairs Manager OAB/oab

Attachment:

1. Affidavit

2. Responses to NRC Questions cc: Mr. E. W. Merschoff, Region IV Mr. D. H. Jaffe, NRR Mr. J.1. Tapia, Region IV Resident inspectors, CPSES Mr. Arthur C. Tate Bureau of Radiation Control Texas Department of Public Health 1100 West 49th Street Austin, Texas 78704 ,

i l

l

Attachment 1 to TXX-99164 )

Page 1 of 1 l

i l

UNITED STATES OF AMERICA l

NUCLEAR REGULATORY COMMISSION

\

in the Matter of )

) 1 Texas Utilities Electric Company ) Docket Nos. 50-445

) 50446 (Comanche Peak Steam Electric ) License Nos. NPF-87 Station, Units 1 & 2) ) NPF-89 AFFIDAVIT Roger D. Walker being duly sworn, hereby deposes and says that he is the Regulatory Affairs Manager of TXU Electric, the licensee herein; that he is duly authorized to sign and file with the Nuclear Regulatory Commission this supplement to License Amendment Request 98-010; that he is familiar with the content thereof; and that the matters set forth therein are true and correct '

to the best of his knowledge, information and belief. ,

@ h' Roger DVNalker Regulatory Affairs Manager STATE OF TEXAS )

)

COUNTY OF SOMERVELL )

Subscribed and sworn to before me, on this day of I 4 .1999.

jQ, f gygj G2y'a R. Peck Jespersen ,

Notary /Public /

. MWfs#feita 3

%v

Rcsponses to NRC Questions Attachment 2 to TXX-99164 l

o Attachment 2 to TXX-99164 Page 1 of 3 Responses to NRC Questions 1

i

1. The Ilcensee needs to evaluate the effects of the power uprate on the tube \

degradation mechanisms (present and potential) including wear.

TXU Electric Resoonse to Reauest 1:

TXU Electric has evaluated the effects of the power uprate on tube degradation mechanisms including tube wear, and concluded that the uprate will have negligible impact on the existing and potential tube degradation mechanisms. However, during the telephone conference, your staff requested that TXU Electric provide additional information on corrosion, anti vibration bar (AVB) and preheater tube wear. This information is provided below:

CORROSION The proposed 1 percent uprating of Comanche Peak Steam Electric Station (CPSES)

Unit 2 will result in an approximate 0.3*F increase in the primary inlet temperature to the I' steam generators, T , which is considered to be the most sensitive operating parameter with respect to corrosion. The primary system nominal operating pressure of 2250 psia will remain unchanged for the CPSES Unit 2 uprate condition. Steam pressure, which is considered to have a secondary effect on corrosion, will decrease approximately 4 psi. With the current 0.1 percent steam generator tube plugging, this will change the secondary normal operating steam pressure from 1000 psia to 996 psia.

CPSES Unit 2 has operated for 5 effective full power years (EFPY) without any l corrosion-related degradation of steam generator tubing. The steam generator tube  !

material is thermally treated alloy 600, which is known to have improved corrosion resistance over mill annealed alloy 600. The steam generator geometry and manufacturing processes incorporate other factors (hydraulically expanded tube-to-tubesheet joints, stainless tube steel support plates with quatrefoil cutouts, etc.) which also improve corrosion characteristics in these steam generators. In other plants, Byron Unit 2 for example, steam generators with the same tube material have operated successfully for 13 EFPY under conditions similar to the CPSES uprating with no active corrosion of the steam generator tubing. Other parameters which have minor affects on corrosion such as steam temperatures and flows have also been evaluated for the CPSES uprated conditions and have been found to have a negligible impact on steam generator tube corrosion. Based on these experiences, CPSES steam generators in Unit 2 are not expected to experience any significant increase in corrosion.

AVB WEAR AVB wear or any tube (or other component) wear issues caused by flow induced vibration or other mechanism can be evaluated using two methods. First, a pre-uprating evaluation, using both theoretical considerations and the actual tube wear conditions;

Attachment 2 to TXX-99164 Page 2 of 3

' and secondly, a post uprating evaluation using wear projection technology (WPT)2 The WPT evaluation produces the information required to monitor tube wear during operation under the uprated condition.

A pre-uprating evaluation was also performed using thermal-hydraulic parameters for the uprated condition. It was concluded that the wear rates prior to the uprating and the projected wear rates after the uprating remain negligible.

PREHEATER WEAR A preliminary assessment has been performed to estimate the effects of a proposed 4.5 percent power uprate at CPSES Unit 2 with respect to preheater tube wear. A review of eddy current inspection results for preheater tubes was also performed in support of this effort. No tubes were plugged as a result of wear in the preheater, and only two tubes in this region had any indications of wear. The maximum wear depth of the limiting tube was estimated to be approximately 5 percent through wall. From this review, it has been concluded that significant preheater tube wear is not active in the CPSES Unit 2 steam generators. As a result of the proposed uprate, the total feedwater flow into the steam generator will increase. With increased flow through the main feedwater nozzle, the potential for tube wear could also increase. Calculations have been performed to estimate the level of increased tube wear that could occur for the limiting uprate condition. From this review, it has been determined that the rate of wear could increase by a factor of approximately 1.6.

Eddy current inspection results indicate that the current rate of preheater tube wear is not significant and is either not occurring or is occurring at a very low rate. Therefore, an increase in the current wear rate by a factor of 1.6 is not projected to result in a

- significant wear rate (1.6 multiplied by a very small number remains a small number). In addition, it should be noted that the evaluation and tests performed to support the

. current flow conditions at CPSES Unit 2 were performed using a flow rate that is actually larger than the flow rate expected when operating at the uprated power.

TXU Electric will continue to monitor the tubes located in the preheater in accordance with the Steam Generator Integrity Program required by the Technical Specifications to

- determine if significant tube wear is occurring. Should tube wear be identified, appropriate actions (such as wear projection, tube plugging / stabilization, or orifice plate modifications) will be considered.

2 ASME Paper "An Empirical Wear Projection Technology with Steam Generator Tube Applications and Relations to Work-Rate and Wear Simulations / Tests," T. M. Frick, AD-Vol. 53-2, Fluid-Structure Interaction, Aeroelasticity, Flow-induced Vibration and Noise, Volume 11, Dallas, Nove.1ber 1997.

F Attachment 2 to TXX-99164 Page 3 of 3

2. Discuss how steam generator tube inspection plan will be assessed to monitor potential tube degradation including wear. Will additionalinspections be necessary? How will TXU Electric assess their inspection plans should new k degradation mechanisms be discovered?

l TXU Electric Resoonse to Reouest 2:  !

As stated in response to request 1, TXU believes that the uprating will not introduce new degradation mechanisms. Hence, adequate confidence exists that the current steam generator integrity program (which encompasses WPT) is acceptable. Nonetheless, the need for additional surveillances or inspection criteria will be developed as necessary, as described in TXU Electric's current steam generator integrity program. It is TXU Electric's position that the uprating changes introduced by the small 1 percent uprate (approximately 0.3"F increase in Tw) are not sufficient to require pre-emptive changes to the existing program.

l

3. The licensee needs to evaluate if the Technical Specification plugging limit of 40 percent through wall degradation is still adequate.

TXU Electric Resoonse to Reauest 3 :

A structural evaluation was performed to determine whether the tube plugging limit of 40 I percent through wall used by the Steam Generator Integrity Program, implemented as required by the Technical Specifications, would remain applicable when operating at the uprated power conditions. These calculations address the conditions that were historically found to be limiting in analyses performed for similar plants. Based on these analyses, the loading conditions used in the current analysis were judged to remain valid.

The loading conditions considered to be most limiting for through-wall degradation is associated with the primary to-secondary pressure differential. Conditions associated with a 4.5 percent power uprating were evaluated for normal operations, normal and upset transients, and faulted conditions.

Considerations were also given to the burst-pressure and the collapse limits of tube.

Comanche Peak Unit 2 does not have any active corrosion mechanism contributing to tube degradation. Nonetheless, the structural limit permits a 22.8 percent allowance for NDE growth and eddy current measurement uncertainty that is adequate to bound prior experience at Comanche Peak Unit 2 for degradation applying the 40 percent plugging limit.

On the basis of this evaluation, it is concluded that the technical justification for the current 40 percent technical specification tube plugging limit remains valid and would not be impacted by even a bounding 4.5 percent power uprating.